Urinary vitamin D-binding protein is elevated in patients with endometriosis

Recently, proteomic technologies have demonstrated that several proteins are differently expressed in various body fluids of patients with endometriosis compared with those without this condition. The aim of this study was to investigate proteins secreted in urine of patients with endometriosis using proteomic techniques in order to identify potential markers for the clinical diagnosis of endometriosis.

Urine samples were collected from women undergoing laparoscopy for different indications including pelvic masses, pelvic pain, suspicious endometriosis, infertility and diagnostic evaluation. Proteomic techniques and mass spectrometry were used to identify proteins secreted in the urine of the patients with and without endometriosis and quantification of identified protein was performed using western blot and specific commercial sandwich enzyme-linked immunosorbent assays (ELISA).

Twenty-two protein spots were differentially expressed in the urine of patients with and without endometriosis, one of which was identified as urinary vitamin D-binding protein (VDBP). ELISA quantification of urinary VDBP corrected for creatinine expression (VDBP-Cr) revealed that urinary VDBP-Cr was significantly greater in patients with endometriosis than in those without (111.96 ± 74.59 versus 69.90 ± 43.76 ng/mg Cr, P = 0.001). VDBP-Cr had limited value as a diagnostic marker for endometriosis (Sensitivity 58%, Specificity 76%). When combined with serum CA-125 levels (the product of serum CA-125 and urinary VDBP-Cr), it did not significantly increase the diagnostic power of serum CA-125 alone.

Urinary VDBP levels are elevated in patients with endometriosis. They have limited value as a potential diagnostic biomarker for endometriosis but suggest it would be worthwhile to investigate other urinary proteins for this purpose.