Plasma and urinary C-peptide in the classification of adult diabetics

Abstract

Plasma and urinary C-peptide determinations in the discrimination between insulin-requiring and non-insulin-requiring diabetes were elevated in 61 adult diabetics. Specimens for C-peptide determinations were taken on two consecutive days: on the first day plasma C-peptide concentrations were determined before and 6 min after intravenous glucagon administration. On the second day 2- and 4-h urinary C-peptide excretion was measured after an individual breakfast. Results of urinary C-peptide analyses were expressed as molar concentration and also as molar quantity excreted (without any corrections and related to creatinine excretion). Glucagon-stimulated plasma C-peptide turned out to be a reliable criterion for the detection of insulin requirement. Sixty-nine per cent of diabetics included in this study were classifiable by basal plasma C-peptide concentrations. Two-hour postprandial urinary C-peptide/creatinine quotient turned out to be slightly less sensitive (89%) than the glucagon test (94%) and of equal specificity (96%). Glucagon-stimulated plasma C-peptide and postprandial urinary C-peptide excretion correlated significantly among insulin-requiring diabetics (r = 0.73), but not among non-insulin-requiring diabetics (r = 0.23). We regard determination of stimulated plasma C-peptide as a primary investigation for the direct assessment of endogenous insulin secretory reserves for clinical management decisions. Determination of postprandial urinary C-peptide is applicable in selected situations for non-invasive assessment of insulin secretion.

Fasting plasma C-peptide, glucagon stimulated plasma C-peptide, and urinary C-peptide in relation to clinical type of diabetes

“…Thus, the predictive value of a stimulated C-peptide level above and below 0.60 nmol/1 as indicator of Type 2 and Type 1 diabetes was 91% and 78%, respectively. A plasma C-peptide level of 0.60 nmol/1 has previously been suggested to discriminate between Type 2 diabetic subjects with and without insulin requirement [8,9]. In our study, approximately 75% of patients with a stimulated plasma C-peptide concentration from 0.32 nmol/1 to 0.60 nmol/1 were clinically Type 2 diabetic subjects.…”

“…Similarly, Koskinen et al reported that urinary C-peptide was less H. J. Gjessing et al: C-peptide and clinical type of diabetes sensitive than post glucagon C-peptide in the discrimination between Type 2 diabetic subjects with and without insulin requirement [9]. The most important reason probably is a large variability of urinary C-peptide excretion [14].…”

“…The test has now become widely used in patients with Type 1 diabetes [4][5][6][7][8][9] but also in patients with Type 2 diabetes mellitus [8][9][10][11]. The test has also been used in attempts to discriminate between Type 2 diabetic patients with and without insulin requirement in order to control hyperglycaemia [8,9].…”

Detection of C-Peptide in Urine as a Measure of Ongoing Beta Cell Function

“…Urine samples collected over a period of four hours and single post stimulated UCP have been shown to be significantly correlated with serum insulin and serum C-peptide in non-diabetic subjects 26 , and in insulin treated diabetic patients 7 . Correcting for creatinine adjusts urine C-peptide concentration for variation in urine concentration and enables the use of 'spot' urine samples in place of 24-h urine collection.…”

“…There is extensive evidence that C-peptide can be used to differentiate between the classification of Type 1 diabetes and Type 2 diabetes [6][7][8][9][10] . C-peptide is a good candidate biomarker to differentiate patients with Maturity Onset Diabetes of the Young (MODY) from Type 1 diabetes.…”