648
PLANNING CASE-FINDING ACTIVITIES FOR A COMMUNITY HYPERTENSION-CONTROL PROGRAM* SYLVIA WASSERTHEIL-SMOLLER, Ph.D. Associate Professor, Department of Community Health
M. DONALD BLAUFOX, M.D., Ph.D. Associate Professor of Medicine and Radiology Albert Einstein College of Medicine Bronx, N.Y.
R
ECENT data 1,2,7 indicate that among those persons who had at one time been informed by their doctor that they had high blood pressure, only about half of the blacks and a little more than one third of the whites now are receiving appropriate therapy. Younger individuals in all of the race and sex groups are less likely to be receiving treatment for their hypertension, and if they are under treatment are less likely to be treated adequately. The importance of identifying and following the younger individuals is especially clear in view of these facts and in view of the prolonged impact that hypertension will have in the younger group. When we discuss the planning of case-finding activities, we must at the same time plan facilities for follow-up or treatment. Case finding without adequate planning for long-term treatment not only fails to reduce the impact of hypertension in the community, but also creates unrelieved anxiety in newly discovered patients. Thus, to be successful, case finding must be approached by working backward from a knowledge of the available capacity for follow-up treatment. For systematic planning of case finding it is necessary to have certain essential information so that we may calculate how many persons may be screened in order to yield a number of hypertensive patients that will neither overburden the available treatment and follow-up facilities nor underutilize them. *Presented in a panel, Case Finding, as part of a Conference on Developing and Managing Community Programs for the Control of Hypertension held by the New York Metropolitan Regional Medical Program at the New York Academy of Medicine April 15, 1975. This research was supported in part by Contract No. 1 HV22931 from the National Heart and Lung Institute, Bethesda, Md.
Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
649
The expected yield for treatment will depend on such factors as the following: 1) The definition of hypertension 2) The demographic composition of the target population 3) The prevalence rate for a population with that composition 4) The number of patients lost at different stages of the case-finding and follow-up procedures The first decision to be made is where and how the screening will take place. One may decide to do saturation screening. In that case, a target population such as a census tract, a housing development, or an industrial population would be selected, and an attempt would be made to screen everyone in it. The yield and loss to follow-up in such an undertaking may be quite different from that obtained in casual or opportunistic screening. In casual or opportunistic screening a station may be set up at a convenient location at which screening for hypertension would be made available to those who volunteer to have their pressures measured. It may be a single "one-shot" attempt, e.g., as at supermarkets, banks, or street corners on a specific day. Or casual screening may be conducted as a continued effort in a fixed location, e.g., a pharmacy or dentist's office.3 Proponents of screening for high blood pressure in pharmacies4 base their approach on the fact that in economically depressed areas the pharmacist is usually the last to move from the area and that people often look to the pharmacist as a source of medical care, making such a setting appropriate for screening. The problem with most of these programs is that a person's blood pressure is measured at the screening site and then there is little or no follow-up. The individual may be told that he or she has elevated blood pressure and should see a physician, but usually no attempt is made to determine whether, in fact, the patient did see a physician and whether his blood pressure has been brought under control. In fact, there is much evidence that diagnosed hypertensives are not treated adequately.5'6 More than half the patients with elevated blood pressure had previous knowledge of this and yet continued to have elevated pressures.7 Black individuals are less likely to have their hypertension under control than whites, men less likely than women. Further, persons who come voluntarily for screening tend to be older. Since the younger hypertensives may be at longer risk and may derive greater long-term benefits from therapy, they constitute an important group that may be missed through casual screening. This kind of Vol. 52, No. 6, July-August 1976
S. WASSERTHEIL-SMOLLER AND M. D. BLAUFOX
650
DIAGNOSIS
Screeninig results
Positive Netative Total
Sensitivity
Over-referral
Diseased a c
Nondiseased b d
Total a+b c 4d
a+c
b+d
a+b+c+d
a
Specitfcity
b b+d
a+,c 2 a+b
Under-referral
c c +d
screening, however, may be more economical and more practical in an individual situation. After choosing the appropriate screening method, the next major decision that has to be made is what blood-pressure point to use for the diagnosis of suspect hypertension. A variety of cut-off points have been used; it is important to have a precise, consistent definition. Some programs employ a systolic pressure of 140 mm. Hg or more or a diastolic pressure of 90 mm. Hg or more or both as diagnostic criteria and other programs use a systolic pressure of 160 mm. Hg or a diastolic of 95 mm. Hg or more or both.8 How does one decide which criteria to use for the diagnosis of hypertension in a screening program? It is desirable to have a screening test that is as specific as possible. The accompanying table illustrates the concepts of specificity, sensitivity, and over-referral and under-referral,9' which are utilized in this decision-making process. Specificity is the proportion of persons without the disease for whom the screening test is negative. It is determined by dividing the number of people who were screened as negative who did not have the disease by the total number of people who did not have the disease who were screened. Sensitivity is the proportion of persons with the disease for whom the screening test is positive. It is determined by dividing the number of people who were screened as positive who had the disease by the total number of people who had the disease who were screened. Over-referral is the proportion of people with positive screening results who are not diseased. It is determined by dividing the number of people who were screened as positive but did not have the disease by the total number of people who were screened as positive. Under-referral is the proportion of Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
651
people with negative screening results who had the disease. It is determined by dividing the number of people who were screened as negative but had the disease by the total number of people who were screened as negative. If the over-referral figure is large, facilities would be taxed unnecessarily, since many of the people who were judged positive in the first screening are not likely to be positive in the second screening. It would be better if the specificity were as high as possible. The ideal test would be negative for all well persons. One way to approach this goal is to have a two-stage screen with a higher cutoff point for the first screen than for the second. This was the decision reached in a major national program for hypertension detection and follow-up which shall be described briefly; it can serve as an example of how to use data effectively to plan case-finding efforts. The Hypertension Detection and Follow-Up Program (HDFP)2 is a 17-center national study to evaluate the efficacy of a community hypertension program. The Albert Einstein College of Medicine is a participant in the HDFP, with a center at Co-Op City, a middle-income housing development in the Bronx. The national program has screened 157,000 people between the ages of 30 and 69 years. This represents the largest screening effort for hypertension ever conducted in the United States, and the data on prevalence from this effort (to be published shortly) are the most recent figures available on the extent of this disease. At the New York Center in Co-Op City approximately 15,000 persons have been screened. In this program, saturation screening was employed at the Co-op City center. A target area was picked, each household within that area was enumerated to list all resident individuals, and a vigorous attempt was made to screen at home all age-eligible individuals, i.e., those 30 to 69 years of age. This program uses a two-stage screening based on -measurement of diastolic blood pressure alone. If an individual had a diastolic blood pressure of 95 mm. Hg or above at the home screening, he was asked to come to a specially established clinic for confirmation. If his diastolic blood pressure was 90 mm. Hg or above at the clinic screen, he was invited to become a participant in the program. There is a great variability in blood pressure. IO Among the people in the HDFP who were in the 95 to 104 mm. Hg stratum of blood pressure at home, 65% had less than 95 mm. Hg at the confirmation visit to the clinic; Vol. 52, No. 6, July-August 1976
652
S. WASSERTHEIL-SMOLLER AND M. D. BLAUFOX
90-104
105-114
115+
PESSUE Fig. 1. Estimated patient flow for two-stage screen. DEP -= diastolic blood pressure. DBP
-
DIASTOLIC BLOOD
45% had less than 90 mm. Hg at that repeat examination. Even among the people who had diastolic pressures of 115 mm. Hg or more at home, a full 10% had less than 90 mm. Hg at the clinic; only about one third of those with diastolic pressure greater than or equal to 115 mm. Hg at home showed this high level at the clinic.1 However, through specified cut-off Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
653
4.J
26%
be
QE E
0
+C00L *
21%
Al 13% 00
4-Jcu 0
~~~~~~~~~~~~~8%
4-i
WHBAK
Female Male BLACK
Fig. 2. Prevalence of elevated
(G
HT
Male Female WHITE
95 mm. Hg) diastolic blood pressure by race and sex.
points and the saturation method of screening, one can expect certain yields throughout the various screening stages, as illustrated in Figure 1, which is based on HDFP data. If one starts with a group of age-eligible individuals, N1, a certain number of these individuals, k1, will refuse to be screened at home. This will result in a group of persons, N2, who participate in a home screening (N2 is the N1 eligibles minus the k1 persons refusing home screening). Of those who are screened at home, a number of these individuals, k2, will have diastolic pressure less than 95 mm. Hg, leaving N3 = N2- k2 individuals eligible for a second screening at the clinic. Of these persons, a certain number, k3, will not show up at the clinic, leaving N4 = N3- k3 individuals who actually have a secondary screening at the clinic. Of these persons who are screened at the clinic, a number, k4, will have diastolic pressures below the second cut-off point, leaving N5 = N4 - k4, individuals with diastolic blood pressure greater than or equal to 90 mm. Hg who are eligible for treatment in the clinic. A number of these persons, k5, Vol. 52, No. 6, July-August 1976
654
S. WASSERTHEIL-SMOLLER AND M. D. BLAUFOX
will drop out at this stage, leaving N6 = N5 - k5 persons for whom treatment will be instituted at the facility. How can such information be used? One should look at this data from the end result when formulating criteria for elevated blood pressures: in order for a facility to treat No people who had fifth-phase diastolic blood pressure at 90 mm. Hg or above at the second screening, it would be necessary to initially enumerate and screen N1 people. If treatment facilities were available for twice the number of people, i.e., 2 x N6, it would be necessary to begin by trying to initially enumerate and screen 2 x N1 persons. The actual numbers for k1, k2, k3, k4, k5, and the corresponding percentages vary according to the race, sex, and age composition of the target population. For example, in the HDFP population approximately 78% of the individuals with diastolic pressures greater than or equal to 95 mm. Hg at the home screening agreed to come to the clinics for a secondary screen; that corresponds to N4. In general, blacks are less likely than whites to have a home screening or to come to the secondary clinic screening if they are found to be hypertensive at home screen, but are more likely than whites to have elevated blood pressures at the home screening. Surprisingly, men in both racial groups are more likely to come for the secondary clinic screening than women. The prevalence figures for the different groups are available in a variety of publications56 and shortly will be available from the HDFP broken down by age, sex, and race for a national group. Preliminary data from the HDFP,1 shown in Figure 2, indicates that at the home screening approximately 26% of black males, 21% of black females, 13% of white males, and 8% of white females had diastolic blood pressures greater than or equal to 95 mm. Hg. The prevalence of elevated diastolic blood pressure at the initial screen peaked at ages 50 to 54 in all sex-race groups. By considering these factors in the light of what treatment and follow-up facilities are available and how many patients can be handled, it is possible to determine how large a population should be screened in order to be able to take care of the hypertensive patients who will be identified. With regard to costs, in the saturation screening program in Co-Op City there were two kinds of screening situations. First, new households were assigned to an interviewer who tried to enumerate and screen the people in that household. If the occupants were not at home, the interviewer went on Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
655
to the next household on the list of assignments. Second, in an effort to screen the entire community, we also had a "clean-up period"; during this time the interviewers were assigned to households whose occupants initially had refused or with whom the interviewers initially had been unable to make contact. Obviously, some individuals are difficult to reach and more time is spent in case finding for this group. We estimated the costs of case finding in the two groups and found that 27% more money and time was spent on the refusals and no contacts than on new households. In any screening program it is desirable to consider to what extent efforts and funds should be deployed to recruit hard-to-reach persons. Finally, the screening effort of the national HDFP found that among the people of both races who had elevated blood pressure about 60% of the men and 80% of the women knew they had hypertension.1 However, a substantial number of people were newly identified as suspect hypertensives at the home screening. Black men probably are the group at highest risk. This group includes not only the greatest proportion of known hypertensives who are not under control, but also the largest proportion of new cases to be picked up at screening. It must be concluded that screening efforts cannot stand alone. The problem is not only how to identify and improve the follow-up and treatment of previously identified hypertensives, but how to provide facilities and care for the newly identified hypertensives as well. The criteria set forth in this discussion may serve as a guide to designing a screening effort which can be adjusted to the treatment resources which are available in the
community.
The clinical centers and investigative staffs of the Hypertension Detection and Follow-Up Program are: Atlanta, Ga.: Elbert Tuttle, M.D., Neil Shulman, M.D., Steven Heymsfield, M. D. Baltimore, Md.: George Entwisle, M.D., Aristide Apostolides, M.D. Birmingham, Ala.: Harold Schnaper, M.D., Albert Oberman, M.D. Boston, Mass.: Edward H. Kass, M. D., Ph. D., James 0. Taylor, M.D., B. Frank Polk, M.D. Chicago, Ill.: Jeremiah Stamler, M.D., Rose Stamler, M.A., Flora C. Gosch, M.D. Vol. 52, No. 6, July-August 1976
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Davis, Calif.: Nemat 0. Borhani, M.D., Dean T. Mason, M.D., Jess F. Kraus, Ph.D. East Lansing, Mich.: Sandra A. Daugherty, M.D., Ph.D., Robert M. Daugherty, Jr., M.D., Ph.D. Evans County, Ga.: Curtis G. Hames, M.D., Iqbal Krishan, M.D. Georgetown, Washington, D.C.: Frank A. Finnerty, M.D. Jackson, Miss.: Herbert G. Langford, M.D., Myra Tyler, M.D., R. L. Watson, D.V.M., Ph.D. Los Angeles, Calif.: Morton H. Maxwell, M.D., Roger Detels, M.D., Paul Varady, Ph.D., Andrew Lewin, M.D., Marilyn Farber, M.P.H., Joan Ignatius, R.N. Minneapolis, Minn.: Reuben Berman, M.D., Ronald J. Prineas, M.B., B.S., Ph.D., K. Wang, M.D. New York, N. Y.: M. Donald Blaufox, M.D., Ph.D., Sylvia Wassertheil-Smoller, Ph.D. Salt Lake City, Utah: C. Hilmon Castle, M.D., Irving Urshler, M.D. REFERENCES 1. Oberman, A.: Results of two stage screen in the Hypertension Detection and Follow-up Program (HDFP) on behalf of the national collaborative group HDFP. Circulation (Suppl.) 50: 101, 1974. 2. Remington, R. D. and Richard, D.: The Hypertension Detection and Follow-Up Program (U.S.A.). Inst. Nat. Sante Rech. 21:185-94, 1973. 3. Abby, L. M.: Screening for hypertension in the dental office. Amer. Dent. Ass. 88:563-67, 1974. 4. Hammel, M. I. and Kabot, H. F.: Blood pressure screening in the community pharmacy. Amer. Pharm. Assoc. 14:196-97, 1974. 5. Schoenberger, J. A., Stamler, J., Shekelle, R. B., and Shekelle, S.: Current status of hypertension control in an industrial population. J. A.M.A. 222:559-62, 1972. 6. Wilber, J. A. and Barrow, J. G.: Hypertension: A community prob-
lem. Amer. J. Med. 52:653, 1972. 7. Mroczek, W. J., Martin, M., and Finnerty, F. A., Jr.: Detection of hypertension-Blood pressure determination in outpatient clinics of medical school-affiliated training programs. J.A.M.A. 231:126-66, 1975. 8. Inter-Society Commission for Heart Disease Resources: Guidelines for the detection, diagnosis and management of hypertensive population. Circulation 44: A263-72, 197 1. 9. Grant, J.: Quantitative evaluation of a screening program. Amer. J. Public Health 64:66-71, 1974. 10. Varady, P. D. and Maxwell, M. H.: Assessment of statistically significant changes in diastolic blood pressures. J.A.M.A. 221:365-68, 1972. 11. HDFP Collaborative Group: Improvement in current community control of hypertension. Circulation (Suppl.) 51-52:208, 1975.
Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES FOR A COMMUNITY HYPERTENSION-CONTROL PROGRAM* SYLVIA WASSERTHEIL-SMOLLER, Ph.D. Associate Professor, Department of Community Health
M. DONALD BLAUFOX, M.D., Ph.D. Associate Professor of Medicine and Radiology Albert Einstein College of Medicine Bronx, N.Y.
R
ECENT data 1,2,7 indicate that among those persons who had at one time been informed by their doctor that they had high blood pressure, only about half of the blacks and a little more than one third of the whites now are receiving appropriate therapy. Younger individuals in all of the race and sex groups are less likely to be receiving treatment for their hypertension, and if they are under treatment are less likely to be treated adequately. The importance of identifying and following the younger individuals is especially clear in view of these facts and in view of the prolonged impact that hypertension will have in the younger group. When we discuss the planning of case-finding activities, we must at the same time plan facilities for follow-up or treatment. Case finding without adequate planning for long-term treatment not only fails to reduce the impact of hypertension in the community, but also creates unrelieved anxiety in newly discovered patients. Thus, to be successful, case finding must be approached by working backward from a knowledge of the available capacity for follow-up treatment. For systematic planning of case finding it is necessary to have certain essential information so that we may calculate how many persons may be screened in order to yield a number of hypertensive patients that will neither overburden the available treatment and follow-up facilities nor underutilize them. *Presented in a panel, Case Finding, as part of a Conference on Developing and Managing Community Programs for the Control of Hypertension held by the New York Metropolitan Regional Medical Program at the New York Academy of Medicine April 15, 1975. This research was supported in part by Contract No. 1 HV22931 from the National Heart and Lung Institute, Bethesda, Md.
Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
649
The expected yield for treatment will depend on such factors as the following: 1) The definition of hypertension 2) The demographic composition of the target population 3) The prevalence rate for a population with that composition 4) The number of patients lost at different stages of the case-finding and follow-up procedures The first decision to be made is where and how the screening will take place. One may decide to do saturation screening. In that case, a target population such as a census tract, a housing development, or an industrial population would be selected, and an attempt would be made to screen everyone in it. The yield and loss to follow-up in such an undertaking may be quite different from that obtained in casual or opportunistic screening. In casual or opportunistic screening a station may be set up at a convenient location at which screening for hypertension would be made available to those who volunteer to have their pressures measured. It may be a single "one-shot" attempt, e.g., as at supermarkets, banks, or street corners on a specific day. Or casual screening may be conducted as a continued effort in a fixed location, e.g., a pharmacy or dentist's office.3 Proponents of screening for high blood pressure in pharmacies4 base their approach on the fact that in economically depressed areas the pharmacist is usually the last to move from the area and that people often look to the pharmacist as a source of medical care, making such a setting appropriate for screening. The problem with most of these programs is that a person's blood pressure is measured at the screening site and then there is little or no follow-up. The individual may be told that he or she has elevated blood pressure and should see a physician, but usually no attempt is made to determine whether, in fact, the patient did see a physician and whether his blood pressure has been brought under control. In fact, there is much evidence that diagnosed hypertensives are not treated adequately.5'6 More than half the patients with elevated blood pressure had previous knowledge of this and yet continued to have elevated pressures.7 Black individuals are less likely to have their hypertension under control than whites, men less likely than women. Further, persons who come voluntarily for screening tend to be older. Since the younger hypertensives may be at longer risk and may derive greater long-term benefits from therapy, they constitute an important group that may be missed through casual screening. This kind of Vol. 52, No. 6, July-August 1976
S. WASSERTHEIL-SMOLLER AND M. D. BLAUFOX
650
DIAGNOSIS
Screeninig results
Positive Netative Total
Sensitivity
Over-referral
Diseased a c
Nondiseased b d
Total a+b c 4d
a+c
b+d
a+b+c+d
a
Specitfcity
b b+d
a+,c 2 a+b
Under-referral
c c +d
screening, however, may be more economical and more practical in an individual situation. After choosing the appropriate screening method, the next major decision that has to be made is what blood-pressure point to use for the diagnosis of suspect hypertension. A variety of cut-off points have been used; it is important to have a precise, consistent definition. Some programs employ a systolic pressure of 140 mm. Hg or more or a diastolic pressure of 90 mm. Hg or more or both as diagnostic criteria and other programs use a systolic pressure of 160 mm. Hg or a diastolic of 95 mm. Hg or more or both.8 How does one decide which criteria to use for the diagnosis of hypertension in a screening program? It is desirable to have a screening test that is as specific as possible. The accompanying table illustrates the concepts of specificity, sensitivity, and over-referral and under-referral,9' which are utilized in this decision-making process. Specificity is the proportion of persons without the disease for whom the screening test is negative. It is determined by dividing the number of people who were screened as negative who did not have the disease by the total number of people who did not have the disease who were screened. Sensitivity is the proportion of persons with the disease for whom the screening test is positive. It is determined by dividing the number of people who were screened as positive who had the disease by the total number of people who had the disease who were screened. Over-referral is the proportion of people with positive screening results who are not diseased. It is determined by dividing the number of people who were screened as positive but did not have the disease by the total number of people who were screened as positive. Under-referral is the proportion of Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
651
people with negative screening results who had the disease. It is determined by dividing the number of people who were screened as negative but had the disease by the total number of people who were screened as negative. If the over-referral figure is large, facilities would be taxed unnecessarily, since many of the people who were judged positive in the first screening are not likely to be positive in the second screening. It would be better if the specificity were as high as possible. The ideal test would be negative for all well persons. One way to approach this goal is to have a two-stage screen with a higher cutoff point for the first screen than for the second. This was the decision reached in a major national program for hypertension detection and follow-up which shall be described briefly; it can serve as an example of how to use data effectively to plan case-finding efforts. The Hypertension Detection and Follow-Up Program (HDFP)2 is a 17-center national study to evaluate the efficacy of a community hypertension program. The Albert Einstein College of Medicine is a participant in the HDFP, with a center at Co-Op City, a middle-income housing development in the Bronx. The national program has screened 157,000 people between the ages of 30 and 69 years. This represents the largest screening effort for hypertension ever conducted in the United States, and the data on prevalence from this effort (to be published shortly) are the most recent figures available on the extent of this disease. At the New York Center in Co-Op City approximately 15,000 persons have been screened. In this program, saturation screening was employed at the Co-op City center. A target area was picked, each household within that area was enumerated to list all resident individuals, and a vigorous attempt was made to screen at home all age-eligible individuals, i.e., those 30 to 69 years of age. This program uses a two-stage screening based on -measurement of diastolic blood pressure alone. If an individual had a diastolic blood pressure of 95 mm. Hg or above at the home screening, he was asked to come to a specially established clinic for confirmation. If his diastolic blood pressure was 90 mm. Hg or above at the clinic screen, he was invited to become a participant in the program. There is a great variability in blood pressure. IO Among the people in the HDFP who were in the 95 to 104 mm. Hg stratum of blood pressure at home, 65% had less than 95 mm. Hg at the confirmation visit to the clinic; Vol. 52, No. 6, July-August 1976
652
S. WASSERTHEIL-SMOLLER AND M. D. BLAUFOX
90-104
105-114
115+
PESSUE Fig. 1. Estimated patient flow for two-stage screen. DEP -= diastolic blood pressure. DBP
-
DIASTOLIC BLOOD
45% had less than 90 mm. Hg at that repeat examination. Even among the people who had diastolic pressures of 115 mm. Hg or more at home, a full 10% had less than 90 mm. Hg at the clinic; only about one third of those with diastolic pressure greater than or equal to 115 mm. Hg at home showed this high level at the clinic.1 However, through specified cut-off Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
653
4.J
26%
be
QE E
0
+C00L *
21%
Al 13% 00
4-Jcu 0
~~~~~~~~~~~~~8%
4-i
WHBAK
Female Male BLACK
Fig. 2. Prevalence of elevated
(G
HT
Male Female WHITE
95 mm. Hg) diastolic blood pressure by race and sex.
points and the saturation method of screening, one can expect certain yields throughout the various screening stages, as illustrated in Figure 1, which is based on HDFP data. If one starts with a group of age-eligible individuals, N1, a certain number of these individuals, k1, will refuse to be screened at home. This will result in a group of persons, N2, who participate in a home screening (N2 is the N1 eligibles minus the k1 persons refusing home screening). Of those who are screened at home, a number of these individuals, k2, will have diastolic pressure less than 95 mm. Hg, leaving N3 = N2- k2 individuals eligible for a second screening at the clinic. Of these persons, a certain number, k3, will not show up at the clinic, leaving N4 = N3- k3 individuals who actually have a secondary screening at the clinic. Of these persons who are screened at the clinic, a number, k4, will have diastolic pressures below the second cut-off point, leaving N5 = N4 - k4, individuals with diastolic blood pressure greater than or equal to 90 mm. Hg who are eligible for treatment in the clinic. A number of these persons, k5, Vol. 52, No. 6, July-August 1976
654
S. WASSERTHEIL-SMOLLER AND M. D. BLAUFOX
will drop out at this stage, leaving N6 = N5 - k5 persons for whom treatment will be instituted at the facility. How can such information be used? One should look at this data from the end result when formulating criteria for elevated blood pressures: in order for a facility to treat No people who had fifth-phase diastolic blood pressure at 90 mm. Hg or above at the second screening, it would be necessary to initially enumerate and screen N1 people. If treatment facilities were available for twice the number of people, i.e., 2 x N6, it would be necessary to begin by trying to initially enumerate and screen 2 x N1 persons. The actual numbers for k1, k2, k3, k4, k5, and the corresponding percentages vary according to the race, sex, and age composition of the target population. For example, in the HDFP population approximately 78% of the individuals with diastolic pressures greater than or equal to 95 mm. Hg at the home screening agreed to come to the clinics for a secondary screen; that corresponds to N4. In general, blacks are less likely than whites to have a home screening or to come to the secondary clinic screening if they are found to be hypertensive at home screen, but are more likely than whites to have elevated blood pressures at the home screening. Surprisingly, men in both racial groups are more likely to come for the secondary clinic screening than women. The prevalence figures for the different groups are available in a variety of publications56 and shortly will be available from the HDFP broken down by age, sex, and race for a national group. Preliminary data from the HDFP,1 shown in Figure 2, indicates that at the home screening approximately 26% of black males, 21% of black females, 13% of white males, and 8% of white females had diastolic blood pressures greater than or equal to 95 mm. Hg. The prevalence of elevated diastolic blood pressure at the initial screen peaked at ages 50 to 54 in all sex-race groups. By considering these factors in the light of what treatment and follow-up facilities are available and how many patients can be handled, it is possible to determine how large a population should be screened in order to be able to take care of the hypertensive patients who will be identified. With regard to costs, in the saturation screening program in Co-Op City there were two kinds of screening situations. First, new households were assigned to an interviewer who tried to enumerate and screen the people in that household. If the occupants were not at home, the interviewer went on Bull. N. Y. Acad. Med.
PLANNING CASE-FINDING ACTIVITIES
655
to the next household on the list of assignments. Second, in an effort to screen the entire community, we also had a "clean-up period"; during this time the interviewers were assigned to households whose occupants initially had refused or with whom the interviewers initially had been unable to make contact. Obviously, some individuals are difficult to reach and more time is spent in case finding for this group. We estimated the costs of case finding in the two groups and found that 27% more money and time was spent on the refusals and no contacts than on new households. In any screening program it is desirable to consider to what extent efforts and funds should be deployed to recruit hard-to-reach persons. Finally, the screening effort of the national HDFP found that among the people of both races who had elevated blood pressure about 60% of the men and 80% of the women knew they had hypertension.1 However, a substantial number of people were newly identified as suspect hypertensives at the home screening. Black men probably are the group at highest risk. This group includes not only the greatest proportion of known hypertensives who are not under control, but also the largest proportion of new cases to be picked up at screening. It must be concluded that screening efforts cannot stand alone. The problem is not only how to identify and improve the follow-up and treatment of previously identified hypertensives, but how to provide facilities and care for the newly identified hypertensives as well. The criteria set forth in this discussion may serve as a guide to designing a screening effort which can be adjusted to the treatment resources which are available in the
community.
The clinical centers and investigative staffs of the Hypertension Detection and Follow-Up Program are: Atlanta, Ga.: Elbert Tuttle, M.D., Neil Shulman, M.D., Steven Heymsfield, M. D. Baltimore, Md.: George Entwisle, M.D., Aristide Apostolides, M.D. Birmingham, Ala.: Harold Schnaper, M.D., Albert Oberman, M.D. Boston, Mass.: Edward H. Kass, M. D., Ph. D., James 0. Taylor, M.D., B. Frank Polk, M.D. Chicago, Ill.: Jeremiah Stamler, M.D., Rose Stamler, M.A., Flora C. Gosch, M.D. Vol. 52, No. 6, July-August 1976
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Davis, Calif.: Nemat 0. Borhani, M.D., Dean T. Mason, M.D., Jess F. Kraus, Ph.D. East Lansing, Mich.: Sandra A. Daugherty, M.D., Ph.D., Robert M. Daugherty, Jr., M.D., Ph.D. Evans County, Ga.: Curtis G. Hames, M.D., Iqbal Krishan, M.D. Georgetown, Washington, D.C.: Frank A. Finnerty, M.D. Jackson, Miss.: Herbert G. Langford, M.D., Myra Tyler, M.D., R. L. Watson, D.V.M., Ph.D. Los Angeles, Calif.: Morton H. Maxwell, M.D., Roger Detels, M.D., Paul Varady, Ph.D., Andrew Lewin, M.D., Marilyn Farber, M.P.H., Joan Ignatius, R.N. Minneapolis, Minn.: Reuben Berman, M.D., Ronald J. Prineas, M.B., B.S., Ph.D., K. Wang, M.D. New York, N. Y.: M. Donald Blaufox, M.D., Ph.D., Sylvia Wassertheil-Smoller, Ph.D. Salt Lake City, Utah: C. Hilmon Castle, M.D., Irving Urshler, M.D. REFERENCES 1. Oberman, A.: Results of two stage screen in the Hypertension Detection and Follow-up Program (HDFP) on behalf of the national collaborative group HDFP. Circulation (Suppl.) 50: 101, 1974. 2. Remington, R. D. and Richard, D.: The Hypertension Detection and Follow-Up Program (U.S.A.). Inst. Nat. Sante Rech. 21:185-94, 1973. 3. Abby, L. M.: Screening for hypertension in the dental office. Amer. Dent. Ass. 88:563-67, 1974. 4. Hammel, M. I. and Kabot, H. F.: Blood pressure screening in the community pharmacy. Amer. Pharm. Assoc. 14:196-97, 1974. 5. Schoenberger, J. A., Stamler, J., Shekelle, R. B., and Shekelle, S.: Current status of hypertension control in an industrial population. J. A.M.A. 222:559-62, 1972. 6. Wilber, J. A. and Barrow, J. G.: Hypertension: A community prob-
lem. Amer. J. Med. 52:653, 1972. 7. Mroczek, W. J., Martin, M., and Finnerty, F. A., Jr.: Detection of hypertension-Blood pressure determination in outpatient clinics of medical school-affiliated training programs. J.A.M.A. 231:126-66, 1975. 8. Inter-Society Commission for Heart Disease Resources: Guidelines for the detection, diagnosis and management of hypertensive population. Circulation 44: A263-72, 197 1. 9. Grant, J.: Quantitative evaluation of a screening program. Amer. J. Public Health 64:66-71, 1974. 10. Varady, P. D. and Maxwell, M. H.: Assessment of statistically significant changes in diastolic blood pressures. J.A.M.A. 221:365-68, 1972. 11. HDFP Collaborative Group: Improvement in current community control of hypertension. Circulation (Suppl.) 51-52:208, 1975.
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