The clinical utility of C‐peptide measurement in the care of patients with diabetes

Abstract

C-peptide is produced in equal amounts to insulin and is the best measure of endogenous insulin secretion in patients with diabetes. Measurement of insulin secretion using C-peptide can be helpful in clinical practice: differences in insulin secretion are fundamental to the different treatment requirements of Type 1 and Type 2 diabetes. This article reviews the use of C-peptide measurement in the clinical management of patients with diabetes, including the interpretation and choice of C-peptide test and its use to assist diabetes classification and choice of treatment. We provide recommendations for where C-peptide should be used, choice of test and interpretation of results. With the rising incidence of Type 2 diabetes in younger patients, the discovery of monogenic diabetes and development of new therapies aimed at preserving insulin secretion, the direct measurement of insulin secretion may be increasingly important. Advances in assays have made C-peptide measurement both more reliable and inexpensive. In addition, recent work has demonstrated that C-peptide is more stable in blood than previously suggested or can be reliably measured on a spot urine sample (urine C-peptide:creatinine ratio), facilitating measurement in routine clinical practice. The key current clinical role of C-peptide is to assist classification and management of insulin-treated patients. Utility is greatest after 3–5 years from diagnosis when persistence of substantial insulin secretion suggests Type 2 or monogenic diabetes. Absent C-peptide at any time confirms absolute insulin requirement and the appropriateness of Type 1 diabetes management strategies regardless of apparent aetiology.

Reduction of postprandial glucose by lixisenatide vs sitagliptin treatment in Japanese patients with type 2 diabetes on background insulin glargine: A randomized phase IV study (NEXTAGE Study)

“…Since increases in t max and t 1/2b of the gastric emptying rate were observed in the lixisenatide group vs the sitagliptin group, it is likely that slowing of gastric emptying was the driver for PPG reduction in this study, rather than insulinotropic effects. Indeed, greater exposure to postprandial C‐peptide (and hence insulin) was observed in the sitagliptin group than in the lixisenatide group, which is consistent with the inverse association of C‐peptide levels with glycaemic variability and with post‐meal glucose rise in T2D (both of which were higher in the sitagliptin group) 38. In previous studies, there was a direct relationship between PPG AUC after breakfast and gastric emptying with lixisenatide 20 µg once daily,32, 39 which was not observed with placebo 39…”

Continuing rise of Type 2 diabetes incidence in children and young people in the UK

“…Type 2 diabetes was distinguished from other types of diabetes using the following criteria: (1) presence of raised insulin level (>132 pmol/l) or raised C peptide level (>0.6 nmol/l) 13, 14 or (2) the child was managed off insulin therapy for >9 months in the absence of typical Type 1 diabetes auto‐antibodies. The latter definition is likely to be based on a clinical re‐evaluation after diagnosis when a clinical course suggests a diagnosis other than Type 1 diabetes.…”

Obstructive sleep apnoea and type 1 diabetes mellitus

“…Recently, urinary C-peptide is increasingly being used to differentiate type 1 from type 2 diabetes, although this test is more useful when done 3-5 years after diagnosis when the majority of patients with type 1 diabetes will have low C-peptide. 10 By definition, our patient has LADA. He had the typical phenotype of type 2 diabetes with positive GAD antibody and slowly progressive beta-cell failure requiring insulin after six months of diagnosis (our patient was commenced on insulin 15 months after diagnosis).…”