Diagnostic accuracy of blood and CSF lactate in identifying children with mitochondrial diseases affecting the central nervous system

Objective: To determine the diagnostic accuracy of blood and cerebrospinal fluid (CSF) lactate and pyruvate concentrations in identifying children with mitochondrial diseases (MD) affecting the central nervous system (CNS). Methods: We studied lactate and pyruvate concentrations in paired samples of blood and CSF collected concurrently from 17 patients with MD (Leigh encephalomyelopathy 10, MELAS 5, Pearson disease 1, PDH deficiency 1) and those from control patients (n = 49). Results: Although blood and CSF variables (lactate, pyruvate concentrations and lactate/pyruvate ratio) were significantly higher in the mitochondrial group than in the control group, there was considerable overlap of individual values between these two groups. The maximum value of the area under the receiver operating characteristic curve (AUC) was observed for the CSF lactate concentration (0.994, optimal cut-off value 19.9 mg/dl, sensitivity 0.941 and specificity 1.00), followed by the CSF pyruvate level (0.983). There was an inverse relationship between blood lactate and lactate CSF/blood ratio. For blood lactate concentrations between 20 and 40 mg/dl, a significant difference was also noted in the lactate CSF/blood ratio between the two groups (AUC 1.0, optimal cut-off value 0.91, sensitivity 1.0 and specificity 1.0). Conclusions: Our study suggests that that CSF lactate level > 19.9 mg/dl is the most reliable variable for identifying patients with MD affecting the CNS. When blood lactate concentrations are marginally elevated (20–40 mg/dl), lactate CSF/blood ratio > 0.91 may also provide diagnostic information.