Abstract
Measurement of 24-h urine C-peptide immunoreactivity is a useful means of distinguishing patients with insulin-dependent (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM). However, 24-h complete urine collection is not always easy especially for ambulant patients. Therefore, amounts of C-peptide in fasting and postprandial (2h after breakfast) urine were measured and correlated with 24-h urine C-peptide excretion and serum C-peptide concentration.
The amount of postprandial urine C-peptide excretion (spot urine CPR), expressed as an urine CPR: urine creatinine ratio (μg) in normal subjects (n=7), those with IDDM (n=14) and those with NIDDM (n=29) were 55.1±32.6, 3.7±7.3 and 64.7±37.6 (mean±SD), respectively. The spot urine CPR in IDDM was significantly lower than that in NIDDM (p<0.001). In patients with IDDM spot urine CPR was less than 15μg/g in most cases.
There were highly significant correlations between fasting or postprandial spot urine CPR and 24-h urine CPR (r=0.66, r=0.67, p<0.001). There were also significant correlations between fasting or postprandial spot urine CPR and fasting or postprandial serum CPR (r=0.53, r=0.59, p<0.001). Correlation coefficients between fasting or postprandial serum CPR and 24-h urine CPR were also significant but they were lower than those between spot urine CPR and 24-h urine CPR.
These results suggest that, despite some limitations, the spot urine CPR can be used as an additional index of insulin dependency in diabetic patients. A postprandial spot urine CPR value of less than 15μg/g would suggest that the patient is likely to be insulin-dependent.
