Cerebrospinal Fluid (CSF) cytology is thought to be the gold standard for diagnosing neoplastic meningitis. The accuracy of this test is important since it may determine whether or not a patient is given intra-thecal chemotherapy. Previous studies indicate that >10.5ml of CSF should to be collected in order to achieve a false negative rate of ≤3% and European Guidelines on CSF analysis recommend that this be the minimum volume collected.
275 consecutive CSF cytology samples from the West Midlands regional clinical neuroscience and haemo-oncology centre were audited to see how many met this standard.
The median volume of CSF sent for cytology was 2 ml (IQR1 to 5 ml). In fact only 2 (<1%) of the samples met the standard of >10.5 ml, though a further 22 (8%) of samples were close at 10 to 10.5 ml.
A re-evaluation is needed of the way in which neoplastic meningitis is diagnosed in the West Midlands. If newer techniques are sufficiently sensitive to allow an acceptable false positive rate with a lower volume of CSF, local guidelines should be drawn up which take this into account, otherwise the doctors collecting the samples need to be educated and monitored to ensure they meet the established standard.