Urine C-peptide, beta-cell function, and insulin requirement.

Urinary C-peptide excretion was investigated as a method for monitoring beta-cell function in diabetic patients and for studying the contribution of endogenous insulin production to diabetic control. Control subjects had variations in serum and urine C-peptide immunoreactivity that correlated with basal and meal-related insulin secretion. In a group of well-controlled juvenile diabetic patients, those receiving high doses of insulin had low or negligible C-peptide excretion, whereas most patients with low exogenous insulin requirements had near-normal urinary C-peptide excretion. Patients treated for diabetic ketoacidosis had recovery of beta-cell function as measured by C-peptide immunoreactivity in serial urine specimens. Thus, measurement of urinary C-peptide excretion is a simple technique that may be useful in assessing endogenous insulin production in juvenile diabetic patients.