Lactate stress testing in 155 patients with mitochondriopathy

Objective: Few data are available about the diagnostic yield of the lactate stress test (LST) in a large group of patients with mitochondriopathy (MCP). Methods: Serum lactate was determined once before, three times during, and once after a 15-minute, constant 30W workload on a bicycle in 62 controls, aged 17 to 84 years, 155 patients With MCP, aged 17 to 87 years, and 31 patients with neurological disorders other than MCP. Results: 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 test was regarded abnormal if more than two of the five lactate values exceeded the cut-off levels. Among the 103 patients with abnormal LST, 64 (62%) had normal resting lactate. The sensitivity of the test was 67% and the specificity 94%. Conclusion: The LST proved to have a high sensitivity and specificity in the detection of patients with MCP being thus a simple but powerful tool to assess the impaired oxidative metabolism in MCP patients.