Validation of Mycobacterium tuberculosis real-time polymerase chain reaction for diagnosis of tuberculous meningitis using cerebrospinal fluid samples: a pilot study

Abstract

Background Timely diagnosis of tuberculous meningitis (TBM) remains challenging. Molecular diagnostic tools are necessary, particularly in low- and middle-income countries. There is no approved commercial polymerase chain reaction (PCR) assay that can be used to detect Mycobacterium tuberculosis in non-respiratory samples, such as the cerebrospinal fluid (CSF). We aimed to validate the threshold cycle (Ct) cut-off points; calculate the operational characteristics of real-time PCR for detection of M. tuberculosis (MTb qPCR) in the CSF; and the inhibitory affect of CSF red blood cells (RBC) and total proteins on MTb qPCR. Methods A total of 334 consecutive participants were enrolled. Based on clinical, laboratory and imaging data, cases of suspected TBM were categorized as definite, probable, possible or not TBM cases. Receiver operating characteristic curve analysis was used to select the best discriminating Ct value. Results For TBM cases categorized as definite or probable (n=21), the Ct validated for CSF (≤39.5) improved the diagnostic performance of MTb qPCR on CSF samples. The sensitivity was 29%, specificity was 95%, positive predictive value was 26%, negative predictive value was 95%, efficiency was 90% and positive likelihood was 5.3. The CSF RBC and total protein did not affect the positivity of the MTb qPCR. Conclusions These data support the validation of a highly specific but low sensitive MTb qPCR assay for the TBM diagnosis using CSF samples. MTb qPCR contributes significantly to the diagnosis, mainly when associated with conventional microbiology tests and clinical algorithms.

Diagnostic characteristics of Xpert MTB/RIF assay for the diagnosis of tuberculous meningitis and rifampicin resistance in Southern Brazil

“…The CSF samples of definite TBM are rare due to the difficulty to detect MTb in the CSF. In our study, the rate of CSF culture positivity for MTb was 29%; considering the groups with definite and probable TBM, this result was in accordance with that of the previous studies 27,39,40 . TBM accounts for 5% of all Tb cases; among which, 1.25% account for culture-proven TBM cases.…”

“…Traumatic CSF punctures are frequent in clinical practice, and the Xpert MTB/RIF was not validated for blood samples. However, a previous study with real-time PCR for the detection of M. tuberculosis (MTb qPCR) in the CSF showed that the number of RBC in the CSF did not inhibit the MTb qPCR 27 .…”

Central nervous system and spinal cord tuberculosis: Revisiting an important disease

“…Early and accurate diagnosis of CNS-TB challenging for several reasons as previously explained [12][13][14][15][16][17]. These factors led to the adoption of two main ways to approach a suspect patient for CNS-TB [21,22 and 74]:…”

“…However, these findings are nonspecific and may take time to settle. Apart from that, specific laboratory methods are often not available in the emergency setting [12].…”