Detection of Mycobacterium tuberculosis in urine by GeneXpert MTB/RIF as a useful diagnostic tool in urinary tuberculosis

Abstract

Background: Early and accurate diagnosis of urinary tuberculosis (UTB) is difficult as current diagnostic methods are lack of specificity (biochemical levels), lack of sensitivity (acid-fast bacilli stains), and time-consuming (TB culture). GeneXpert MTB/RIF has been endorsed by WHO and Indonesia Ministry of Health particularly for the sputum, and also gastric and lymph fluid samples. Given the limited data on the utility of GeneXpert MTB/RIF for urine samples, the recommendations do not apply to these samples. Case Description: A 38 y old woman was referred to the tertiary care hospital with suspected nephrolithiasis. She had a history of mild to moderate chronic flank pain and found to have left hydronephrosis on renal ultrasound. Ureteroscopy showed diffuse whitish necrosis of ureteral mucosa and ureteropelvic junction which was suspicious of tuberculous ureteritis. The acid-fast bacilli (AFB) smears gave negative result. Early morning sample was sent for GeneXpert MTB/RIF and the result was MTB detected with rifampin resistance not detected. The patient was managed with 6 m antituberculosis treatment according to the Ministry of Health regulation. Discussion: UTB was diagnosed using the urine AFB test, urine TB culture test and GeneXpert. Although the urine AFB test is simple, economical, and rapid, it has low sensitivity and specificity. TB culture has higher specificity compared AFB test but requires eight ws before the results are obtained. GeneXpert MTB/RIF, a real-time PCR, is a sensitive and specific test with 131 cfu/mL limit of detection that allows for early detection of TB. AFBs are intermittently shed in urine and the sensitivity of GeneXpert can be improved by using early morning urine for extended periods ranging from three to five days. Conclusion: GeneXpert MTB/RIF performed on urine samples is useful and can be recommended for rapid and reliable diagnosis of UTB in clinical practice esepecially in area with high TB burden. The diagnostic accuracy of urine GeneXpert MTB/RIF should be characterised further via prospective studies.