Plasma Lactate Response to a 12‐Min Walk Test Is a Poor Diagnostic Biomarker for Mitochondrial Myopathy

ABSTRACT Mitochondrial myopathy (MM) represents a group with a broad phenotypic spectrum which complicates the diagnostic process. This study investigated whether plasma lactate changes following a 12‐min walk test (12MWT) and 20‐min recovery could be a diagnostic screening tool for MM. Thirty patients with MM and 19 healthy controls (HC) participated. Total walking distance and heart rate during the test were measured, along with plasma lactate at rest, after exercise, and during recovery. For the latter, we calculated the area under the curve (AUC). The results were compared between groups. MM patients walked shorter (1082 m [994–1143] m vs. 1349 m [1149–1435], p = 0.0005) and had higher resting lactate (1.7 ± 1.2 mmol/L vs. 0.9 ± 0.3 mmol/L, p = 0.003). No significant difference in plasma lactate was observed after exercise. Plasma lactate AUC during recovery was similar between groups. Thus, the 12MWT is not a reliable screening tool for MM as changes in plasma lactate during exercise and recovery did not differentiate MM from HC.