The need to feed? Is a blood glucose above 8 mmol/L needed for the correct interpretation of C-peptide in patients with diabetes?

Abstract

Introduction: C-peptide measurement has found utility in the classification of diabetes, with a random C-peptide <0.6 nmol/L suggestive of insulin deficiency and type 1 diabetes, and a concentration <0.2 nmol/L confirming absolute insulin deficiency.1 However, there is doubt if random C-peptide when the blood glucose (BG) is <8 mmol/L still retains predictive value for assessing insulin deficiency.1,2 We assessed the ability of C-peptide <0.2 and <0.6 nmol/L to predict autoimmune diabetes (defined by GAD/IA2 antibody positivity) when BG is above or below 8 mmol/L and the effect of fasting on achieving a BG above this threshold.