Investigating the Diagnostic Utility of C-Peptide in Diabetes Mellitus: A Cross-Sectional Study in a Tertiary Health Facility in Edo State, Nigeria

Chronic hyperglycemia, a hallmark of diabetes mellitus (DM), necessitates proper classification for effective management, a task often complicated by misdiagnosis, especially where resources are limited. This research aimed to investigate the diagnostic utility of C-peptide, a marker of endogenous insulin secretion, in patients at a tertiary medical facility in Edo State, Nigeria. Using a cross-sectional design, three groups—Type 1 DM, Type 2 DM, and non-diabetic controls had their serum C-peptide levels measured and compared. Blood pressure and anthropometric data were also recorded. The discriminative power of C-peptide for DM classification was evaluated using ROC curve analysis. Findings revealed that C-peptide levels were significantly lower in Type 1 DM patients (mean = 0.1935 ng/mL) compared to Type 2 DM (1.3067 ng/mL) and controls (1.9064 ng/mL), with Type 2 DM subjects showing intermediate levels indicative of partial β-cell function. No discernible variation in C-peptide levels by gender was observed. ROC analysis demonstrated excellent discriminatory power for identifying Type 1 DM (AUC = 0.002), with this value indicating that a low C-peptide level is highly predictive of the disease. The analysis also showed good discriminatory power for Type 2 DM (AUC = 0.265). In conclusion, C-peptide measurement proves to be a valid and affordable biomarker for differentiating diabetes mellitus types. It is particularly useful for detecting absolute insulin insufficiency in Type 1 DM, thus advocating for its integration into routine clinical evaluation to enhance diagnostic precision and guide customized treatment plans.