Iron deficiency anemia in the elderly: the diagnostic process.

OBJECTIVE: To determine the effectiveness of physician probability estimates calculated on the basis of findings from history-taking and physical examination in the diagnosis of iron deficiency anemia in elderly patients. DESIGN: Prospective study. SETTING: Two community hospitals offering secondary and tertiary care. PATIENTS: A total of 259 patients over 65 years of age found to have previously undiagnosed anemia. MEASURES: Physician estimates of the likelihood of iron deficiency before (pretest probability) and after (post-test probability) the laboratory test results were available. The hemogram was available to the physicians when they made their pretest probability estimates. Because the serum ferritin level proved to be the most powerful of the laboratory test results studied, the likelihood ratios associated with the post-test estimates were compared with the ratios associated with the serum ferritin level. MAIN RESULTS: The post-test probability estimates were influenced by the serum ferritin level and the pretest estimates. The post-test estimates derived from the findings obtained through history-taking and physical examination and the laboratory test results (including the serum ferritin level) were slightly less accurate in predicting iron deficiency than the serum ferritin level alone. Nevertheless, a model in which the pretest estimates were used in addition to the serum ferritin level to predict iron deficiency proved to be more powerful than the serum ferritin level alone (p = 0.006). This indicated that the limitations of the post-test estimates were due to a misinterpretation of the serum ferritin level and that the findings from history-taking and physical examination added important diagnostic information. CONCLUSIONS: Physicians must be aware of test properties to provide optimal care to their patients. If test results are properly interpreted, pretest probabilities derived from findings obtained through history-taking and physical examination can add useful information that will lead to more accurate diagnoses.