False positive hCG testing and upper urinary tract infection.

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Human chorionic gonadotropin (hCG) assays are commonly used as a pregnancy test. False-positive human chorionic gonadotropin (hCG) values in urine were reported in 15 patients (nine males and six females) presenting with urinary tract infection. Extopic hCG production and presence of heterophilic antibodies were excluded as potential causes of interference. Orbitrap mass spectrometry revealed the presence ofuromodulin, an abundant urinary glycoprotein, as the likely cause of the interference. Falsely elevated hCG values correlated well with urinary alpha 1 microglobulin (a tubular protein) concentrations and with the urinary leukocyte count. The false positive hCG signal disappeared after antibiotic administration. These data suggest that false-positive hCG test results in urine may occur in patients presenting with upper urinary tract infections due to uromodulin interference.