Acid fast bacillus smear, mycobacterial culture and Xpert MTB/RIF assay for the diagnosis of tuberculous peritonitis in patients with and without end stage renal failure.

Introduction: Diagnosis of tuberculous peritonitis (TBP) requires a high index of suspicion. Hypothesis /gap statement: Information about the diagnostic features of TBP among patients with end-stage renal failure (ESRF) from India is limited. Aim: To assess the utility of the Gene Xpert MTB/RIF assay in the diagnosis of TBP in patients with end-stage renal failure (ESRF), compared with those without ESRF. Methodology: This prospective observational single centre cohort study was performed at a tertiary care centre in Northern India. Ascitic fluid and/or whole continuous ambulatory peritoneal dialysis (CAPD) bag with effluent from 300 clinically suspected cases of TBP were included in the study. Diagnosis was based on detection of Mycobacteria on smear, Xpert MTB/RIF assay and/or culture. Cell counting was done in a Neubauer chamber. Cell predominance was seen by Giemsa stain. Line probe assay (LPA) for drug susceptibility testing was performed on all positive cultures. Results: TBP was diagnosed in 168 cases. Diabetes mellitus was a significant risk factor for developing TBP in patients with ESRF (P value<0.01). Lymphocytic predominance was seen in 21 patients without ESRF (P value 0.033) while majority of the patients in both groups had neutrophils in their ascitic and peritoneal fluids (138/168; P value 0.033). We recovered 15 cases of laboratory diagnosed TBP (11 without ESRF and four with ESRF). Microscopy was positive in two cases while ten isolates were recovered on culture. The Xpert MTB/RIF assay was positive in seven ascitic fluid samples out of which three were rifampicin resistant. All these were patients without renal failure (P value 0.010). Eight culture positive samples tested by the line probe assay did not detect any resistance to either rifampicin or isoniazid. Conclusion: The GeneXpert MTB/RIF assay has a limited value in the diagnosis of TBP in patients with ESRF.