CORRESPONDENCE AND CORRECTIONS Inaccurate Results of Urine Dipstick Tests To the Editor:—I read with interest Cohen and Spiegel's1 article about falsepositive and false-negative results of urine dipstick examinations. Conspicuous by its absence is any mention of the role of quality control in detecting deterioration of reagents. This article presents the strongest argument I have seen against allowing laboratory tests to be performed by those not well versed in laboratory practice. It also argues against the Health Care Financing Administration's pro-
posed CLIA '88 regulations that would exempt "waivered" tests from quality control requirements.2 Proper quality control procedures are necessary "to avoid prompting needless evaluation of glucosuria or delaying detection of important causes of microscopic hematuria." EVAN M. CADOFF, M.D.
Department of Pathology Robert Wood Johnson Medical School New Brunswick, New Jersey
References 1. Cohen HT, Spiegel DM. Air-exposed urine dipsticks give false-positive results for glucose and false-negative results for blood. Am J Clin Pathol 1991;96:398400. 2. Department of Health and Human Services, Health Care Financing Administration. Regulations implementing the Clinical Laboratory Improvement Amendments of 1988. 22 CFR, part 493.
To the Editor:—Dr. Cadoff raises an important point. Certainly, if urine dipsticks were only used in accredited clinical laboratories where quality control measures were taken, the likelihood of inaccuracies from air exposure would be minimal. However, because urine dipsticks can provide valuable information simply and rapidly (and can even be used by patients to screen their own urine), we are reluctant to support any argument aimed
at limiting their availability and instead would recommend increasing awareness of their potential problems. Our study provides the missing rationale for resealing urine dipstick containers1 and we hope it will serve best to educate and reinforce this need rather than justify increased regulation. HERBERT T. COHEN, M.D. DAVID M. SPIEGEL, M.D.
Section of Nephrology Department of Medicine University of Chicago Medical Center Chicago, Illinois Reference , Cohen HT, Spiegel DM. Air-exposed urine dipsticks give false-positive results for glucose and false-negative results for blood. Am J Clin Pathol 1991;96:398400.
Monocyte Count in Coulter STKS and MAXM To the Editor:—Warner and Reardon' recently published an evaluation of the Coulter STKS, a complete CBC analyzer using a flow cytometric method dedicated to the WBC differential. The differential results of the Coulter STKS correlated well with the optical reference method. However, the monocyte correlation suggested that the monocyte population was underestimated; this point was confirmed by the results of Fialon and associates.2 Furthermore, several studies were performed to compare the WBC differential results given by several instruments; it was generally shown that all instruments, Coulter STKS3 and Coulter VCS, 45 as well as Technicon HI, 3 " 5 underestimated the monocyte count according to the optical method used as a reference; the TOA NE 80003'4 even gave a very poor correlation with the optical differential. Those data are listed in Table 1.
TABLE 1. MONOCYTE CORRELATION (INSTRUMENTS vs. OPTICAL METHOD) IN SEVERAL PAPERS RECENTLY PUBLISHED FOR COULTER STKS AND VCS, TECHNICON HI, AND TOA NE 8000 Instrument Coulter STKS
Coulter VCS
Correlation Coefficient 0.764 0.734 0.744
—
0.871 Technicon H1
TOA NE 8000
— 0.766 0.701 0.327 0.237
Equation of the Regression Line y= y = y= y= y= y= y= y= y= y=
0.64x + 0.65x+ 0.68x+ 0.75x+ 0.76x 0.75x + 0.86x 0.78x + 0.27x + 0.24x+
2.0 1.4 1.3 1.0 0.8 2.0 0.6 2.9 3.3 1.2
Reference (2) (1) (3) (5) (4) (5) (4) (3) (3) (4)
In all papers, the monocytes were expressed and analyzed as percentages.
Coulter Corporation recently reviewed this point, producing a new STKS and MAXM algorithm for monocyte measurement. We compared the STKS ex-
269
perience of our three laboratories by evaluating the monocyte results given by a Coulter MAXM (F.P.), a Coulter STKS working with the new algorithm (P.F.),
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The Authors' Reply
posed CLIA '88 regulations that would exempt "waivered" tests from quality control requirements.2 Proper quality control procedures are necessary "to avoid prompting needless evaluation of glucosuria or delaying detection of important causes of microscopic hematuria." EVAN M. CADOFF, M.D.
Department of Pathology Robert Wood Johnson Medical School New Brunswick, New Jersey
References 1. Cohen HT, Spiegel DM. Air-exposed urine dipsticks give false-positive results for glucose and false-negative results for blood. Am J Clin Pathol 1991;96:398400. 2. Department of Health and Human Services, Health Care Financing Administration. Regulations implementing the Clinical Laboratory Improvement Amendments of 1988. 22 CFR, part 493.
To the Editor:—Dr. Cadoff raises an important point. Certainly, if urine dipsticks were only used in accredited clinical laboratories where quality control measures were taken, the likelihood of inaccuracies from air exposure would be minimal. However, because urine dipsticks can provide valuable information simply and rapidly (and can even be used by patients to screen their own urine), we are reluctant to support any argument aimed
at limiting their availability and instead would recommend increasing awareness of their potential problems. Our study provides the missing rationale for resealing urine dipstick containers1 and we hope it will serve best to educate and reinforce this need rather than justify increased regulation. HERBERT T. COHEN, M.D. DAVID M. SPIEGEL, M.D.
Section of Nephrology Department of Medicine University of Chicago Medical Center Chicago, Illinois Reference , Cohen HT, Spiegel DM. Air-exposed urine dipsticks give false-positive results for glucose and false-negative results for blood. Am J Clin Pathol 1991;96:398400.
Monocyte Count in Coulter STKS and MAXM To the Editor:—Warner and Reardon' recently published an evaluation of the Coulter STKS, a complete CBC analyzer using a flow cytometric method dedicated to the WBC differential. The differential results of the Coulter STKS correlated well with the optical reference method. However, the monocyte correlation suggested that the monocyte population was underestimated; this point was confirmed by the results of Fialon and associates.2 Furthermore, several studies were performed to compare the WBC differential results given by several instruments; it was generally shown that all instruments, Coulter STKS3 and Coulter VCS, 45 as well as Technicon HI, 3 " 5 underestimated the monocyte count according to the optical method used as a reference; the TOA NE 80003'4 even gave a very poor correlation with the optical differential. Those data are listed in Table 1.
TABLE 1. MONOCYTE CORRELATION (INSTRUMENTS vs. OPTICAL METHOD) IN SEVERAL PAPERS RECENTLY PUBLISHED FOR COULTER STKS AND VCS, TECHNICON HI, AND TOA NE 8000 Instrument Coulter STKS
Coulter VCS
Correlation Coefficient 0.764 0.734 0.744
—
0.871 Technicon H1
TOA NE 8000
— 0.766 0.701 0.327 0.237
Equation of the Regression Line y= y = y= y= y= y= y= y= y= y=
0.64x + 0.65x+ 0.68x+ 0.75x+ 0.76x 0.75x + 0.86x 0.78x + 0.27x + 0.24x+
2.0 1.4 1.3 1.0 0.8 2.0 0.6 2.9 3.3 1.2
Reference (2) (1) (3) (5) (4) (5) (4) (3) (3) (4)
In all papers, the monocytes were expressed and analyzed as percentages.
Coulter Corporation recently reviewed this point, producing a new STKS and MAXM algorithm for monocyte measurement. We compared the STKS ex-
269
perience of our three laboratories by evaluating the monocyte results given by a Coulter MAXM (F.P.), a Coulter STKS working with the new algorithm (P.F.),
Downloaded from http://ajcp.oxfordjournals.org/ by guest on June 7, 2016
The Authors' Reply
