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.