How physicians use laboratory tests.

The aim of our study was to measure the ways in which a physician perceives and reacts to a laboratory result. After reviewing a series of brief clinical problems, physicians were asked to indicate the change in test results that would alter the diagnosis or treatment. Although there were wide differences in attitudes, the pattern of responses from 125 internists offered estimates of what is a clinically important change. In selected clinical settings, the change in successive measurements chosen with the greatest frequency as indicators of a clinically important change in level were glucose, 35 mg/dl; BUN, 6 mg/dl; serum sodium, 4 to 6 mEq/liter; serum potassium, 4 to 6 mEq/liter; uric acid, 8 mg/dl; creatinine, 0.4 mg/dl; serum calcium, 4 to 5 mg/dl; triglycerides, 20 mg/dl; hemoglobin, 1 g/dl; and serum osmolality, 11 mOsm/kg. The responses were compared with estimates of laboratory precision drawn from a national quality control program. The quality of laboratory testing was rated as satisfactory for clinical use in four of five clinical settings. The study points out the need to correlate the activities in the clinical laboratory with the application of test results in the care of patients.