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

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.

Cerebrospinal fluid lactate as a predictive biomarker for tuberculous meningitis diagnosis.

OBJECTIVES: The definitive diagnosis of tuberculous meningitis (TBM) is achieved by identifying Mycobacterium tuberculosis (MTb) in cerebrospinal fluid (CSF); however, diagnostic confirmation is difficult due to the inability of current tests for an effective diagnosis. Our objective was to retrospectively assess the characteristics of CSF lactate (CSF-LA) as an adjunct biomarker in the diagnosis of TBM. METHODS: 608 CSF laboratory reports were assessed. Of these, 560 had clinically suspected TBM. These were classified as definite (n=36), probable (23), possible (278), or non-TBM (223) according to the international consensus TBM case definitions. An additional 48 CSF samples were negative controls with normal CSF. RESULTS: Against a reference standard of definite TBM, the cut-off value for CSF-LA was 4.0 mmol/L, the area under the ROC curve was 0.88 (95% CI, 0.82-0.94; p=0.0001), sensitivity was 69%, specificity 90%, negative predictive value 98%. These diagnostic parameters decreased when calculated against those of the other categories of TBM. CSF-LA exhibited high specificity, efficiency, negative predictive value, and clinical utility index in all the groups studied. CONCLUSIONS: CSF-LA is a useful diagnostic marker to rule out TBM when associated with conventional microbiology tests, nucleic acid amplification assays, and clinical algorithms, particularly in endemic areas.

Real-time Polymerase Chain Reaction for Mycobacterium tuberculosis Meningitis is More Sensitive in Patients with HIV Co-Infection.

BACKGROUND: Tuberculous meningitis (TbM) is the most severe complication of extra pulmonary tuberculosis (Tb). There is a higher frequency of positive cerebrospinal fluid (CSF) cultures for Mycobacterium tuberculosis (MTb) in samples from human immunodeficiency virus (HIV) co-infected patients than in those from HIV-negative patients. We hypothesized that real time PCR assays for MTb (MTb qPCR) using CSF would be more sensitive in HIV co-infected patients owing to a greater MTb burden. The present study aimed to verify the diagnostic performance of MTb qPCR in CSF of TbM patients who either were co-infected with HIV or were HIVnegative. METHODS: A total of 334 consecutive participants with suspected TbM were divided into two groups: HIV co-infected and HIV-negative; each group was categorized into definite TbM, probable TbM, possible TbM, and TbM-negative subgroups based on clinical, laboratory and imaging data. We evaluated the diagnostic characteristics of MTb qPCR analysis to detect TbM in CSF by comparing the results to those obtained for definite TbM (i.e., positive MTb culture) and/or probable TbM in CSF, as gold standard. RESULTS: The sensitivity of MTb qPCR in the definite and probable subgroups of the HIV coinfected participants (n = 14) was 35.7%, with a specificity of 93.8%, negative predictive value (NPV) of 94.4%, and negative clinical utility index (CUI-) of 0.89. Results of the HIV-negative group (n = 7) showed lower sensitivity (14.3%) and similar specificity, NPV, and CUI-. CONCLUSION: The findings confirmed our hypothesis, despite the low sensitivity. MTb qPCR may significantly contribute to diagnosis when associated with clinical criteria and complementary examinations.