The use of urine protein 1 as an indicator of renal tubular function in type I (insulin-dependent) diabetes.

Abstract

One hundred male insulin-dependent diabetic patients, aged 16 to 85 (mean 51.9) years, with albumin excretion ranging from normal to gross excess were examined for glomerular and tubular functional alterations by estimating urinary levels of albumin and indicator proteins of tubular damage. Urine protein 1 (UP1), a newly-discovered low-molecular weight alpha-2 glycomicroglobulin, together with alpha 1-microglobulin was used to assess tubular function. 19% of the patients showed increased albumin excretion with normal levels of tubular proteins (glomerular proteinuria), 11% excreted only tubular proteins in excess (tubular proteinuria), while 40% had a mixed pattern of both increased albumin and tubular proteins (glomerulotubular or mixed proteinuria). 30% had normal albumin and tubular protein excretion in urine. UP1 was found to be a more sensitive indicator of tubular abnormality than alpha 1-microglobulin. It is concluded that, although glomerular changes may be responsible for the proteinuria seen in most diabetics (mixed proteinuria), in a small but significant proportion of diabetics, tubular functional alteration may occur before, or in the absence of, glomerular dysfunction, and may warn of subclinical tubular abnormality. This finding may have a direct bearing on the development and course of progression of diabetic nephropathy, and may question the reliability of the present prognostic interpretation of microalbuminuria.