Effects of time, initial composition, and stabilizing agents on the results of canine cerebrospinal fluid analysis

Background: Cerebrospinal fluid (CSF) is considered highly labile, but not all samples are analyzed immediately. Changes in the composition of CSF could potentially affect diagnostic test results and thus influence decisions about patient management. There has been little scientific inquiry into how variables such as time, initial composition, and storage conditions affect results of standard laboratory analysis of CSF. Objectives: The objectives of this study were to determine the effects of time, protein concentration, and presence or absence of exogenous stabilizing agents on standard CSF analysis results. Methods: Thirty abnormal CSF samples from 26 dogs were evaluated. Samples were divided into aliquots comprising different treatment groups and stored at 4 degrees C. Total nucleated cell count (TNCC), differential cell count (DCC), and cell morphology were evaluated for all groups; protein concentration was measured for selected groups. Unaltered aliquots were analyzed immediately (T-0Hr) and at 2,4, 8, 12, 24, and 48 hours (T-2Hr-T-48Hr); aliquots with added fetal calf serum (FCS) or hydroxyethyl starch (hetastarch) were analyzed at T-48Hr. Results: Significant time-dependent changes were observed in DCC in unaltered samples. Mononuclear cells deteriorated more rapidly than did neutrophils. Based on microscopic examination and subjective scoring of cell morphology, cells were consistently more degenerate by T-24Hr compared with T-0Hr, Samples with protein concentrations >= 50 mg/dL were less susceptible to cell deterioration than those with lower protein concentrations. Adding either FCS or hetastarch improved sample stability. Conclusions: Delayed analysis of canine CSF by 4-8 hours is unlikely to alter diagnostic interpretation, especially for samples with protein concentrations >= 50 mg/dL. The likelihood of misinterpretation is higher for samples with low cellularity or low protein concentration. We provide specific recommendations for adding FCS or hetastarch to samples that will not be analyzed within 1 hour.