## Acid-Base and Biochemical Parameters in DKA ### Correct Diagnostic Criteria | Parameter | DKA Range | Clinical Significance | |-----------|-----------|----------------------| | Arterial pH | <7.30 (often <7.25) | Severe acidemia; pH >7.30 suggests mild DKA or mixed process | | Serum HCO₃⁻ | <15 mEq/L (often <10) | Reflects severity of metabolic acidosis | | Anion gap | >12 mEq/L | High anion gap metabolic acidosis from ketoacid accumulation | | Serum osmolality | 300–320 mOsm/kg | Hyperglycemia and hypernatremia drive osmolality up | | β-hydroxybutyrate | >3 mmol/L | Gold standard for ketosis diagnosis | **Key Point:** The hallmark of DKA is **arterial pH <7.30**, not >7.30. A pH >7.30 rules out moderate-to-severe DKA and suggests either mild DKA or another diagnosis (e.g., starvation ketosis, lactic acidosis). ### Why the Distractor Is Wrong Arterial pH >7.30 is **incompatible with the diagnostic definition of DKA**. The diagnostic triad requires: 1. pH <7.30 2. HCO₃⁻ <15 mEq/L 3. Positive serum/urine ketones with anion gap >12 If pH is >7.30, the patient does not meet criteria for DKA and alternative diagnoses must be considered. **High-Yield:** Remember the **"3-15-12" rule** for DKA: - pH <7.30 - HCO₃⁻ <15 mEq/L - Anion gap >12 mEq/L ### Osmolality in DKA Despite severe hyperglycemia (often 250–600 mg/dL), serum osmolality in pure DKA typically ranges **300–320 mOsm/kg**. This is because: - Hyperglycemia raises osmolality - But concurrent volume depletion and electrolyte losses partially offset this - HHS (hyperglycemic hyperosmolar state) shows osmolality >320 mOsm/kg due to even higher glucose levels with less ketosis **Clinical Pearl:** A patient with pH >7.30 and elevated glucose should prompt investigation for HHS or mixed metabolic derangements, not uncomplicated DKA. [cite:Harrison 21e Ch 417]
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