How can I differentiate hyperosmolar hyperglycemic state (HHS) from diabetic ketoacidosis (DKA) based on clinical and laboratory findings?

Differentiating HHS from DKA: Laboratory and Clinical Criteria

The key to distinguishing HHS from DKA lies in three critical laboratory values: serum osmolality (≥320 mOsm/kg in HHS), absence of significant ketosis (ketones small or absent in HHS vs. positive in DKA), and lack of metabolic acidosis (pH >7.30 and bicarbonate ≥15 mEq/L in HHS vs. pH <7.30 and bicarbonate <15 mEq/L in DKA). 1

Laboratory Diagnostic Criteria

DKA Criteria 1

• Plasma glucose: ≥250 mg/dL
• Arterial pH: <7.30 (ranges from 7.25-7.30 for mild, 7.00-7.24 for moderate, <7.00 for severe)
• Serum bicarbonate: <15 mEq/L (15-18 for mild, 10-15 for moderate, <10 for severe)
• Ketones: Positive in both urine and serum
• Anion gap: ≥10 (typically ≥12 for moderate-severe)
• Effective serum osmolality: Variable

HHS Criteria 1, 2

• Plasma glucose: ≥600 mg/dL (≥30 mmol/L)
• Arterial pH: >7.30
• Serum bicarbonate: ≥15 mEq/L
• Ketones: Small or absent (≤3.0 mmol/L)
• Effective serum osmolality: ≥320 mOsm/kg (calculated as [2×Na+] + glucose + urea)
• Anion gap: Variable

Clinical Presentation Differences

Temporal Evolution 1

• DKA: Rapid onset, typically evolving within 24 hours
• HHS: Insidious onset, evolving over several days to weeks

This temporal difference is clinically crucial—patients presenting with acute hyperglycemic crisis over hours are more likely to have DKA, while those with gradual deterioration over days favor HHS.

Physical Examination Findings 1

DKA-specific findings:

• Kussmaul respirations (deep, rapid breathing to compensate for metabolic acidosis)
• Abdominal pain (present in DKA, typically absent in HHS)
• Vomiting (up to 25% of DKA patients, may be coffee-ground appearance)
• Fruity breath odor (from acetone)

HHS-specific findings:

• Profound alteration in mental status (more common and severe than DKA)
• Coma (occurs more frequently in HHS)
• Severe dehydration (fluid losses 100-220 mL/kg) 2
• Absence of Kussmaul respirations

Mortality Risk 1, 3

This distinction matters significantly for prognosis:

• DKA mortality: <1-5% in experienced centers
• HHS mortality: ~15% (approximately 10-fold higher than DKA)

The higher mortality in HHS is associated with extremes of age (>60 years), severity of dehydration, and presence of comorbidities 3.

Practical Diagnostic Algorithm

Step 1: Check plasma glucose

• If <250 mg/dL → Neither DKA nor HHS
• If 250-600 mg/dL → Consider DKA
• If ≥600 mg/dL → Consider HHS

Step 2: Assess acid-base status

• pH <7.30 and/or bicarbonate <15 mEq/L → DKA
• pH >7.30 and bicarbonate ≥15 mEq/L → HHS

Step 3: Check ketones

• Positive ketones → DKA
• Small or absent ketones → HHS

Step 4: Calculate effective osmolality

• ≥320 mOsm/kg → HHS
• <320 mOsm/kg → DKA (or less severe hyperglycemia)

Important Clinical Caveats

Mixed DKA/HHS 2, 4

Beware: Patients can present with overlapping features of both conditions. Mixed presentations are increasingly recognized, particularly in patients with type 2 diabetes who develop some degree of ketosis. These patients often have more severe metabolic derangements and higher rates of complications including acute kidney injury (84%) and electrolyte disturbances 4.

Common Pitfalls

1. Don't assume type 1 diabetes = DKA only: Type 2 diabetes patients can develop DKA, and increasingly younger adults are presenting with HHS 2

2. Don't rely on mental status alone: While altered mental status is more common in HHS, it can occur in both conditions and correlates with osmolality rather than being diagnostic 1

3. Don't miss the precipitant: Infection is the most common trigger for both conditions 1. Other precipitants include stroke, myocardial infarction, medications (corticosteroids, thiazides, sympathomimetics), and insulin non-compliance.

4. Hypothermia is a red flag: Despite infection being common, patients may be normothermic or hypothermic due to peripheral vasodilation. Hypothermia indicates poor prognosis 1

Misdiagnosis Consequences 5

A retrospective study found that HHS is commonly misdiagnosed as DKA, with only 5% of HHS patients correctly diagnosed initially. Of those misdiagnosed, 36% were readmitted within 2 weeks 5. This underscores the importance of calculating osmolality and checking ketones in all hyperglycemic emergencies.

Key Takeaway for Clinical Practice

The diagnostic triad that definitively separates HHS from DKA is: (1) osmolality ≥320 mOsm/kg, (2) minimal/absent ketones, and (3) pH >7.30 with bicarbonate ≥15 mEq/L. 1, 2 When these three criteria are met with glucose ≥600 mg/dL, the diagnosis is HHS. The presence of significant ketosis (positive ketones) and metabolic acidosis (pH <7.30, bicarbonate <15 mEq/L) with glucose ≥250 mg/dL confirms DKA.