Reasons for ordering laboratory tests and relationship with frequency of abnormal results.

AbstractObjective. Laboratory tests are ordered on a daily basis, even though disease probability is often very low. Abnormal results, especially mildly abnormal results, can be difficult to interpret in these circumstances. Further insights into the occurrence of abnormalities can help improve rational test ordering and test interpretation. The objective was therefore to examine the frequency of mildly and markedly abnormal results and their relationship with physicians' reasons for ordering tests. Design. Prospective study. Participants. A total of 87 primary care physicians in the Netherlands collected data on 1775 patients. Main outcome measures. The physicians recorded the reason for ordering the tests, the most probable diagnosis and the pretest probability. The laboratories' reference values and specified “action limits” were used to assess the number of abnormal results and markedly abnormal results, respectively. Results. Laboratory results were received for 1621 patients and 15,603 tests were re...