Fasting c-peptide and insulin-like growth factor-binding protein-1 levels help to distinguish childhood type 1 and type 2 diabetes at diagnosis

Abstract

Children with new onset diabetes (n = 175) were evaluated over 12-months. Patients were presumptively diagnosed with type 2 diabetes mellitus (T2DM) (n = 26) based on obesity, a relative with T2DM, the ability to wean from insulin, and absence of glutamic acid decarboxylase-65 (GAD-65) antibodies. We hypothesized that markers of insulinization at diagnosis, including fasting C-peptide and insulin-like growth factor-binding protein (IGFBP)-1, in addition to initial CO(2) levels and urine ketones, would help in distinguishing type 1 diabetes mellitus (T1DM) from T2DM. Children with T1DM (84 male, 65 female) had a mean age of 8.7 +/- 4.3 yr and a racial background of 78% white, 19% black, and 3% other. In contrast, children with T2DM (13 female, 13 male) had a mean age of 14.2 +/- 3.1 yr with a racial background of 58% black, 27% white, and 15% other. Fasting C-peptide level was 0.38 +/- 0.37 ng/mL in T1DM vs. 2.66 +/- 2.14 ng/mL in T2DM; a C-peptide of 0.85 ng/mL had 83% sensitivity in distinguishing T1DM from T2DM. Fasting IGFBP-1 level was 38.1 +/- 39.1 ng/mL (T1DM) vs. 3.6 +/- 4.5 ng/mL (T2DM); a value of 3.6 ng/dL could distinguish the two types of diabetes with 93% sensitivity. Urinary ketones were found in 79% of children with T1DM compared with 56% of those with T2DM, and the magnitude was associated with type of diabetes. Initial CO(2) level for T1DM was 17.9 +/- 6.9 mmol/L vs. 22.7 +/- 5.7 mmol/L for T2DM; a value of 21.5 mmol/L could distinguish the two types of diabetes with 83% sensitivity. In addition to obesity, family history of T2DM, and absence of GAD-65 antibodies, children with new-onset T2DM may be distinguished from those with T1DM by a combination of biochemical parameters (C-peptide, IGFBP-1, CO(2), and urine ketones).