Oral rifampicin interferes with urine dipstick tests for patients with pulmonary tuberculosis.

BACKGROUND: Rifampicin (RMP) and its major metabolite, desacetyl rifampicin (dRMP), can interfere with urine dipstick tests (UDTs) in patients with tuberculosis (TB) who receive oral RMP. This study sought to examine the effects of RMP and dRMP on UDTs using 2 different urine dipsticks (i.e., Arkray's Aution Sticks 10EA and GIMA's Combi-Screen 11SYS Plus sticks).

METHODS: Urine colorimetry was applied to measure RMP concentrations and determine the range of total RMP concentration in the urine within 2-6 and 12-24 h of oral administration of RMP. In vitro interference assays and confirmatory tests were performed to evaluate the effects of RMP and dRMP on the analytes.

RESULTS: The total RMP concentration in the urine of the 40 TB patients analyzed as urine sample was 88-376 µg/mL within 2-6 h and 22-112 µg/mL within 12-24 h of oral administration of RMP. Interference was observed for different analytes at consistent or varied RMP concentrations between the in vitro interference assays and the confirmatory tests, including 75 patients [Aution Sticks 10EA: 250, 250 µg/mL for protein (PRO); 400, 300 µg/mL for leukocyte esterase (LEU); Combi-Screen 11SYS Plus: 125, 150 µg/mL for ketones (KET); 500, 350 µg/mL for nitrite (NIT); 200, 300 µg/mL for PRO; 125, 150 µg/mL for LEU].

CONCLUSIONS: RMP and dRMP interfered with the analytes of the UDTs using the 2 urine dipsticks in different levels. The in vitro interference assay is not an ideal substitute for the confirmatory test. The collection of urine samples within 12-24 h of administration of RMP can prevent the interference caused by RMP and dRMP.