Serum Type IV Collagen in Diabetic Patients at Risk for Nephropathy

Serum Type IV Collagen in Diabetic Patients at Risk for Nephropathy Margo P. Cohen , MD , Clyde W. Shearman , PHD and Gregory T. Lautenslager , PHD Institute for Metabolic Research, University City Science Center, Philadelphia, Pennsylvania Abstract OBJECTIVE —Whereas increased urinary excretion of type IV collagen, which is believed to reflect renal overproduction of this extracellular matrix protein in early diabetic nephropathy, has been confirmed in several studies, examination of serum concentrations of this analyte has yielded conflicting results. We sought to clarify the relationship between early renal dysfunction in diabetes and circulating type IV collagen concentrations. RESEARCH DESIGN AND METHODS —We measured serum (human) collagen IV concentrations by immunoassay in 109 patients with type 1 or type 2 diabetes and various amounts of albuminuria extending from the normo- to the macroalbuminuric range, and we examined its relationship to albumin excretion and to serum creatinine levels. RESULTS —Serum collagen IV concentrations (mean ± SEM) were not significantly different in normoalbuminuric (219 ± 10 ng/ml), microalbuminuric (209 ± 6 ng/ml), or macroalbuminuric (206 ± 7 ng/ml) diabetic subjects or in nondiabetic normal volunteers (206 ± 10 ng/ml). Collagen IV concentrations showed no significant correlation ( P > 0.25) with albumin excretion ( r = −0.001), HbA 1c ( r = 0.030), or serum creatinine ( r = −0.161) and were unrelated to urinary excretion of collagen IV in the subset of subjects in whom these data were available. CONCLUSIONS —The results of this cross-sectional analysis discount the utility of measurement of the serum concentration of collagen IV as an indicator of early renal dysfunction in diabetes. Increased urine excretion of collagen IV without a significant change in the serum concentration is consistent with a renal origin of this analyte in early diabetic nephropathy. A:C, albumin-to-creatinine ratio ADA, American Diabetes Association RSC, reciprocal of the serum creatinine value Footnotes Address correspondence and reprint requests to Margo P. Cohen, MD, IMR, University City Science Center, 3508 Market St., Philadelphia, PA 19104. Received for publication 18 January 2001 and accepted in revised form 26 April 2001. E-mail: drmpcohen{at}aol.com . A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.