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Am Fam Physician. 1998;57(4):820

Although hospital protocols vary in regard to the work-up of suspected myocardial infarction, most include tests for creatine kinase (CK), with or without lactate dehydrogenase (LDH), to rule out myocardial infarction. With the introduction of CK isoenzyme MB (CK-MB) measurements, LDH isoenzyme testing has been shown to have a minimal role in excluding myocardial infarction in patients with chest pain of less than 24 hours' duration. Randall and Jones evaluated the institutional impact of eliminating LDH testing from their hospital's cardiac protocol and surveyed 100 U.S. hospitals to determine which tests are routinely performed to rule out myocardial infarction.

There was no report of harm to a patient during the 12 months after LDH testing was removed from the routine cardiac enzyme protocol. Of the 200 patients with one or more abnormal cardiac enzyme levels, none had positive LDH results and negative CK-MB results. No patients had a diagnosis of acute myocardial infarction on the basis of the LDH isoenzyme results.

In the year before elimination of LDH testing from the protocol, 6,177 LDH isoenzyme tests were ordered. The total annual cost was more than $47,000 at this hospital. In the intervention year, only 14 LDH isoenzyme tests were ordered, costing $154. All yielded negative results. Removal of LDH isoenzyme testing from the protocol cut the expenditure for this test by more than 99 percent.

Despite data showing little benefit of routine LDH isoenzyme testing and national consensus recommendations that this testing be abandoned, the authors' nationwide survey of 100 hospitals revealed that two thirds of the hospitals continue to use such testing in their cardiac protocols. Of the 66 hospitals that require routine LDH testing on the day of admission, 12 percent have it ordered every six to 12 hours, 55 percent every eight hours and 33 percent daily.

The authors conclude that routine LDH isoenzyme testing is unnecessary in patients who present within the first 24 hours of a possible acute myocardial infarction. Guidelines endorsed by organizations such as the American Heart Association recommend that levels of LDH and LDH isoenzymes be determined only in patients with negative results on CK tests and chest pain of more than 24 hours' duration. The authors also propose that elimination of LDH tests in this setting is likely to be well accepted and to yield substantial institutional savings.

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