Urinary Excretion of Total Proteins, Albumin, and β₂-Microglobulin During Rest and Exercise in Diabetic Adolescents With and Without Retinopathy

To determine whether protein excretion during exercise is an earlier sign of renal dysfunction in diabetic adolescents than the basal measurements, urinary creatinine, total proteins, albumin, and β₂-microglobulin were studied before, immediately after, and 30 min after exercise until exhaustion on a bicycle ergometer in a group of 21 adolescent diabetic boys (Albustix negative) and in a comparable control group. Among the 21 diabetic subjects, 11 had an incipient retinopathy diagnosed by fluorescein angiography. Urinary output of creatinine was similar in diabetic and in nondiabetic groups, and did not vary during exercise. At rest, the urinary output of total proteins, albumin, and β₂-microglobulin was signify cantly higher in diabetic subjects than in controls. These data suggest that the subclinical proteinuria of diabetes is of mixed origin, being both glomerular and tubular. An exercise test leading to exhaustion did not give any additional information other than the basal excretion. There was no difference between diabetic subjects with early retinal vascular changes and those free from all retinopathy.