Gene Xpert Mtb/Rif specificity and sensitivity in Tuberculosis diagnosis using urine samples from HIV patients with signs of Tuberculosis at the Moi teaching and referral hospital in western Kenya

Abstract

The Mycobacterium tuberculosis/Rifampin (Xpert MTB/RIF) has been reported to be a fast molecular tool in the determination of the existence of mycobacterium tuberculosis DNA in mucoid (sputum) samples. However, the deployment of Gene Xpert for testing non-sputum clinical samples in the diagnosis of suspected tuberculosis in western Kenya population has not been evaluated. We are reporting on Specificity and sensitivity of urine Gene Xpert MTB/RIF from HIV patients clinically suspected of tuberculosis. Urine analysis from 158 HIV patients suspected of TB with CD4+ count <200 cells/mm3 were done. Among the female 11% and 15% were positive based on urine Gene Xpert MTB/RIF and urine LAM respectively with a majority (71%) having CD4 >100 ˂200 cells/mm. Sensitivity and specificity of urine Xpert was equated to smear microscopy, at the same time with urine culture. Sensitivity of urine Xpert against sputum microscopy was 17%, with a positive predictive value of 29%. Specificity of urine Xpert against sputum microscopy was 91%, with a negative predictive value of 83%. Stratified by CD4 categories, the test showed to be more sensitive (30% vs 11%) and specific (92% vs 89%) in patients with CD4≤100˂200 cells/mm3 compared to those with CD4>100 ˂200 cells/mm3 respectively. The data suggest that Gene Xpert assay is a sensitive and specific tool that rapidly identifies Mycobacterium tuberculosis using urine as a sample in immunocompromised patients.