Home urine C‐peptide creatinine ratio (UCPCR) testing can identify type 2 and MODY in pediatric diabetes

Background Making the correct diabetes diagnosis in children is crucial for lifelong management. Type 2 diabetes and maturity onset diabetes of the young ( MODY ) are seen in the pediatric setting, and can be difficult to discriminate from type 1 diabetes. Postprandial urinary C‐peptide creatinine ratio ( UCPCR ) is a non‐invasive measure of endogenous insulin secretion that has not been tested as a diagnostic tool in children or in patients with diabetes duration <5 yr. We aimed to assess whether UCPCR can discriminate type 1 diabetes from MODY and type 2 in pediatric diabetes. Methods Two‐hour postprandial UCPCR was measured in 264 patients aged <21 yr (type 1, n = 160; type 2, n = 41; and MODY , n = 63). Receiver operating characteristic curves were used to identify the optimal UCPCR cutoff for discriminating diabetes subtypes. Results UCPCR was lower in type 1 diabetes [0.05 (<0.03–0.39) nmol/mmol median (interquartile range)] than in type 2 diabetes [4.01 (2.84–5.74) nmol/mmol, p < 0.0001] and MODY [3.51 (2.37–5.32) nmol/mmol, p < 0.0001]. UCPCR was similar in type 2 diabetes and MODY (p = 0.25), so patients were combined for subsequent analyses. After 2‐yr duration, UCPCR  ≥ 0.7 nmol/mmol has 100% sensitivity [95% confidence interval ( CI ): 92–100] and 97% specificity (95% CI : 91–99) for identifying non‐type 1 ( MODY  + type 2 diabetes) from type 1 diabetes [area under the curve ( AUC ) 0.997]. UCPCR was poor at discriminating MODY from type 2 diabetes ( AUC 0.57). Conclusions UCPCR testing can be used in diabetes duration greater than 2 yr to identify pediatric patients with non‐type 1 diabetes. UCPCR testing is a practical non‐invasive method for use in the pediatric outpatient setting.