Validation of an enzyme-linked immunosorbent assay for C-peptide analysis in Cameroon

Aims: To validate an ELISA method for C-peptide analysis in Cameroon. Methods: We evaluated the linearity, detection limit, functional sensitivity, precision and accuracy, and further investigated for cross-reactivity by proinsulin, and interferences by lipids, bilirubin and hemoglobin. This method was compared with the Roche electrochemiluminescence immunoassay. C-peptide stability was assessed following a series of freeze-thaw cycles, and after storage at room temperature. The C-peptide reference range was determined by analyzing fifty plasma samples of Cameroonians without diabetes. Results: The ELISA was linear at least up to 7.09μg/L, and had a detection limit of 0.09μg/L, and a functional sensitivity of 0.32μg/L. The inter- and intraassay %CV were 2.9-9.9%, and 5.2-9.4%, respectively. Recoveries were 81-94% in serum, and 93-98% in buffer. Comparison with the ECLIA yielded a good correlation coefficient (R2=0.98). There was no cross-reactivity with proinsulin, and no interference with lipids, bilirubin and hemoglobin. C-peptide was stable at room temperature for 24h and up to 7 freeze-thaw cycles for medium (1-6μg/L) and high (>6μg/L) levels (<-15°C and <-70°C). The reference range for C-peptide was 0.38-3.63μg/L. Conclusions: This method is suitable for C-peptide analysis in low-income countries like Cameroon. © 2012 Elsevier Ireland Ltd.