Serum lactate is frequently elevated at rest or during slight exercise in patients with mitochondriopathy (MCP). [1][2][3][4] The increase of serum lactate mainly results from defective respiratory chain enzymes in the skeletal muscles, leading to a reactive change from aerobic to anaerobic phosphorylation of adenosine diphosphate and an equilibrium shift of the pyruvate/lactate reaction towards lactate. [5][6][7][8] The increase of serum lactate during slight exercise is used for diagnostic purposes by means of the lactate stress test (LST). 3,[8][9][10][11][12][13][14] Despite increasing interest in this diagnostic tool and widespread application, little is known about the diagnostic yield of the LST in a large group of patients with MCP. This study was thus conducted, to assess the diagnostic yield of the LST in a large number of patients with MCP, diagnosed during five years. PATIENTS AND METHODSIncluded were all patients of the Neurological Hospital Rosenhügel, Vienna, in whom MCP was diagnosed between July ABSTRACT: 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.RÉSUMÉ: Test du lactate à l'effort chez 155 patients atteints de mitochondriopathie. Objectif: Il y a peu de données disponibles sur la valeur diagnostique du test du lactate à l'effort (TLE) chez un groupe important de patients atteints de mitochondriopathie (MCP). Méthodes: Le taux de lactate sérique a été déterminé avant, à trois reprises pendant et après un e activité physique de 15 minutes, d'intensité constante à 30W sur une bicyclette, chez 62 contrôles âgés de 17 à 84 ans, 155 patients atteints de MCP, âgés de 17 à 87 ans et 31 patients présentant d'autres pathologies neurologiques. Résultats: Le point de coupe supérieur des valeurs de référence au repos, 5, 10, 15 minutes après le début de l'exercice et 15 minutes après la fin de l'exercice étaient de 2,0, 2,1, 2,1, 2,1 et 1,8 mmol/L respectivement. Le test était considéré comme normal si plus de deux des cinq valeurs de lactate étaient supérieures au point de coupe. Parmi les 103 patients dont...

As it is under debate if determination of lactate during cycle ergometry (lactate stress testing, LST) under a continuous, unadjusted, low workload is a valuable diagnostic tool for mitochondrial myopathy (MMP), the present study aimed to investigate how sensitive the LST is in a large cohort of patients with indications for MMP (MMP patients). Serum lactate was determined once before, three times during, and once after a 15-min, constant 30 W-workload on a bicycle ergometer in 115 healthy controls, 166 patients with neurological disorders other than MMP, and 291 MMP patients. Serum lactate's upper reference limit at rest, 5, 10, 15 min after starting, and 15 min after finishing the exercise was 2.0, 2.0, 2.1, 2.0 and 1.7 mmol/l, respectively. Resting lactate was increased in 75 MMP patients (26%). The specificity of resting lactate determination was 84%. The sensitivity of the LST was 66% and the specificity 84%. Among the 192 MMP patients with abnormal LST, 120 (63%) had a normal resting lactate. The LST is abnormal in two thirds of the MMP patients. The sensitivity of the LST is higher than that of resting lactate determination. The LST is a simple and cheap but effective and reliable screening method for detecting the impaired oxidative metabolism in MMP.

Aim of the present study was to investigate the diagnostic yield of the lactate-stress-test in unselected patients with suspected respiratory-chain disorder (RCD). Serum lactate was determined before, during and after a 15-minute, constant 30W workload on a bicycle in 48 controls and 160 patients with suspected RCD. 122 had definite RCD, 38 neurological disorders other than RCD. The sensitivity, specificity, positive predictive value, negative predictive value and pre-test likelihood of the test was 69, 74, 89, 42 and 76% respectively. In conclusion, the lactate-stress-test proved a powerful tool to assess impaired oxidative metabolism in RCDs.

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Aim of the present study was to investigate the diagnostic yield of the lactate-stress-test in unselected patients with suspected respiratory-chain disorder (RCD). Serum lactate was determined before, during and after a 15-minute, constant 30W workload on a bicycle in 48 controls and 160 patients with suspected RCD. 122 had definite RCD, 38 neurological disorders other than RCD. The sensitivity, specificity, positive predictive value, negative predictive value and pre-test likelihood of the test was 69, 74, 89, 42 and 76% respectively. In conclusion, the lactate-stress-test proved a powerful tool to assess impaired oxidative metabolism in RCDs.