The effects of iatrogenic blood contamination on total nucleated cell counts and protein concentrations in canine cerebrospinal fluid

Background Cerebrospinal fluid (CSF) might be altered by iatrogenic blood contamination, precluding accurate diagnostic interpretation. Objectives Available formulas to correct for iatrogenic blood contamination are likely unreliable. Study objectives were to determine the effects of blood contamination on total nucleated cell counts (NCCs) and protein concentrations in canine CSF. Methods Two methods were followed to evaluate the effect of blood contamination on total NCC and protein concentrations in CSF. First, records from the Colorado State University Veterinary Teaching Hospital were retrospectively searched for dogs where CSF analysis was performed. Total NCCs, RBC counts, protein concentrations, and cytologic interpretations were recorded. Second, CSF from 4 canine patients and 3 research hounds was prospectively analyzed before and after known dilutions of whole blood were added. Results Of the 787 clinical samples analyzed, 108 samples had a cytologic diagnosis of blood contamination. RBC counts for all clinical samples ranged from 0 to 210,000 cells/μL. No correlation between total NCCs or protein concentrations with RBC counts were found when all samples were evaluated. Total NCCs and RBCs were weakly correlated in samples with a cytologic diagnosis of blood contamination and when ≥500 RBC/μL was present. When serial dilutions of whole blood were added to normal CSF, no significant changes were observed in the total NCCs of uncontaminated aliquots and contaminated aliquots containing up to 8480 RBC/μL. Conclusions Erythrocyte counts in blood‐contaminated canine CSF poorly correlate with total NCCs and protein concentrations. Using formulas to correct total NCCs and protein concentrations for the number of RBCs in CSF is inappropriate.