Erythrocyte sodium-hydrogen antiport activity is not a predictor of diabetic nephropathy

Erythrocyte sodium-hydrogen antiport activity was measured by Orlov's method in 36 healthy volunteers (18 with negative, 18 with positive family history of hypertension) and 52 subjects with type 1 insulin-dependent diabetes mellitus: 29 patients were without known diabetic complications, 23 patients with microangiopathy (10 with diabetic retinopathy, 13 with 'incipient' diabetic nephropathy). Normotensive healthy adults had similar antiport activities independently of a positive or negative family history of hypertension (6.45 +/- 2.61 vs. 5.80 +/- 3.07 mmol/l of cells per h, respectively). Sodium-hydrogen antiport resulted 8.38 +/- 3.91 mmol/l of cells per h in the 29 uncomplicated diabetic patients, significantly higher (p < 0.05) compared to healthy subjects, both without and with family hypertension. Complicated diabetics confirmed to have an exchange rate higher than healthy controls (8.18 +/- 2.50 mmol/l of cells per h, p < 0.01): patients with retinopathy showed the highest antiport activity (8.96 +/- 2.95 mmol/l of cells per h, p < 0.01), while patients with nephropathy had milder antiport overactivity (7.58 +/- 2.02 mmol/l of cells per h), not significantly different from either uncomplicated diabetics or healthy controls. Thus, an increased sodium-hydrogen exchange rate in peripheral erythrocytes does not seem to be an early indicator of diabetic nephropathy.