Association of urinary type IV collagen with GFR decline in young patients with type 1 diabetes.

BACKGROUND Some patients with diabetes have advanced diabetic glomerular lesions and progressive kidney function decline even if urinary albumin levels are in the normal range. Therefore, another prognostic marker for diabetic kidney disease needs to be identified. We aimed to clarify whether urinary type IV collagen is associated with the progression of kidney function decline in patients with type 1 diabetes. STUDY DESIGN Hospital-based observational cohort study. SETTING & PARTICIPANTS 231 normo- and microalbuminuric patients with type 1 diabetes who were younger than 40 years at the start of the study. PREDICTOR & MEASUREMENTS: Urinary type IV collagen, determined using a 1-step sandwich enzyme immunoassay. OUTCOME The primary outcome measurement was rate of change in estimated glomerular filtration rate (eGFR). RESULTS Mean follow-up was 7.4 ± 1.3 (standard deviation) years. Urinary type IV collagen-creatinine ratio (T4C) was associated significantly with rate of change in eGFR in both univariate (r = -0.169; P = 0.01) and multivariate regression analyses (standardized estimate = -0.131; P = 0.03). In the sensitivity analysis limited to patients with normoalbuminuria (n = 213), T4C, but not urinary albumin-creatinine ratio (ACR), was associated significantly with rate of change in eGFR (standardized estimate = -0.12; P = 0.03). The interaction between logarithmically transformed ACR and logarithmically transformed T4C on eGFR decline was not significant (P for interaction = 0.2). We compared the adjusted rate of change in eGFR among 4 groups classified according to normal or increased T4C and ACR values and found that the rate of decline in eGFR in patients with increased T4C and normal ACR values was significantly faster than that in patients with normal T4C and ACR values (-4.3 and -3.0 mL/min/1.73 m(2)/y; P = 0.004, analysis of covariance). LIMITATIONS Study size was relatively small. CONCLUSIONS T4C is associated with progression of kidney function decline in young patients with type 1 diabetes.