The ischaemic lactate-ammonia test

The ischaemic lactate-ammonia test is widely used for investigating patients with muscle pain and fatigue. It involves measuring plasma lactate and ammonia produced as a result of forearm exercise under ischaemic conditions in a fasted subject. Its clinical use is to screen patients with muscle complaints for disorders of carbohydrate metabolism, in particular to identify those in whom further investigation may provide useful diagnostic information. There is a wide variety of methods described, reflecting attempts to optimize the response and hence the diagnostic value of the test. Although it is often considered a general screening test for metabolic muscle disease, the situations in which it is useful are specific. Here we review the use of the test and present the results of an audit of its use in our departments.