2.1. Calculations and statistical analysis
Serum C-Peptide (C-Pep) from all samples was analyzed by ECLIA assay (Cobas Elecsys C-Peptide assay, Roche Diagnostics GmbH, Mannheim, Germany) in Beo-Lab laboratory, Belgrade (baseline normal C-Pep reference range: 1.10–4.40 ng/mL). Absolute increase in serum C-Pep (ΔC-Pep) was calculated as difference between postprandial and baseline C-Pep (ng/mL). ΔC-Pep greater than 2.4 ng/mL was considered significant [Postprandial C-Pep to postprandial glucose ratio (PCPG) was analyzed as a marker of beta cell reserve (mcg/mmol) [HOMA-IR = 1.5 + (FPG × FCP × 331.1) / 2800; HOMA-B = 0.27 × FCP × 331.1 / (FPG - 3.5).Results were presented as count (%), mean ± standard error of mean. Groups were compared for significance of difference using parametric (t-test) and nonparametric (chi-square, Mann–Whitney U, and Friedman) tests. To assess significance of correlation between variables, Pearson and Spearman correlations were used. SPSS Statistics v. 26 software was employed for the statistical analyses. p-values of less than 0.05 were regarded as indicating statistical significance.