Lactate-stress testing in 54 patients with mitochondriopathy.

Since there are only few data available about the lactate stress test in a group of patients with mitochondrial myopathy, we investigated the sensitivity of this test in a larger cohort of such patients. Serum lactate was determined before, during and after a 15 minute, constant 30 W workload on a bicycle ergometer in 47 controls, aged 15 to 72 years and 54 patients with mitochondrial myopathy, aged 15 to 74 years. Lactate's upper reference limits at rest, 5, 10, 15 minutes after starting, and 15 minutes after finishing the exercise were 2.0, 2.1, 2.1, 2.1 and 1.8 mmol/l respectively. The sensitivity of the lactate-stress test was 69%. The lactate-stress test complements electrophysiological and bioptical findings and proved to be helpful in diagnosing mitochondrial myopathy.