[Diagnosis in low prevalence of disease. Significance of specificity rather than sensitivity in sequencing of diagnostic tests]. / Diagnostik ved lave sygdomspraevalenser. Betydningen af specificitet fremfor sensitivitet for raekkefølgen af diagnostiske tests.

The significance of specificity rather than sensitivity for the sequence of diagnostic tests is discussed. The rule of thumb states that when the prevalence of disease is low it is advisable to save time and money by eliminating as many healthy individuals as possible from the test system.

A utility-based model for comparing the cost-effectiveness of diagnostic studies.

The effective cost of a diagnostic test is the money spent per unit of diagnostic performance. The latter can be measured as diagnostic utility (DU), the probability-weighted sum of the utilities of the four test outcomes TP, TN, FP, and FN: DU = U(TP)P(TP) + U(TN)P(TN) + U(FP)P(FP) + U(FN)P(FN). DU (which also is called expected utility) incorporates the clinical decision analytic variables sensitivity (Se), specificity (Sp), equivocal fraction (EF), disease probability (P(D)), and outcome utility (U). DU is not an inherent property of a diagnostic test but of test-observer interactions in a clinical setting. The model sets the effective cost (EC) of a diagnostic test = actual direct cost (ADC)/DU. When DU = 1 (perfect test) EC = ADC and the patient benefits from the test dollar for dollar. When DU less than 1, EC exceeds ADC. If DU approaches O, EC becomes infinite; the test has no effectiveness at any cost. DU depends strongly on P(D) if Se and Sp differ significantly; then EC also depends on P(D), and the effective cost of a test performed in the wrong P(D) setting may be several times its actual direct cost. This model of comparing effective costs compares actual direct cost with clinical measures of test performance and utility values that allow expression of patient/doctor fears and preferences. It offers a more clinically realistic setting than models based on costs alone.

Physicians as gatekeepers. The impact of financial incentives.

Incentives encouraging physicians to reduce their use of diagnostic tests are controversial. We studied physicians enrolled in an independent practitioner association who see both fee-for-service and prepaid (health maintenance organization [HMO]) patients concurrently. We asked the following questions: (1) Do physicians order fewer tests for their patients enrolled in an HMO relative to their patients seen on a fee-for-service basis? (2) Are any reductions in testing selective or indiscriminate? We reviewed the charts of 273 new patients, 167 enrolled in a fee-for-service system and 106 enrolled in an HMO, who were seen by 17 physicians "for a check-up," and graded test use as "indicated" or "discretionary." We used multiple logistic regression to control for the effects of patient age and sex. Patients in the HMO underwent fewer tests than did patients in the fee-for-service system, as well as fewer discretionary tests, but received the same proportion of preventive services. We conclude that physicians ordered fewer tests for patients in the HMO, apparently because of selective omission of discretionary tests. Physicians also did not reduce preventive services for patients in the HMO relative to all other physicians.

Medicare prospective payment and the use of medical technologies in hospitals.

Medicare's Prospective Payment System (PPS) created incentives to reduce the application of technology to hospitalized Medicare beneficiaries. Using data from 501 hospitals from 1980 and 1983-85, this study assesses changes in use of intensive care units and use of nonsurgical procedures before versus after implementation of PPS. The percent of hospitalized patients, both Medicare and non-Medicare, admitted to intensive care units increased post-PPS. Also, stays within such units remained constant. However, the percent of inpatients to whom several nonsurgical procedures were administered was lower post-PPS. For some (e.g., CAT scanning), the percentage of inpatients having the procedure continued to increase after PPS but at a much slower rate. For others, the percent of inpatients with the procedure declined at a faster rate (e.g., intravenous pyelogram). Still others showed utilization increases during 1980-83 followed by declines thereafter (e.g., occupational and physical therapy). Before 1983, there was almost no change in the number of routine tests per inpatient (e.g., serology and blood chemistry). Afterwards, there were major decreases. PPS has influenced the inhospital use of many nonsurgical procedures by both Medicare and non-Medicare patients.

Departments of medicine and international health.

There is an emerging role in international health for departments of medicine that care to accept the challenge. Supervised medical rotations in the developing world and the care of culturally distinct immigrant populations provide unique opportunities to expand the scope of medical education while emphasizing a sensitive and humanistic approach to health care. The restraints imposed by diminished laboratory support and limited availability of drugs can foster reliance on diagnostic skills and the essential elements of therapy. Medical schools may elect to become involved in international health, but they must do so without becoming exploitative. Rotations of students, residents, and faculty in both directions should lead to productive interaction at both the clinical and research levels, for all participants.

The influence of uninterpretability on the assessment of diagnostic tests.

A frequent problem faced by physicians utilizing diagnostic tests is the occurrence of uninterpretable test results. Such results, if they occur commonly, can seriously impair the diagnostic performance of the test. Moreover, in assessing the characteristics of the test, i.e. sensitivity, specificity, etc. failure to consider the impact of uninterpretability will artificially inflate the test characteristics. In this paper we explore the implications of this issue. We observe that a relevant factor is the potential repeatability of the test, i.e. whether the cause of uninterpretability is a transient phenomenon or an inherent property of the subject. We distinguish uninterpretable results, in which no result is obtained, from indeterminate results, in which the result is equivocal, or for which predisposing concomitant factors limit the interpretability of the result. Our results demonstrate that the naive approach of ignoring uninterpretable results in test assessments may indeed be unbiased in certain circumstances. However, if the cause of uninterpretability is related to disease status or to the potentially observable test result, then this approach will lead to bias. In either case, the frequency of uninterpretability is an important consideration in the cost-effectiveness of the test.

Teaching cost-effective diagnostic test use to medical students.

The purpose of this project was to develop and evaluate a program to teach medical students how to order diagnostic tests in a cost-effective manner. The 1-month educational program included a seminar, a simulated patient-care exercise, special case presentations by students, newsletters about diagnostic tests, and concurrent review of patients' bills. Content analysis of answers to open-ended questions and pretests and posttests were used to measure differences in the study and control groups. Although students said the program was useful, no significant differences were found in students' knowledge, attitudes, or simulated test-ordering behavior. The authors conclude that the lack of improvement in objective measures limits the potential effectiveness of restricted efforts such as this one and that the discrepancy between the subjective and objective measures reinforces the need for more rigorous evaluations of programs that teach cost-effective diagnostic test use.