Background There is currently no reliable indicator of inflammation available for the evaluation of genital tract syndromes. We investigated the association of urinary calprotectin concentration, an innate immune system mediator protein, with urethritis.
Methods First catch urine specimens from men with and without urethritis (> 10 neutrophils/high power field of urethral smears) were tested for Neisseria gonorrhoeae (NG), Chlamydia trachomatis (CT), Mycoplasma genitalium (MG) and Trichomonas vaginalis (TV) by nucleic acid amplification tests (NAAT). Supernatants from these samples were tested in duplicate by ELISA for human calprotectin. Data were analysed using Spearman’s coefficient of rank correlation (rho) and ROC curves.
Results 159 urinary supernatants were tested. 54/159 had urethritis; 35/159 were NAAT positive for any of CT, NG, MG or TV of whom 27/35 had urethritis; 97/159 had no urethritis and were NAAT negative for all 4 pathogens. The correlation coefficient (rho) for calprotectin concentration and presence of urethritis/infection was 0.529 (95% CI: 0.407–0.633; p < 0.0001) with a calprotectin concentration of 95ng/mL (95% CI: 65–119.64ng/mL ROC curve AUC: 0.811, 95% CI: 0.741–0.869 p < 0.001) having a sensitivity of 0.771 (95% CI: 0.594–0.949) and specificity of 0.831 (95% CI: 0.746–0.915) compared to a sensitivity and specificity of urethral smears of 0.771 (95% CI: 0.594–0.949) and 0.782 (95% CI: 0.69–0.875) respectively in detecting CT, NG, MG or TV infections. The calprotectin assay had sensitivity and specificity of 0.629 (95% CI: 0.476–0.782) and 0.907 (95% CI: 0.834–0.981) respectively for detecting urethritis.
Conclusion Urinary calprotectin had similar sensitivity and specificity for common urethral pathogens as urethral microscopy. Low calprotectin concentration correlated well with the absence of inflammation. Use of the assay is currently limited by the unknown dilution effect of urine in estimating urethral calprotectin concentrations but calprotectin is a promising biomarker of inflammation in investigating reproductive tract infections (RTI) of different aetiologies particularly where microscopy may not be available, such as in community settings.
- Inflammatory biomarker