Reliable cerebrospinal fluid cytology reporting over an extended period: Is it possible by adding formol saline and ethylenediaminetetraacetic acid as cell preservative?

Background: Reporting cerebrospinal fluid (CSF) cytology within a narrow time frame is crucial as it is often indicated in critically ill patients and moreover, the cells in CSF are highly labile and tend to decline rapidly on standing. However, due to various logistic issues, delay in reporting is inevitable at times, especially if ancillary tools are required. In this study, we examine the effect of using formol saline and ethylenediaminetetraacetic acid (EDTA) as a preservative on the cellular composition of CSF at 18, 24, and 48 hours of preservation.

Methods: Thirty CSF specimens were examined within 2 hours of collection and this reading was recorded as time zero reading. The CSF specimens were then divided in three tubes with: (a) preservative:CSF ratio of 1:1; (b) preservative:CSF ratio of 1:5; and (c) no preservative. Total and differential leucocyte counts and immunocytochemistry were performed on the three specimens at 18, 24, and 48 hours and were compared with the readings at 0 hour.

Results: Preserved CSF (in the ratio of 1:5) showed no significant decrease in the number of cells at 18 hours (P = .4), 24 hours (P = .3), and 48 hours (P = .1). Cellularity decreased by 8.5%, 22%, and 40% at 18, 24, and 48 hours, respectively. Cell morphology and antigenicity were well preserved at all the three time intervals.

Conclusion: Formol saline and EDTA, when mixed with the CSF in the ratio of 1:5, can preserve significant cellularity for up to 24 hours.