Diabetic Ketoacidosis: Confirming Acidosis
A 9-year-old boy is brought to the emergency department with three days of polyuria, polydipsia and 3 kg weight loss, and one day of vomiting and abdominal pain. He is drowsy but rousable, his respiratory rate is 38 breaths/min with deep unlaboured breathing, heart rate is 132 beats/min, blood pressure is 96/58 mm Hg, and his breath smells fruity. A bedside capillary glucose reads 28 mmol/L (504 mg/dL) and a bedside blood beta-hydroxybutyrate is 5.4 mmol/L. Which of the following is the most appropriate investigation to confirm the diagnosis?
- A.Venous blood gas with serum bicarbonateCorrect
- B.Glycated hemoglobin measurement
- C.Serum sodium and calculated osmolality
- D.Random serum C-peptide and insulin level
Explanation
The ISPAD 2022 consensus guideline defines diabetic ketoacidosis by three biochemical criteria that must all be present: hyperglycemia above 11 mmol/L (200 mg/dL), ketonemia or ketonuria, and metabolic acidosis with a venous pH below 7.3 or serum bicarbonate below 18 mmol/L. This boy already has documented hyperglycemia and a blood beta-hydroxybutyrate above the 3 mmol/L threshold, and his deep Kussmaul respiration is the clinical signature of acidosis, so the only missing element is objective confirmation of the acidosis by a blood gas with bicarbonate. A venous sample is sufficient in children and spares an arterial puncture, since venous pH runs only about 0.02 to 0.03 units below arterial pH. The same result grades severity as mild, moderate, or severe, which determines the fluid and insulin plan, the need for intensive care, and the estimated risk of cerebral injury. Glycated hemoglobin documents chronic hyperglycemia over the preceding 2 to 3 months and confirms that diabetes is not new-onset stress hyperglycemia, but it neither establishes nor excludes ketoacidosis and does not alter acute management. Serum sodium and effective osmolality are important for calculating corrected sodium and for monitoring the fall in osmolality during therapy, yet a normal value does not exclude ketoacidosis. C-peptide, insulin, and islet autoantibody testing classify the type of diabetes at a later outpatient visit and have no role in the emergency evaluation. Electrolytes, urea, creatinine, and an electrocardiogram for hypokalemia should be sent alongside the gas, and insulin is withheld until at least 1 hour of fluid resuscitation has begun.
Why each option
- A.
- Correct. Venous pH and bicarbonate confirm the metabolic acidosis that completes the diagnostic triad and grade severity.
- B.
- Glycated hemoglobin reflects glycemic control over months and has no role in diagnosing an acute ketoacidotic crisis.
- C.
- Sodium and osmolality guide fluid therapy and monitoring but do not establish or exclude ketoacidosis.
- D.
- C-peptide and insulin classify the diabetes type at a later visit and are not emergency investigations.
Reference: Glaser N, et al. ISPAD Clinical Practice Consensus Guidelines 2022: Diabetic ketoacidosis and hyperglycemic hyperosmolar state. Pediatr Diabetes. 2022;23(7):835-856
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