Diagnostic Testing During Acute Diabetic Ketoacidosis

Rationale for Testing

The American Diabetes Association and other guidelines suggest that C-peptide, islet antibodies, and insulin levels should be sent during the acute DKA event to support diabetes classification, with the primary goal of distinguishing autoimmune type 1 diabetes from other forms of diabetes, which has critical implications for long-term management and patient counseling 1, 2

C-peptide level should be measured during the acute event to assess endogenous insulin production, and insulin level should be sent to support the diagnostic workup, along with standard DKA labs such as urine ketones, acid-base status, electrolytes, and glucose 1, 2
Islet autoantibodies, including anti-GAD, IA-2, IA-2b, and ZnT8 antibodies, should be sent to confirm autoimmune type 1 diabetes 3, 4

A C-peptide level of <200 pmol/L (<0.6 ng/mL) is consistent with type 1 diabetes, while a level of 200-600 pmol/L (0.6-1.8 ng/mL) may indicate type 1 diabetes, MODY, or insulin-treated type 2 diabetes, and a level of >600 pmol/L (>1.8 ng/mL) suggests type 2 diabetes or ketosis-prone type 2 diabetes 5, 6
Positive anti-GAD, IA-2, or ZnT8 confirms autoimmune type 1 diabetes regardless of C-peptide level, while negative antibodies do not exclude type 1 diabetes 3, 6

The American Diabetes Association and other guidelines recommend never delaying insulin therapy while waiting for antibody or C-peptide results, and treating the DKA according to standard protocols immediately 1, 2
These tests inform long-term management decisions, not acute treatment, and patients with ketosis-prone type 2 diabetes may eventually discontinue insulin after DKA resolution 1, 6