Residual B cell function in diabetic children as determined by urinary C-peptide.

C-peptide was determined in 24-h urine collections and in fasting plasma of 27 Type 1 (insulin-dependent) diabetic children (duration of disease 0-6 years) and in 11 matched normal children. Grouping the patients according to duration of disease from onset to 6 years, it was found that in the first year of disease the B cell reserve was a mean of 4.89 +/- 1.95 pmol X mg creatinine-1. 24 h-1 compared with a mean of 24.51 +/- 2.91 pmol X mg-1 X 24 h-1 in the control group. A further diminution was seen with increase in the duration of disease, until after 6 years when only traces of C-peptide could be detected. There was a good correlation between the levels of plasma C-peptide and urinary C-peptide values as related to creatinine (r = 0.89; p = less than 0.001). In view of this, and since it is simpler and less traumatic to obtain frequent urine samples from children than it is to obtain blood samples, it was felt that the determination of urinary C-peptide constitutes a valuable tool in the evaluation of the diabetic child.