Measurement of urinary TGF-β1 in patients with diabetes mellitus and normal controls.

Objective: Increasing evidence links TGF-β1 to progression of renal fibrosis including its association with diabetic nephropathy (DN). Current ELISA assays are not sensitive enough to measure TGF-β1 in the urine of many clinically healthy individuals, even those with established renal disease. The objective of this study was to validate a sensitive urinary assay for TGF-β1 and compare levels between healthy controls and patients with established DN.

Design And Methods: An ELISA method (R&D Systems) was utilized together with an amplification step to assay TGF-β1 in urine samples from 190 patients with DN and 80 healthy controls.

Results: Using an ELAST (Perkin Elmer, Inc) amplification step, the ELISA for urinary TGF-β1 had a limit of quantification of 15.6 pg/mL and limit of detection of 7 pg/mL. Preliminary studies demonstrated that TGF-β1 was stable if urine was frozen promptly at -70°C without preservatives. Using this assay, 22/80 controls (27%) had detectable levels of urinary TGF-β1 (range <7 to 40.9 pg/mL; mean±SD 6.4±11.1 pg/mL). This was significantly lower (p<0.0001) than in the DN group in whom 114/190 (60%) had detectable levels of urinary TGF-β1 (range <7 to 526.4 pg/mL; mean±SD 20.4±45.8 pg/mL). Urinary protein and TGF-β1 concentrations demonstrated modest correlation in patients with DN (r=0.47, P<0.001). TGF-β1 measurement in patients with DN did not demonstrate significant association with progression of proteinuria or increase in serum creatinine during the next 12 months of follow-up.

Conclusion: We have validated a sensitive ELISA assay for urinary TGF-β1, and demonstrated correlations with the degree of proteinuria and higher levels in patients with DN compared to controls. Additional study will be necessary in order to determine if serial testing can predict renal prognosis independent of known prognostic factors for patients with DN.