Evaluation of a Computer-directed Pneumatic-tube System for Pneumatic Transport of Blood Specimens DON K. WEAVER, M.D., DORLAND MILLER, C(ASCP), EDWIN A. LEVENTHAL, PH.D., AND VINCENT TROPEANO
M O D E R N , W E L L - E Q U I P P E D hospitals use pneumatic-tube systems to speed the flow of requisitions, results, messages, and small supply items. The potential uses of these fast delivery systems for sending body-fluid specimens for analysis have produced interest and controversy. 2 - 5 Before sending specimens through a pneumatic tube, two criteria must be fulfilled: the results of analysis of blood specimens must be unaffected by their journey, and the journey must be safe for the specimen to preclude contamination of the system by breakage. Two previous studies demonstrated that serum or plasma sodium, chloride, carbon dioxide, inorganic phosphorus, calcium, urea, uric acid, glucose, alanine aminotransferase, aspartate aminotransferase, creatinine, total protein, fibrinogen, hemoglobin, and bilirubin could be safely transported through existing pneumatic tubes but that values for lactate dehydrogenase (LDH), potassium, acid phosphatase and serum hemoglobin were artifactually elevated. A recent abReceived April 6, 1977; received revised manuscript May 23, 1977; accepted for publication May 23, 1977. Address reprint requests to Dr. Weaver: Williamsport Hospital, 777 Rural Ave., Williamsport, Pennsylvania 17701.
Williamsport Hospital and Friesen International, Inc., Williamsport, Pennsylvania
stracted account reported statistically significant differences in LDH, aspartate aminotransferase, and glucose. 2 - 5 On the other hand, using a pilot system, another evaluation of a pneumatic-tube system reported no difference in values of acid phosphatase, potassium, aspartate aminotransferase, glucose, or lactic dehydrogenase in specimens delivered by pneumatic and manual methods. 4 Others' experience with pneumatic transportation of specimens reveals that each system should be assessed for the effect of pneumatic transportation upon chemical constituents measured. We propose to report upon our results from the transportation of blood specimens through a pneumatic-tube system. The tests were conducted under routine working conditions in a hospital laboratory. Materials and Methods The pneumatic-tube system used at the Williamsport Hospital is a Trans-Logic 200.* Carriers are directed through 4" diameter (10-cm) steel conduits to various stations throughout the hospital at speeds of as much as 25 feet/sec (7.6 meters/sec). The blowers and transfer units are controlled and monitored by a central processor that has stored the required transaction data. The computer directs carriers to their destination via the shortest, most direct route available. The carriers are constructed of a translucent plastic with a 15-inch (37.5-cm) inside length and have a nominal load capacity of 2.75 lb (1.25 kg). Molded foam-rubber inserts prevent movement of collection tubes within the carrier (Fig. 1). The carrier can be inserted into the system in either direction but cannot be inserted unless the two sections are securely latched. Samples transported by the system for this study originated either at the outpatient department or at one of the inpatient areas. The outpatient samples were dispatched from the laboratory pneumatic station and * Powers Regulator Corp. Colorado.
Transitube Division, Denver,
0002-9173/78/0900/0400 $00.75 © American Society of Clinical Pathologists
400
Downloaded from http://ajcp.oxfordjournals.org/ by guest on March 19, 2016
Weaver, Don K., Miller, Dorland, Leventhal, Edwin A., and Tropeano, Vincent. Evaluation of a computer directed pneumatic tube system for pneumatic transport of blood specimens. Am J Clin Pathol 70: 400-405, 1978. The results of sending specimens through a computerized pneumatic airtransport system and manually delivering specimens were compared for 15 chemical tests and six hematologic procedures. All specimens were collected from inpatients and outpatients into evacuated glass containers. The specimens traversed a maximum of 829 feet (253 meters) involving 16 bends and eight transfer units at 25 feet/second (7.6 meters/second). Only the activity of lactate dehydrogenase exceeded the precision of the test in pneumatically transported specimens. Ruptured erythrocytes in incompletely filled vacuum tubes were the likely source of the increased lactate dehydrogenase activity. Neither the serum sodium, potassium, chloride, carbon dioxide, total protein, albumin, calcium, glucose, creatinine, total bilirubin, alkaline phosphatase, aspartate transaminase, acid phosphatase, uric acid, leukocyte count, erythrocyte count, hemoglobin, hematocrit, nor the prothrombin time and partial thromboplastin time were affected by pneumatic transport. It is concluded that the pneumatic system tested provides a safe, efficient method of transporting the blood specimens tested. (Key words: Pneumatic transport; Blood specimens.)
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FIG. I. Opened plastic transport container lined with foamrubber inserts.
Sample and Test Methods All blood was obtained from patients at the Williamsport Hospital, a 370-bed general hospital in Williamsport, Pennsylvania. Duplicate blood samples were drawn from inpatients during routine morning and afternoon collections and from outpatients whenever they arrived at the laboratory. Stat tests and requests from patients in the nursery and critical care units were excluded from the study. Each blood sample was labeled with the patient's name, hospital number, date drawn, and time drawn. The venipuncturist coded the two blood specimens with a prestuck label A, B, or C; the remaining label was applied to the request slip. The venipuncturist randomly sent one labeled specimen (A, B, or C) through the pneumatic tube and handcarried the other specimen to the laboratory. Specimens from hospitalized patients came from any of five floors; therefore, the distances traveled by the specimens in the pneumatic tube varied. Specimens drawn from outpatients traveled from the laboratory to the most distant receiving station and back to the laboratory, traversing roughly twice the distance traversed by specimens sent from inpatient wards. A test coordinator, unassociated with the clinical laboratory, received the samples, recorded the pertinent data, coded the specimens, and distributed all manually and pneumatically transmitted samples promptly to the laboratory personnel, who were unaware of the source of the samples. Blood samples sent to Chemistry were centrifuged, and 15 serum chemical constituents were determined (Table 1). Blood received in Hematology was mixed, and the Coulter S was used to determine the leukocyte count, erythrocyte count, hemoglobin, and hematocrit.
Prothrombin and partial thromboplastin times were measured in an ML A Electra 500 (Table 1). Test results were returned to the test coordinator, who verified the correctness of the identifying information (patient name, test number, and appropriate code letter). The test results were matched to original work papers to indicate which specimen was test and which was control. A change in the source of reagents for lactate dehydrogenase and aspartate transaminase necessitated a second study of these enzymes five months after the initial test. The design of the test was identical to that of the previous study except that the Beckman TR replaced the SMA 12/60 to determine aspartate transaminase (Table 1). The effect of movement of blood in the evacuated container was tested by drawing blood from each of 20 outpatients into two 10-ml Monojet evacuated glass tubes. One tube wasfilledto its capacity; the other tube was filled to half its capacity. Before the blood clotted, both containers were sent through the pneumatic tube from the laboratory office to the end of the system and returned. Following prompt centrifugation and separation of the serum from the clot, lactate dehydrogenase activity of both samples was determined. The standard deviation for each test was obtained from results of lyophilized pooled serum controls. Methods of Data Analysis Because the data were collected from paired samples (one of each pair delivered manually and one delivered pneumatically), the t ratio was chosen as the quantity for determining statistical significance. The t ratio represents the mean difference of all pairs in the sample group divided by the standard error of the differences in the sample group. In Student's t distribution a t ratio greater than 2 represents 95% confidence that the mean difference is not zero. Sample groups of the type studied here do not usually fit Student's t distribution precisely; however, the differences are not considered
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traveled through 829.84 feet (253 meters) of straight tube, 16 bends, and eight transfer units before returning to the laboratory. Samples from inpatient areas traveled a distance approximately 50% of that traversed by the outpatient specimens.
402
WEAVER ET AL.
significant for the purposes being investigated. After establishing which of the test results had a non-zero difference, with 95% confidence, the differences were compared with the standard deviation for the respective test methods and the equipment used. Differences of less than one standard deviation were judged not significant for clinical diagnostic purposes. Results
confidence level. In all cases but the two LDH tests, the differences were less than one standard deviation ofthe test method and were within the precision limits ofthe test. Figure 2 shows the distribution of differences for the first LDH tests, and indicates that the distribution was approximately normal. No explanation for the slight peaks on either side can be given. The standard deviation of this distribution was 18.8 mU/ml, from which it can be concluded that for 95% of the individual cases the difference was less than 37.6 mU/ml (two standard deviations). The standard deviations for the difference distribution ofthe constituents tested are shown in Table 3. In general, these deviations are ofthe order ofthe standard deviations ofthe test measurements, indicating that in individual cases the effect of transmission by pneumatic tube will be negligible or slight compared with the unavoidable variations inherent in the testing procedures.
Table 1. Summary of Equipment and Methodology Laboratory Procedure
Methodology
Standard Deviation
First test Sodium (Na + ) Potassium (K + ) Chloride (CI") Carbon dioxide (C0 2 ) Total protein (TP) Albumin (Alb) Calcium (Ca) Glucose (Glu) Creatinine (Cr) Total bilirubin (TB) Alkaline phosphatase (alk. P) Aspartate transaminase (SGOT) Lactic dehydrogenase (LDH) Acid phosphatase (acid P) Uric acid (uric A) Leukocyte count Erythrocyte count Hemoglobin (Hb) Hematocrit (Hct) Prothrombin time (PT) Partial thromboplastin time (PTT)
SMA 12/60 Flame emission Flame emission Mercuric thiocyanate Tris-buffered cresol red Biuret Bromcresol green Cresolphthalein complexone Glucose oxidase (BMC) Alkaline picrate Jendrassik-Grof Para-nitrophenyl phosphate
±0.9 mEq/1 ±0.06 mEq/1 ±0.9 mEq/1 ±1.0 mEq/1 ±0.08 g/dl ±0.07 g/dl ±0.16 mg/dl ±2.5 mg/dl ±0.05 mg/dl ±0.06 mg/dl ±4.0 mU/ml
MDH/NADH at 37 C Beckman TR
±3.3 mU/ml
Lactate to pyruvate at 37 c (Beckman) Alpha naphthyl phosphate (SK.F) Technicon AA II Phosphotungstate Coulter S Coulter reagents Coulter reagents Coulter reagents Coulter reagents MLA Electra 600 Dade thrombin, etc.
t7.0 mU/ml
Dade thrombin, etc.
tl.O mU/ml t0.12 mg/dl t0.4 x 107ml t0.07 x 107ml t0.2 g/dl 11.0% t1.7 sec t6.4 sec
Second test Beckman TR Lactate dehydrogenase (LDH) Aspartate transaminase (SGOT)
Lactate to pyruvate at 37 C (Beckman) MDH/NADH 37 C (Beckman)
±7.0 mU/ml ±1.7 mU/ml
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No breakage, spillage, or leakage occurred in any test. Table 2 shows the analytic results for the 21 constituents tested. The SGOT and LDH retest results are also included. The differences between means for the manually delivered and pneumatically delivered sample groups are expressed as percentages of the manually delivered means (column 6). Those results for which the t ratio was larger than 2, in column 8, indicate that the differences were significant at the 95%
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Table 2. Summary of Test Results
Test Na + K+
ciC02 TP Alb
Ca++
Retest SGOT LDH LDH
Units (SI)
106 111 112 95 114 114 114 114 114 112 114 112 115 63 129
mEq/1 (mmol/1) mEq/l (mmol/l) mEq/1 (mmol/l) mEq/l (mmol/l) g/dl (g/1) g/dl (mmol/l) mg/dl (mmol/l) mg/dl (mmol/l) mg/dl (mmol/l) mg/dl (mmol/l) mU/ml mU/ml mU/ml mU/ml mg/dl (mmol/l)
123
per //.I (1)
124 124 123 66 45 78 81 20
per/xl (1) gm/dl (mmol/l)
% sec (s) sec (s)
Mean (M anual) 139.6 4.28 102.5 25.9 7.20 4.44 9.46 89.5 1.01 .54 56.0 23.2 103.6 8.33 5.37
(SI)
(72) (0.68) (2.36) (4.92) (88.4) (9.2)
(0.32)
Mean (Pneumatic) (SI)
t Ratio
139.5 4.32 102.7 26.4 7.20 4.39 9.44 90.8 1.01 .56 56.2 25.1 111.8 8.33 5.33
-.03 .9 .2 2.1 .05 -1.2 -.3 1.4 .1 3.6 .2 8.3 8.0 0.0 .6
.5 1.9 2.4 3.7 .2 3.0 1.9 2.2 2.5 2.3 .4 3.1 4.7 0.0 1.0
(72) (0.676) (2.36) (4.99) (88.4) (9.6)
(0.31)
8.44 x 103
(8.44 x 109)
8.49 x 103
6
12
6
4.44 x 10 13.01 38.6 14.0 40.2
(4.44 x 10 ) (2.02) (0.3)
4.43 x 10 13.01 38.5 14.1 sec 39.0 sec
(2.02) (0.39)
95% Significance
Diff. Dev.
Yes Yes Yes Yes Yes Yes Yes Yes
.5
.9
.3 .03 .4 .5 3.0
1.0 .1 1.2 .3 2.3
Yes
Yes
mU/ml mU/ml
23.6 142.0
24.0 150.3
1.5 5.9
1.0 3.9
Yes
Yes
mU/ml
75% filled 145.9
50% filled 156.6
7.3
2.6
Yes
Yes
Comparison of the LDH values obtained from halffilled and 75%-filled tubes disclosed a t ratio of 2.6 and a difference of means of 7.3% (the half-filled group was higher), indicating that there is a measurable and statistically significant increase in values from serum from the half-filled containers on the order of the average shift of LDH values for all samples in the study (Table 2). Discussion Following the installation of a new pneumatic tube system, we investigated the effects of pneumatic transportation upon frequently performed laboratory tests ordered upon adult patients admitted to the hospital's medical and surgical wards. Lactate dehydrogenase activity and acid phosphatase activity were also analyzed because other studies have reported elevations in these values from specimens sent through the pneumatic tubes.2,5 We found that 14 of 15 chemical tests and six hematologic tests, compared with the precision of controls, were unaffected by pneumatic transport and could be safely transported through our pneumatic tube. We are aware of only one other study confirming the stability of the complete blood count.3
Only the results of LDH activity from specimens transported through the pneumatic tube showed a significant difference in the means beyond the precision of the test. At least two previous studies recounted elevations in LDH activity artifactually induced by pneumatic transport.2,5 In these investigations the mean increases in LDH values of pneumatically transported blood were 70%2 and 48%,5 while the increase in our pneumatically transported specimens was only 6%. The erythrocyte was undoubtedly the source of increased serum LDH activity. Its intraerythrocytic concentration exceeds plasma activity by at least 1,000 times, and hemolysis of only 0.1% of erythrocytes in a specimen will increase LDH activity by at least 18%.' Trauma to erythrocytes in the pneumatic tube system is postulated to occur with abrupt changes in direction at high speed or during rapid deceleration.4 The amount of movement of blood within the tube during transport affects erythrocytic damage. Our studies and the work of others confirmed that the least differences from control values of LDH occur in those tubes that are more than half full.4,5 Although pneumatic transport increased the mean difference of LDH beyond the limits of precision of the test, the mean increase was only 6%, and for total LDH activity is probably clinically insignificant.
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Glu Cr TB Alk. P SGOT LDH Acid P Uric A Leukocyte count Erythrocyte count Hb Hct PT FIT
N
% Difference
A.J.CP. • September 1978
WEAVER ET AL.
404
an
/
\
1
/ JU
/ \
1 1 1
O
FIG. 2. Histiogram showing Ihe parametric distribution of differences in lactate dehydrogenase activity.
O
/
t.V
1
1 1 I 1 \ I \ \ \ \
1
in
1 / f~~"*t
>
•-J
/
. \
^
^ \
1 1 60 50 negative
*l 40
30
20
10
0
10
20
30
40
50
60 positive
LDH Differences: mU/ml
Because of the wide distribution of LDH in the body, the enzyme is used in our hospital only in conjunction with the determination of its isoenzymes and is not a stat test. Since the effect of mechanical transportation upon isoenzymes of LDH was not tested, we do not Table 3. Standard Deviation of the Difference Distribution Test Na + K+
ci-
co
TP 2 Alb Ca Glu Cr TB Alk. P SGOT LDH Acid P Uric A Leukocyte count Erythrocyte count Hb Hct PT PTT
Standard Deviation 1.0 .21 .77 1.4 .18 .18 .16 6.3 .057 .088 2.8 6.5 18.8 1.2 .38 .57 .15 .31 1.4 1.6 3.5
mEq/1 mEq/1 mEq/1 mEq/1 g/dl g/dl mg/dl mg/dl mg/dl mg/dl mU/ml mU/ml mU/ml mU/ml mg/dl x 103/ml x 106/ml g/dl
%
sec sec
transport blood for LDH determinations within the pneumatic tube. The only study not recording elevated LDH activities in pneumatically transported specimens was that of Pragay and associates.4 Comparing our system with that used by Pragay, we could not explain the slight increase in our LDH values by the distance the specimen traveled (further in Pragay's study) or the method of deceleration (both use reversed air pressure). Since the carrier speed in our system is 5 feet per sec (1.5 meters/second) faster than that in Pragay's system, we can not exculpate this variable; however, the conditions under which the tests were conducted may be of even greater importance in explaining the differences in LDH values. -Whereas Pragay used healthy volunteers whose blood was drawn under controlled conditions to at least 80% of the capacity of the evacuated test tube,4 our venipuncturists drew blood in the routine manner from hospitalized patients and outpatients during routine working hours. They expended no special effort to assure that the evacuated test tubes were 80% filled. Even in Pragay's study LDH activity increased when the tubes were only 50% filled4; therefore, it seems reasonable that incompletely filled Vacutainer tubes were at least partially responsible for the slightly elevated LDH activity in pneumatically transported specimens in our study. We stress that if the LDH
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1 1 1
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LABORATORY SUGGESTIONS
ported specimens from patients with hematologic diseases and those specimens from subjects without hematologic diseases.5 The speed and convenience of the pneumatic transport system can be used effectively for the transport of routine and stat samples to the laboratory without compromising clinical diagnosis; it permits prompt dispatch of specimens to the laboratory and more efficient use of venipuncturists. References 1. Laessig RH, Hassemer DJ, Pasket TA, et al: The effects of 0.1 and 1.0 percent erythrocytes and hemolysis on serum chemistry values. Am J Clin Pathol 66:639-644, 1976 2. McClellan EK, Nakamura RM, Haas W, et al: Effect of pneumatic tube transport system on the validity of determinations in blood chemistry. Am J Clin Pathol 42:152-155, 1964 3. Nosanchuk JS: Automated transport of clinical laboratory specimens by a new air-transport tube system. Am J Clin Pathol 67:204, 1977 4. Pragay DA. Edwards L, Toppin RR, et al: Evaluation of an improved pneumatic tube system suitable for transportation of blood specimens. Clin Chem 20:57-60, 1974 5. Steige H, Jones JD: Evaluation of pneumatic tube system for delivery of blood specimens. Clin Chem 17:1160-1164, 1971
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activity is to be determined on pneumatically transported blood, then special attention should be exercised to assure at least 80% filling of evacuated test tubes. Besides evaluating the effect of pneumatic transportation upon biologic assays, one should assess the carriers used in a pneumatic tube so that they are designed or may be modified to minimize movement of the tubes within the carrier and preclude breakage. To date we have yet to experience breakage or uncorking of a test tube in our system. We did not evaluate the effect of pneumatic transportation upon blood typing, the detection of irregular antibodies, sedimentation rates, arterial blood gases and pH, or urinalysis. A preliminary report discloses that samples for these determinations, excluding blood for cross-matching, in which weak serum antibodies were lost, may be safely sent through pneumatic tubes.3 Although we did not correlate the patients' diseases with the values obtained after transport through the pneumatic tube, Steige and Jones found no difference between the magnitudes of increase of either LDH activity or plasma hemoglobin in pneumatically trans-
405
M O D E R N , W E L L - E Q U I P P E D hospitals use pneumatic-tube systems to speed the flow of requisitions, results, messages, and small supply items. The potential uses of these fast delivery systems for sending body-fluid specimens for analysis have produced interest and controversy. 2 - 5 Before sending specimens through a pneumatic tube, two criteria must be fulfilled: the results of analysis of blood specimens must be unaffected by their journey, and the journey must be safe for the specimen to preclude contamination of the system by breakage. Two previous studies demonstrated that serum or plasma sodium, chloride, carbon dioxide, inorganic phosphorus, calcium, urea, uric acid, glucose, alanine aminotransferase, aspartate aminotransferase, creatinine, total protein, fibrinogen, hemoglobin, and bilirubin could be safely transported through existing pneumatic tubes but that values for lactate dehydrogenase (LDH), potassium, acid phosphatase and serum hemoglobin were artifactually elevated. A recent abReceived April 6, 1977; received revised manuscript May 23, 1977; accepted for publication May 23, 1977. Address reprint requests to Dr. Weaver: Williamsport Hospital, 777 Rural Ave., Williamsport, Pennsylvania 17701.
Williamsport Hospital and Friesen International, Inc., Williamsport, Pennsylvania
stracted account reported statistically significant differences in LDH, aspartate aminotransferase, and glucose. 2 - 5 On the other hand, using a pilot system, another evaluation of a pneumatic-tube system reported no difference in values of acid phosphatase, potassium, aspartate aminotransferase, glucose, or lactic dehydrogenase in specimens delivered by pneumatic and manual methods. 4 Others' experience with pneumatic transportation of specimens reveals that each system should be assessed for the effect of pneumatic transportation upon chemical constituents measured. We propose to report upon our results from the transportation of blood specimens through a pneumatic-tube system. The tests were conducted under routine working conditions in a hospital laboratory. Materials and Methods The pneumatic-tube system used at the Williamsport Hospital is a Trans-Logic 200.* Carriers are directed through 4" diameter (10-cm) steel conduits to various stations throughout the hospital at speeds of as much as 25 feet/sec (7.6 meters/sec). The blowers and transfer units are controlled and monitored by a central processor that has stored the required transaction data. The computer directs carriers to their destination via the shortest, most direct route available. The carriers are constructed of a translucent plastic with a 15-inch (37.5-cm) inside length and have a nominal load capacity of 2.75 lb (1.25 kg). Molded foam-rubber inserts prevent movement of collection tubes within the carrier (Fig. 1). The carrier can be inserted into the system in either direction but cannot be inserted unless the two sections are securely latched. Samples transported by the system for this study originated either at the outpatient department or at one of the inpatient areas. The outpatient samples were dispatched from the laboratory pneumatic station and * Powers Regulator Corp. Colorado.
Transitube Division, Denver,
0002-9173/78/0900/0400 $00.75 © American Society of Clinical Pathologists
400
Downloaded from http://ajcp.oxfordjournals.org/ by guest on March 19, 2016
Weaver, Don K., Miller, Dorland, Leventhal, Edwin A., and Tropeano, Vincent. Evaluation of a computer directed pneumatic tube system for pneumatic transport of blood specimens. Am J Clin Pathol 70: 400-405, 1978. The results of sending specimens through a computerized pneumatic airtransport system and manually delivering specimens were compared for 15 chemical tests and six hematologic procedures. All specimens were collected from inpatients and outpatients into evacuated glass containers. The specimens traversed a maximum of 829 feet (253 meters) involving 16 bends and eight transfer units at 25 feet/second (7.6 meters/second). Only the activity of lactate dehydrogenase exceeded the precision of the test in pneumatically transported specimens. Ruptured erythrocytes in incompletely filled vacuum tubes were the likely source of the increased lactate dehydrogenase activity. Neither the serum sodium, potassium, chloride, carbon dioxide, total protein, albumin, calcium, glucose, creatinine, total bilirubin, alkaline phosphatase, aspartate transaminase, acid phosphatase, uric acid, leukocyte count, erythrocyte count, hemoglobin, hematocrit, nor the prothrombin time and partial thromboplastin time were affected by pneumatic transport. It is concluded that the pneumatic system tested provides a safe, efficient method of transporting the blood specimens tested. (Key words: Pneumatic transport; Blood specimens.)
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401
FIG. I. Opened plastic transport container lined with foamrubber inserts.
Sample and Test Methods All blood was obtained from patients at the Williamsport Hospital, a 370-bed general hospital in Williamsport, Pennsylvania. Duplicate blood samples were drawn from inpatients during routine morning and afternoon collections and from outpatients whenever they arrived at the laboratory. Stat tests and requests from patients in the nursery and critical care units were excluded from the study. Each blood sample was labeled with the patient's name, hospital number, date drawn, and time drawn. The venipuncturist coded the two blood specimens with a prestuck label A, B, or C; the remaining label was applied to the request slip. The venipuncturist randomly sent one labeled specimen (A, B, or C) through the pneumatic tube and handcarried the other specimen to the laboratory. Specimens from hospitalized patients came from any of five floors; therefore, the distances traveled by the specimens in the pneumatic tube varied. Specimens drawn from outpatients traveled from the laboratory to the most distant receiving station and back to the laboratory, traversing roughly twice the distance traversed by specimens sent from inpatient wards. A test coordinator, unassociated with the clinical laboratory, received the samples, recorded the pertinent data, coded the specimens, and distributed all manually and pneumatically transmitted samples promptly to the laboratory personnel, who were unaware of the source of the samples. Blood samples sent to Chemistry were centrifuged, and 15 serum chemical constituents were determined (Table 1). Blood received in Hematology was mixed, and the Coulter S was used to determine the leukocyte count, erythrocyte count, hemoglobin, and hematocrit.
Prothrombin and partial thromboplastin times were measured in an ML A Electra 500 (Table 1). Test results were returned to the test coordinator, who verified the correctness of the identifying information (patient name, test number, and appropriate code letter). The test results were matched to original work papers to indicate which specimen was test and which was control. A change in the source of reagents for lactate dehydrogenase and aspartate transaminase necessitated a second study of these enzymes five months after the initial test. The design of the test was identical to that of the previous study except that the Beckman TR replaced the SMA 12/60 to determine aspartate transaminase (Table 1). The effect of movement of blood in the evacuated container was tested by drawing blood from each of 20 outpatients into two 10-ml Monojet evacuated glass tubes. One tube wasfilledto its capacity; the other tube was filled to half its capacity. Before the blood clotted, both containers were sent through the pneumatic tube from the laboratory office to the end of the system and returned. Following prompt centrifugation and separation of the serum from the clot, lactate dehydrogenase activity of both samples was determined. The standard deviation for each test was obtained from results of lyophilized pooled serum controls. Methods of Data Analysis Because the data were collected from paired samples (one of each pair delivered manually and one delivered pneumatically), the t ratio was chosen as the quantity for determining statistical significance. The t ratio represents the mean difference of all pairs in the sample group divided by the standard error of the differences in the sample group. In Student's t distribution a t ratio greater than 2 represents 95% confidence that the mean difference is not zero. Sample groups of the type studied here do not usually fit Student's t distribution precisely; however, the differences are not considered
Downloaded from http://ajcp.oxfordjournals.org/ by guest on March 19, 2016
traveled through 829.84 feet (253 meters) of straight tube, 16 bends, and eight transfer units before returning to the laboratory. Samples from inpatient areas traveled a distance approximately 50% of that traversed by the outpatient specimens.
402
WEAVER ET AL.
significant for the purposes being investigated. After establishing which of the test results had a non-zero difference, with 95% confidence, the differences were compared with the standard deviation for the respective test methods and the equipment used. Differences of less than one standard deviation were judged not significant for clinical diagnostic purposes. Results
confidence level. In all cases but the two LDH tests, the differences were less than one standard deviation ofthe test method and were within the precision limits ofthe test. Figure 2 shows the distribution of differences for the first LDH tests, and indicates that the distribution was approximately normal. No explanation for the slight peaks on either side can be given. The standard deviation of this distribution was 18.8 mU/ml, from which it can be concluded that for 95% of the individual cases the difference was less than 37.6 mU/ml (two standard deviations). The standard deviations for the difference distribution ofthe constituents tested are shown in Table 3. In general, these deviations are ofthe order ofthe standard deviations ofthe test measurements, indicating that in individual cases the effect of transmission by pneumatic tube will be negligible or slight compared with the unavoidable variations inherent in the testing procedures.
Table 1. Summary of Equipment and Methodology Laboratory Procedure
Methodology
Standard Deviation
First test Sodium (Na + ) Potassium (K + ) Chloride (CI") Carbon dioxide (C0 2 ) Total protein (TP) Albumin (Alb) Calcium (Ca) Glucose (Glu) Creatinine (Cr) Total bilirubin (TB) Alkaline phosphatase (alk. P) Aspartate transaminase (SGOT) Lactic dehydrogenase (LDH) Acid phosphatase (acid P) Uric acid (uric A) Leukocyte count Erythrocyte count Hemoglobin (Hb) Hematocrit (Hct) Prothrombin time (PT) Partial thromboplastin time (PTT)
SMA 12/60 Flame emission Flame emission Mercuric thiocyanate Tris-buffered cresol red Biuret Bromcresol green Cresolphthalein complexone Glucose oxidase (BMC) Alkaline picrate Jendrassik-Grof Para-nitrophenyl phosphate
±0.9 mEq/1 ±0.06 mEq/1 ±0.9 mEq/1 ±1.0 mEq/1 ±0.08 g/dl ±0.07 g/dl ±0.16 mg/dl ±2.5 mg/dl ±0.05 mg/dl ±0.06 mg/dl ±4.0 mU/ml
MDH/NADH at 37 C Beckman TR
±3.3 mU/ml
Lactate to pyruvate at 37 c (Beckman) Alpha naphthyl phosphate (SK.F) Technicon AA II Phosphotungstate Coulter S Coulter reagents Coulter reagents Coulter reagents Coulter reagents MLA Electra 600 Dade thrombin, etc.
t7.0 mU/ml
Dade thrombin, etc.
tl.O mU/ml t0.12 mg/dl t0.4 x 107ml t0.07 x 107ml t0.2 g/dl 11.0% t1.7 sec t6.4 sec
Second test Beckman TR Lactate dehydrogenase (LDH) Aspartate transaminase (SGOT)
Lactate to pyruvate at 37 C (Beckman) MDH/NADH 37 C (Beckman)
±7.0 mU/ml ±1.7 mU/ml
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No breakage, spillage, or leakage occurred in any test. Table 2 shows the analytic results for the 21 constituents tested. The SGOT and LDH retest results are also included. The differences between means for the manually delivered and pneumatically delivered sample groups are expressed as percentages of the manually delivered means (column 6). Those results for which the t ratio was larger than 2, in column 8, indicate that the differences were significant at the 95%
A.J.C.P. • September 1978
LABORATORY SUGGESTIONS
Vol. 70 • No. 3
403
Table 2. Summary of Test Results
Test Na + K+
ciC02 TP Alb
Ca++
Retest SGOT LDH LDH
Units (SI)
106 111 112 95 114 114 114 114 114 112 114 112 115 63 129
mEq/1 (mmol/1) mEq/l (mmol/l) mEq/1 (mmol/l) mEq/l (mmol/l) g/dl (g/1) g/dl (mmol/l) mg/dl (mmol/l) mg/dl (mmol/l) mg/dl (mmol/l) mg/dl (mmol/l) mU/ml mU/ml mU/ml mU/ml mg/dl (mmol/l)
123
per //.I (1)
124 124 123 66 45 78 81 20
per/xl (1) gm/dl (mmol/l)
% sec (s) sec (s)
Mean (M anual) 139.6 4.28 102.5 25.9 7.20 4.44 9.46 89.5 1.01 .54 56.0 23.2 103.6 8.33 5.37
(SI)
(72) (0.68) (2.36) (4.92) (88.4) (9.2)
(0.32)
Mean (Pneumatic) (SI)
t Ratio
139.5 4.32 102.7 26.4 7.20 4.39 9.44 90.8 1.01 .56 56.2 25.1 111.8 8.33 5.33
-.03 .9 .2 2.1 .05 -1.2 -.3 1.4 .1 3.6 .2 8.3 8.0 0.0 .6
.5 1.9 2.4 3.7 .2 3.0 1.9 2.2 2.5 2.3 .4 3.1 4.7 0.0 1.0
(72) (0.676) (2.36) (4.99) (88.4) (9.6)
(0.31)
8.44 x 103
(8.44 x 109)
8.49 x 103
6
12
6
4.44 x 10 13.01 38.6 14.0 40.2
(4.44 x 10 ) (2.02) (0.3)
4.43 x 10 13.01 38.5 14.1 sec 39.0 sec
(2.02) (0.39)
95% Significance
Diff. Dev.
Yes Yes Yes Yes Yes Yes Yes Yes
.5
.9
.3 .03 .4 .5 3.0
1.0 .1 1.2 .3 2.3
Yes
Yes
mU/ml mU/ml
23.6 142.0
24.0 150.3
1.5 5.9
1.0 3.9
Yes
Yes
mU/ml
75% filled 145.9
50% filled 156.6
7.3
2.6
Yes
Yes
Comparison of the LDH values obtained from halffilled and 75%-filled tubes disclosed a t ratio of 2.6 and a difference of means of 7.3% (the half-filled group was higher), indicating that there is a measurable and statistically significant increase in values from serum from the half-filled containers on the order of the average shift of LDH values for all samples in the study (Table 2). Discussion Following the installation of a new pneumatic tube system, we investigated the effects of pneumatic transportation upon frequently performed laboratory tests ordered upon adult patients admitted to the hospital's medical and surgical wards. Lactate dehydrogenase activity and acid phosphatase activity were also analyzed because other studies have reported elevations in these values from specimens sent through the pneumatic tubes.2,5 We found that 14 of 15 chemical tests and six hematologic tests, compared with the precision of controls, were unaffected by pneumatic transport and could be safely transported through our pneumatic tube. We are aware of only one other study confirming the stability of the complete blood count.3
Only the results of LDH activity from specimens transported through the pneumatic tube showed a significant difference in the means beyond the precision of the test. At least two previous studies recounted elevations in LDH activity artifactually induced by pneumatic transport.2,5 In these investigations the mean increases in LDH values of pneumatically transported blood were 70%2 and 48%,5 while the increase in our pneumatically transported specimens was only 6%. The erythrocyte was undoubtedly the source of increased serum LDH activity. Its intraerythrocytic concentration exceeds plasma activity by at least 1,000 times, and hemolysis of only 0.1% of erythrocytes in a specimen will increase LDH activity by at least 18%.' Trauma to erythrocytes in the pneumatic tube system is postulated to occur with abrupt changes in direction at high speed or during rapid deceleration.4 The amount of movement of blood within the tube during transport affects erythrocytic damage. Our studies and the work of others confirmed that the least differences from control values of LDH occur in those tubes that are more than half full.4,5 Although pneumatic transport increased the mean difference of LDH beyond the limits of precision of the test, the mean increase was only 6%, and for total LDH activity is probably clinically insignificant.
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Glu Cr TB Alk. P SGOT LDH Acid P Uric A Leukocyte count Erythrocyte count Hb Hct PT FIT
N
% Difference
A.J.CP. • September 1978
WEAVER ET AL.
404
an
/
\
1
/ JU
/ \
1 1 1
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FIG. 2. Histiogram showing Ihe parametric distribution of differences in lactate dehydrogenase activity.
O
/
t.V
1
1 1 I 1 \ I \ \ \ \
1
in
1 / f~~"*t
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•-J
/
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^
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1 1 60 50 negative
*l 40
30
20
10
0
10
20
30
40
50
60 positive
LDH Differences: mU/ml
Because of the wide distribution of LDH in the body, the enzyme is used in our hospital only in conjunction with the determination of its isoenzymes and is not a stat test. Since the effect of mechanical transportation upon isoenzymes of LDH was not tested, we do not Table 3. Standard Deviation of the Difference Distribution Test Na + K+
ci-
co
TP 2 Alb Ca Glu Cr TB Alk. P SGOT LDH Acid P Uric A Leukocyte count Erythrocyte count Hb Hct PT PTT
Standard Deviation 1.0 .21 .77 1.4 .18 .18 .16 6.3 .057 .088 2.8 6.5 18.8 1.2 .38 .57 .15 .31 1.4 1.6 3.5
mEq/1 mEq/1 mEq/1 mEq/1 g/dl g/dl mg/dl mg/dl mg/dl mg/dl mU/ml mU/ml mU/ml mU/ml mg/dl x 103/ml x 106/ml g/dl
%
sec sec
transport blood for LDH determinations within the pneumatic tube. The only study not recording elevated LDH activities in pneumatically transported specimens was that of Pragay and associates.4 Comparing our system with that used by Pragay, we could not explain the slight increase in our LDH values by the distance the specimen traveled (further in Pragay's study) or the method of deceleration (both use reversed air pressure). Since the carrier speed in our system is 5 feet per sec (1.5 meters/second) faster than that in Pragay's system, we can not exculpate this variable; however, the conditions under which the tests were conducted may be of even greater importance in explaining the differences in LDH values. -Whereas Pragay used healthy volunteers whose blood was drawn under controlled conditions to at least 80% of the capacity of the evacuated test tube,4 our venipuncturists drew blood in the routine manner from hospitalized patients and outpatients during routine working hours. They expended no special effort to assure that the evacuated test tubes were 80% filled. Even in Pragay's study LDH activity increased when the tubes were only 50% filled4; therefore, it seems reasonable that incompletely filled Vacutainer tubes were at least partially responsible for the slightly elevated LDH activity in pneumatically transported specimens in our study. We stress that if the LDH
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1 1 1
Vol. 70 • No. 3
LABORATORY SUGGESTIONS
ported specimens from patients with hematologic diseases and those specimens from subjects without hematologic diseases.5 The speed and convenience of the pneumatic transport system can be used effectively for the transport of routine and stat samples to the laboratory without compromising clinical diagnosis; it permits prompt dispatch of specimens to the laboratory and more efficient use of venipuncturists. References 1. Laessig RH, Hassemer DJ, Pasket TA, et al: The effects of 0.1 and 1.0 percent erythrocytes and hemolysis on serum chemistry values. Am J Clin Pathol 66:639-644, 1976 2. McClellan EK, Nakamura RM, Haas W, et al: Effect of pneumatic tube transport system on the validity of determinations in blood chemistry. Am J Clin Pathol 42:152-155, 1964 3. Nosanchuk JS: Automated transport of clinical laboratory specimens by a new air-transport tube system. Am J Clin Pathol 67:204, 1977 4. Pragay DA. Edwards L, Toppin RR, et al: Evaluation of an improved pneumatic tube system suitable for transportation of blood specimens. Clin Chem 20:57-60, 1974 5. Steige H, Jones JD: Evaluation of pneumatic tube system for delivery of blood specimens. Clin Chem 17:1160-1164, 1971
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activity is to be determined on pneumatically transported blood, then special attention should be exercised to assure at least 80% filling of evacuated test tubes. Besides evaluating the effect of pneumatic transportation upon biologic assays, one should assess the carriers used in a pneumatic tube so that they are designed or may be modified to minimize movement of the tubes within the carrier and preclude breakage. To date we have yet to experience breakage or uncorking of a test tube in our system. We did not evaluate the effect of pneumatic transportation upon blood typing, the detection of irregular antibodies, sedimentation rates, arterial blood gases and pH, or urinalysis. A preliminary report discloses that samples for these determinations, excluding blood for cross-matching, in which weak serum antibodies were lost, may be safely sent through pneumatic tubes.3 Although we did not correlate the patients' diseases with the values obtained after transport through the pneumatic tube, Steige and Jones found no difference between the magnitudes of increase of either LDH activity or plasma hemoglobin in pneumatically trans-
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