Routine blood test monitoring of complete blood count (CBC), serum electrolytes, or creatinine is not warranted for young children receiving long-term prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMZ) for recurrent urinary tract infections (UTIs), investigators concluded in a paper published in Clinical Pediatrics.

Milan Dattaram Nadkarni, MD, of Wake Forest University in Winston-Salem, North Carolina, and colleagues analyzed data from the prospective randomized, placebo-controlled RIVUR trial, which enrolled 607 children aged 2 to 71 months who had vesicoureteral reflux (VUR) diagnosed after symptomatic UTIs. In that trial, investigators randomly assigned 302 patients to receive TMP-SMZ and 305 to receive placebo and followed up with patients for 24 months.

Investigators measured CBC, serum electrolytes, and creatinine at baseline and at the 24-month study conclusion. Dr Nadkarni’s team reported finding no significant hematologic, electrolyte, or renal abnormalities between the treatment and placebo groups.

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“In conclusion, our study did not reveal any adverse effect of TMP-SMZ prophylaxis on CBC, serum electrolytes, and creatinine,” the authors concluded. “As a result, we do not recommend any such routine laboratory tests in otherwise healthy children who are on long-term prophylaxis with TMP-SMZ for VUR or any other medical condition.”

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The large number of patients who received TMP-SMZ in a prospective, randomized controlled trial was a strength of the study, Dr Nadkarni’s team stated. The study had limitations, however. Laboratory abnormalities were a secondary end point and local laboratories rather than a single center performed the tests, and laboratory tests often were ordered at the discretion of treating physicians. Some patients refused to have follow-up laboratory tests, resulting in missing laboratory values.


Nadkarni MD, Mattoo TK, Gravens-Mueller L, et al. Laboratory findings after urinary tract infection and antimicrobial prophylaxis in children with vesicoureteral reflux [published online December 31, 2019]. Clin Pediatr.

doi: 10.1177/0009922819898185