Use of Serum Bicarbonate to Substitute for Venous pH in New-Onset Diabetes

Abstract

OBJECTIVE: To investigate whether serum bicarbonate (HCO3) levels can be used to accurately diagnose diabetic ketoacidosis (DKA) and classify its severity in children with new-onset diabetes mellitus (NODM). METHODS: Retrospective study of all patients with NODM presenting to Boston Children’s Hospital from October 1, 2007, to July 1, 2013. DKA was defined as blood glucose ≥200 mg/dL, venous pH (vpH) <7.3, and urine ketones ≥2+, and severe DKA as vpH <7.1. Linear regression was used to assess serum HCO3 as a predictor of vpH, and logistic regression to evaluate serum HCO3 as a predictor of DKA and severe DKA. RESULTS: Of 690 study cohort subjects (47% girls, age 10.8 ± 4.3 years, 76.7% white), 19.4% presented with DKA. The relationship between serum HCO3 and vpH was log-linear (r = 0.87, 95% CI 0.85–0.89, P < .001). HCO3 predicted vpH (R2 0.75, P < .001) using the formula vpH = 6.81301 + (0.17823*ln[HCO3]) and DKA and severe DKA (c-statistic 0.97 [95% CI 0.96–0.99, P < .001] and 0.99 [95% CI 0.991–0.999, P < .001], respectively). HCO3 cutoffs of <18 and <8 mmol/L had sensitivities of 91.8% and 95.2%, and specificities of 91.7% and 96.7%, respectively, to diagnose DKA and severe DKA. Findings were similar in a validation cohort of 197 subjects. CONCLUSIONS: Serum HCO3 concentration alone can substitute for vpH to diagnose DKA and classify severity in children with NODM. It is suggested as an alternative to reliance on vpH, especially in settings in which access to vpH measurement is limited.