Objective.—To evaluate elevated patient calcium results as a postanalytic quality indicator of physician practices. Design.—Participants prospectively identified hypercalcemic patient results for 4 months or until they found 320 hypercalcemic results, and then, after at least 3 days, reviewed the medical records of these patients. Hypercalcemia was defined as a calcium value that exceeded the upper limit of each laboratory's reference range by 0.12 mmol/L or more. Participants, as well a subset of their physicians who did not acknowledge or respond to elevated results in the medical record, answered a questionnaire about their practices. Participants.—Five hundred twenty-five laboratories enrolled in the College of American Pathologists Q-Probes program. Main Outcome Measures.—The presence of hyercalcemic results in patients' medical records and physicians' acknowledgement and response to those elevated results. Results.—More than 5500 hypercalcemic results were identified, of which 53.2% represented a new finding. About 3.5% of results were not charted in the patients' records, and 23.1% of patient records did not contain clinician documentation of the abnormal result. Follow-up laboratory tests were not ordered for 13.8% of the elevated values. For 570 of the 808 results for which there was neither clinician documentation nor designated follow-up laboratory tests ordered, patients' physicians received written notification of the elevated calcium results along with a questionnaire. Responses were received from 386 physicians (68%). One hundred physicians indicated they did not order the specific calcium measurement, and of these 100, 85 responded it was part of a panel. The 286 physicians who ordered the test stated the results ultimately led to further testing (69%), a change of management (56%), or a new diagnosis (25%). Conclusions.—We found that a high percentage of abnormal results (3.5%) were not documented in the patients' medical records, the diagnosis of hypercalcemia frequently was new (53.2%), and a high percentage of physicians did not respond to elevated calcium results by writing a note (23.1%) or ordering another test (13.8%). Opportunities for quality improvement at these postanalytical steps are far greater than at the analytical step. Laboratorians must help physicians identify and respond to clinically important laboratory results.