What is the most likely cause of a patient's condition presenting with vomiting, diarrhea, lethargy, and a nail polish-like breath odor, alongside hyperglycemia and hyponatremia?

Diabetic Ketoacidosis (DKA)

The most likely diagnosis is Diabetic Ketoacidosis (DKA), not hyponatremia, based on the characteristic nail polish-like (acetone) breath odor, which is pathognomonic for ketosis, combined with vomiting, lethargy, and the clinical presentation of acute metabolic decompensation. 1

Key Diagnostic Features Present

The nail polish-like breath odor is the critical diagnostic clue that distinguishes this case:

• Acetone breath (fruity/nail polish odor) is specific for ketosis and indicates DKA, not simple hyperglycemia or isolated hyponatremia 1, 2
• Vomiting accompanied by hyperglycemia and signs of ketosis indicates DKA, which is a life-threatening condition requiring immediate medical care 1, 3
• The altered mental status (drowsy but arousable) is consistent with DKA, where mental status changes range from lethargy to coma 1, 4
• Mild hypotension reflects the hypovolemia from osmotic diuresis that invariably accompanies DKA 1, 2

Why Not the Other Options

Hyponatremia (Option C) is a red herring in this case:

• The serum sodium of 124 mmol/L is actually pseudohyponatremia caused by the hyperglycemia itself 5, 6
• The corrected sodium must be calculated by adding 1.6 mEq/L for each 100 mg/dL glucose above 100 mg/dL 5
• With glucose of 8.9 mmol/L (160 mg/dL), the corrected sodium is approximately 125 mmol/L, which is near-normal 5
• DKA and HHS typically present with normal or low sodium due to hyperglycemia-induced dilutional effects, not true hyponatremia 1, 6

Uncontrolled Hyperglycemia (Option B) is insufficient:

• The glucose of 8.9 mmol/L (160 mg/dL) is only mildly elevated and does not explain the acetone breath 1
• Simple hyperglycemia without ketosis does not produce the characteristic fruity/nail polish breath odor 2

Hyperosmolar Hyperglycemic State (Option D) is excluded:

• HHS requires glucose ≥600 mg/dL (33.3 mmol/L), whereas this patient has only 160 mg/dL 1
• HHS does not produce ketosis or acetone breath because residual insulin prevents lipolysis and ketogenesis 1
• The presence of acetone breath definitively rules out HHS 1, 2

DKA Diagnostic Criteria

According to American Diabetes Association guidelines, DKA diagnosis requires 1, 7:

• Plasma glucose >250 mg/dL (or euglycemic DKA with glucose <200 mg/dL in 10% of cases) 1
• Arterial pH <7.3 1
• Serum bicarbonate <18 mEq/L 1
• Positive serum or urine ketones 1
• Anion gap >10 mEq/L 1, 5

Important caveat: Approximately 10% of DKA cases present as euglycemic DKA (glucose <200 mg/dL), which can occur with reduced food intake, vomiting, pregnancy, or alcohol use 1. The presence of acetone breath with vomiting and altered mental status is sufficient to suspect DKA even with relatively modest hyperglycemia 1, 3.

Immediate Management Required

This patient requires urgent evaluation and treatment 1, 3:

• Obtain arterial blood gas, serum ketones (beta-hydroxybutyrate preferred), complete metabolic panel, and anion gap immediately 5, 7
• Begin isotonic saline (0.9% NaCl) at 15-20 mL/kg/hour (1-1.5 liters in first hour) for volume resuscitation 5
• Start continuous intravenous insulin infusion once DKA is confirmed 1, 3
• Monitor blood glucose every 1-2 hours and electrolytes frequently 5
• Never discontinue insulin even if the patient cannot eat, as this precipitates or worsens DKA 3

Critical Pitfall to Avoid

Do not be distracted by the low sodium level—this is expected in hyperglycemic states and does not represent the primary pathology 5, 6. The acetone breath is the pathognomonic finding that points directly to ketosis and DKA 1, 2.