Background The identification of central nervous system (CNS) involvement by malignancies, using cytological analysis of CSF, is crucial for the appropriate treatment of patients.1 The aim of this study was to identify CSF specimen characteristics that have the highest diagnostic yield.

Methods We conducted a retrospective review of all CSF specimens submitted for cytological analysis at Cork University Hospital from January 2010 to December 2011.

Results 598 CSF samples were obtained from 390 people. The difference in volume between the diagnostic categories of equivocal (29%), inadequate (17%), positive (5%) and negative (48%) was found to be statistically significant, p-value <0.05 (kruskal-wallis test). Of the 66 (17%) requiring repeat CSF sampling 25% of initial samples were inadequate, falling to 10% on second sampling. The average volume of the initial samples was 2.72 ml, increasing to 3.93 ml on repeat sampling.

Discussion Conventional cytology has shown high specificity but low sensitivity, being positive in 45% to 94% of initial specimens.1 Our study shows that factors increasing the likelihood of a definite result include a sample volume greater than 3 ml, and repeating sampling.