A 28-year-old woman with type 1 diabetes mellitus presents to the emergency department with a 2-day history of polyuria, polydipsia, and progressive lethargy. On examination, she has Kussmaul respirations and a fruity smell on her breath. Capillary blood glucose is 450 mg/dL. Which investigation is most specific for confirming the diagnosis of diabetic ketoacidosis?

## Diagnosis of DKA: Role of Ketones **Key Point:** Beta-hydroxybutyrate is the MOST SPECIFIC and GOLD STANDARD investigation for confirming DKA. It is the predominant ketone body produced in DKA (accounts for ~70% of total ketones) and directly reflects the severity of ketoacidosis. ### Why Beta-Hydroxybutyrate? **High-Yield:** Serum beta-hydroxybutyrate is: - The primary ketone body in DKA (more specific than acetoacetate or acetone) - Quantifiable and correlates with disease severity - More reliable than urine ketones (which may be negative early in DKA or remain positive after resolution) - The investigation that CONFIRMS the metabolic derangement ### Diagnostic Criteria for DKA | Feature | Finding | |---------|----------| | **Blood glucose** | Usually 250–600 mg/dL (can be <250 in euglycemic DKA) | | **Arterial pH** | <7.35 | | **Serum bicarbonate** | <18 mEq/L | | **Anion gap** | >12 (metabolic acidosis) | | **Serum/urine ketones** | **Positive (beta-hydroxybutyrate >3 mmol/L confirms DKA)** | **Clinical Pearl:** While ABG/bicarbonate and anion gap are NECESSARY to assess severity and guide treatment, they are NOT specific for DKA — they reflect metabolic acidosis from ANY cause. Ketones are the SPECIFIC marker of ketoacidosis. **Mnemonic: DKA Diagnosis** — **BKAG** - **B**eta-hydroxybutyrate (elevated; most specific) - **K**etones (serum/urine positive) - **A**nion gap (elevated; >12) - **G**lucose (elevated; >250) ### Diagnostic Algorithm ```mermaid flowchart TD A[Suspected DKA: polyuria, polydipsia, Kussmaul respirations]:::outcome A --> B[Check capillary/serum glucose]:::action B --> C{Glucose elevated?}:::decision C -->|Yes| D[Check ABG/VBG for pH and HCO3-]:::action D --> E{pH <7.35 AND HCO3- <18?}:::decision E -->|Yes| F[Measure serum beta-hydroxybutyrate]:::action E -->|No| G[Consider other diagnosis]:::outcome F --> H{Beta-hydroxybutyrate >3 mmol/L?}:::decision H -->|Yes| I[DKA CONFIRMED]:::outcome H -->|No| J[Unlikely DKA]:::outcome C -->|No| K[Reconsider diagnosis]:::outcome ``` **Warning:** Urine ketones may be NEGATIVE early in DKA or remain positive for days after resolution — they are less reliable than serum beta-hydroxybutyrate.