How Low is Low Volume of Cerebrospinal Fluid from Suspected Cases of Tuberculous Meningitis to Refuse Acceptance in the TB Laboratory?

In tuberculous meningitis (TBM) the paucibacillary nature of the cerebrospinal fluid (CSF) and low sample volume pose a major challenge, especially in young children and low volume samples are often refused by the laboratory. To understand the significance of sample volume, all CSF samples from suspected cases of TBM were accepted. The diagnostic yield of various diagnostic tests was analysed considering various volume ranges. Of the total 571 samples studied, the overall detection rates of Ziehl-Neelsen (ZN) microscopy, culture on Löwenstein-Jensen (LJ) medium, MGIT-960 liquid culture and polymerase chain reaction (PCR) were 0.4%, 8.1%, 18.9% and 13.8%, respectively. Low sample volume did not alter the turnaround time for LJ and MGIT positivity, which was 5.94 ± 0.97 wk for LJ and 20.2 ± 6.4 d for MGIT culture. This study found that if the laboratory is equipped with facilities like MGIT-960 culture and any molecular tests, no amount of CSF should be refused by the laboratory.