Tamm-Horsfall-Protein excretion as a marker of ascending limb transport indicates early renal tubular damage in diabetes mellitus type I

Tamm-Horsfall Protein (THP) is a 95 kD glycoprotein which is secreted in the thick ascending loop of Henle (TALH) of the kidney. After renal tubular damage the secretion of THP is reduced. In diabetes mellitus (DM), TALH has not been studied. To differentiate between glomerular (albumin), proximal tubular microglobulinuria (α₁-microglobulin), and TALH function (THP), we investigated 65 patients 4–61 years of age. In well-controlled DM, mean hemoglobin A₁ equalled 7.4% and proximal tubular parameters indicated reversible damage early after onset. THP excretion (per 24 hrs or per day) was significantly elevated in DM duration of greater than ten years, suggesting enhanced TALH ion transport (glomerular hyperfiltration). THP secretion decreased in DM duration of greater than 15 years despite normal albumin excretion. Thus, renal THP excretion indicates early medullary dysfunction (TALH) in DM type I.