The accuracy of tuberculin skin tests: self-assessment by adult outpatients.

Tuberculin skin testing is an accurate, inexpensive screening procedure for detecting tuberculosis infection. The return visit needed to interpret the reaction is inconvenient, costly, and may contribute to under-utilization of the test. Although some clinicians ask patients to read their own purified protein derivative (PPD) test results, patient accuracy and the degree of teaching needed to learn this skill are unclear. This study evaluated the accuracy with which 145 outpatients read their own Mantoux skin test (PPD) reactions and reported by postcard after brief training by nurse practitioners. A total of 89 instructed patients returned postcards and also returned for clinician readings; 46 submitted postcards without returning; 7 returned but did not complete postcards; and 3 neither returned postcards nor returned for readings. Ten of 135 postcards were uninterpretable. For 81 subjects with both interpretable tuberculin self-assessment postcards and clinician readings, overall PPD classification agreement was 88 percent; Kappaw = +0.905 (P less than .001). Compared to clinician readings, 1 of 53 patients falsely reported a positive reaction (greater than or equal to 10 mm) and 2 of 25 patients falsely reported negative PPD readings (0-4 mm). There was 100 percent agreement between postcard readings and clinician classifications in a subgroup of patients (N = 26), prospectively identified by nurse practitioners as capable of accurate tuberculin self-assessment. Inter-clinician reading agreement (N = 37) was 89 percent; Kappaw = +0.943 (P less than .001). The brief standardized teaching protocol described can enable most patients to measure and report their PPD results. Study results suggest thatpostcard reports, especially negative ones, from a subgroup of patients selected for their skill in measuring their initial PPD wheal and ability to paraphrase instructions, might be substituted for clinician readings.

The effect of chest radiographs on the management and clinical course of patients with acute cough.

The authors studied 2018 consecutive patients with a cough of less than 1 month's duration, presenting for medical care with this problem for the first time. Chest films were taken of all of the last 1819 of these patients. After physicians had specified diagnoses and patient management plans for the last 1531 of these 1819 patients, 98 per cent of the 1531 were randomized either to a group whose chest films were then used in their care, or to a group whose chest films were not available to the physician. The results show that chest radiographs ordered by physicians resulted in potentially beneficial change in the care of only 3 per cent of patients. Only use of chest radiographs not ordered by physicians led to the appropriate addition of antibiotics to the care of patients with infiltrates, and probably to improved illness outcome. Criteria for efficient, effective use of chest radiographs in the management of patients with acute cough are needed.

Physicians' misunderstanding of normal findings.

Gorry, Pauker, and Schwartz [1] demonstrated that a normal test result, when assessed quantitatively, can sometimes be extremely valuable in differential diagnosis. In the present study we extend the principle of the normal finding to include signs and symptoms. This extension proved to be clinically valuable for the present population of patients with acute cough, because the identified normal findings provided significant (p less than 0.001) information predictive of radiographic pneumonia and unrelated to that provided by the abnormal findings. This suggests that both types of findings should be used to diagnose pneumonia efficiently. Another result of the extension of this principle to signs and symptoms was the identification of the clinicians' use (p less than 0.001) of abnormal findings but not (p greater than 0.75) normal findings when managing patients with acute cough. Several possible causes for this misuse of normal findings are discussed, including limitations in the clinicians' cognitive processing of "absent problems," emphasis on abnormal findings by patients, and confusing epidemiological terminology that discourages the recognition of pertinent normal findings.

Two studies of good clinical judgment.

There is a continuing controversy about the quality of unaided clinical judgment. This paper reports two studies that show that experienced medical providers made accurate probability assessments and applied those assessments to patient care in a manner consistent with principles of optimal decision making. In the first study, experienced clinicians and physician assistants accurately judged the relative frequency of three cough-related diagnoses in an outpatient population, suggesting that their encounter with several "unrelated" diagnostic problems does not interfere with their ability to judge accurately the frequency of any single diagnostic problem. In the second study, a group of clinicians assessed the probability that each patient seen in an outpatient clinic had pneumonia. Physicians were more likely to assign a pneumonia diagnosis and to order a radiograph for patients with a greater assessed probability of pneumonia (p less than 0.05). Most of the physicians appeared to use cutoff probabilities or "thresholds" above which they acted as though the patient had the disease and below which they acted as though the patient did not have the disease, consistent with rational decision-making principles. However, the threshold probabilities being used were quite different from physician to physician, implying that the physicians managed the patient population in a nonuniform manner. Thus it may be desirable to supplement "good" clinical judgment with decision aids to ensure standardized medical care.

Physician's use of probabilistic information in a real clinical setting.

This study reports on physicians' processing of probabilistic information while they were treating possible pneumonia patients at an outpatient clinic. Physicians overestimated the patients' probability of pneumonia but were sensitive to relative differences in the predictive value of symptoms when present and absent, and appeared to use base-rate information correctly when making clinical judgments.

Feedback and the illusion of validity in a medical clinic.

This paper discusses the effect of feedback from an imperfect diagnostic test-ordering decision upon clinicians' ability to evaluate their management strategies. It presents data from a medical outpatient clinic that show that physicians rely on chest radiographs to diagnose pneumonia but fail to request them for all patients with pneumonia. The data show that physicians preferentially use clinical attributes associated with pneumonia as perceived from the feedback of this imperfect chest radiograph-ordering decision (p less than 0.001) even though the attributes do not predict pneumonia as accurately as clinical attributes associated with all pneumonia cases (p less than 0.001). It is concluded that incomplete feedback based on an imperfect chest radiograph-ordering decision may perpetuate inefficient chest radiograph ordering patterns.