Stability of cerebrospinal fluid/serum glucose ratio and cerebrospinal fluid lactate concentrations over 24 h: analysis of repeated measurements

Background: The cerebrospinal fluid/serum glucose ratio (CSF/S-glu) and CSF lactate measurements are part of the routine CSF work-up. The in-vitro stability of both metabolites in CSF has not been formally investigated. Methods: Following collection, CSF/S-glu and CSF L-lactate concentrations were measured repeatedly at five time points (baseline, 1 h, 2 h, 4 h and 24 h) in CSF and whole blood specimens stored at 4 degrees C. Results: CSF glucose and lactate concentrations were stable over 24 h in samples with both normal and increased CSF cell counts. The CSF cell count did not influence CSF glucose concentrations, but correlated significantly with CSF lactate concentrations. The CSF/S-glu increased significantly over time due to glucose consumption. Conclusions: Glucose and L-lactate are stable in CSF specimens at 4 degrees C over 24 h. The CSF/S-glu seems to be more reliable than CSF lactate because it is independent of the cell count. Falsely increased CSF/S-glu may be corrected by the rate of consumption of blood glucose. Clin Chem Lab Med 2010;48: 209-12.