Evidence for interference by ascorbate in the measurement of cerebrospinal fluid glucose by a kinetic glucose oxidase/peroxidase procedure.

Glucose in the cerebrospinal fluid (CSF) of neonates, as measured with a kinetic glucose oxidase/peroxidase procedure, was sometimes very low. When these samples were stored at 4 degrees C and subsequently re-analyzed, or if the samples were analyzed at any time after receipt by using a glucose dehydrogenase assay, the values were much higher. We found that the discrepancies in the values were caused by a lag phase in the kinetic method, during which no color developed. Because the lag phase exceeds the time over which the reaction is monitored in the kinetic procedure, this leads to the erroneously low values. The interference could be reproduced experimentally by adding ascorbic acid to CSF or plasma samples, or removed by adding ascorbate oxidase to CSF samples. Plasma glucose, as estimated by the kinetic glucose oxidase method, showed no such interference.