DKA vs HHS vs Hypoglycemia: Triage of Diabetic Emergencies
Renal & Endocrine · 7 min read · Published 2026-09-14
Introduction
A patient with diabetes presents obtunded with glucose of 900 mg/dL. Is it DKA, HHS, or something else? The three diabetic emergencies share a cast of high or low glucose, altered mental status, and metabolic derangement, but their mechanisms - and their treatments - diverge sharply. Step 1 tests the biochemistry; Step 2 CK tests the triage.
DKA: The Ketone-Driven Emergency
DKA is absolute or near-absolute insulin deficiency, classically in type 1 diabetics, often precipitated by infection, missed insulin, or new-onset disease. Without insulin, cells cannot take up glucose, so the body burns fat wholesale. The result is a triad:
- Hyperglycemia (usually > 250 mg/dL)
- Ketosis (acetoacetate and beta-hydroxybutyrate) with a high anion-gap metabolic acidosis
- Kussmaul respirations blowing off CO2 as compensation, plus acetone on the breath
Volume depletion comes from osmotic diuresis - patients are typically 3-6 liters down. Potassium is the classic trap: serum K may be normal or high from acidosis-driven extracellular shift, but total-body K is severely depleted. Potassium below 3.3 mEq/L means you must replace it before insulin, or insulin will drive K into cells and precipitate fatal hypokalemia.
HHS: The Osmolality-Driven Emergency
Hyperosmolar hyperglycemic state is the type 2 counterpart: enough residual insulin to prevent ketogenesis, but not enough to prevent weeks of rising glucose. The signature:
- Profound hyperglycemia (often > 600 mg/dL)
- No significant ketosis, so pH and bicarbonate are near-normal
- Markedly elevated serum osmolality (> 320 mOsm/kg) driving severe dehydration and obtusion - mental status correlates with osmolality, not glucose
HHS carries a higher mortality than DKA precisely because patients are older, more volume-depleted (often 9 liters down), and present later.
Hypoglycemia: The Wrong-Direction Emergency
Glucose below 70 mg/dL with adrenergic symptoms (tremor, sweating, anxiety) progresses below 55 to neuroglycopenic symptoms (confusion, seizure, coma). The diagnostic workup in a non-diabetic patient is the critical part - draw glucose, insulin, C-peptide, and sulfonylurea screen during the hypoglycemic episode:
| Finding | Exogenous insulin | Sulfonylurea | Insulinoma |
|---|---|---|---|
| Insulin | High | High | High |
| C-peptide | Low | High | High |
| Sulfonylurea screen | Negative | Positive | Negative |
The C-peptide split is the test's favorite discriminator: exogenous insulin suppresses C-peptide, while anything driving endogenous secretion raises it.
The Comparison Table
| Feature | DKA | HHS | Hypoglycemia |
|---|---|---|---|
| Typical patient | Type 1 | Type 2, elderly | Any |
| Glucose | > 250 | > 600 | < 70 |
| Ketones / anion gap | Present / high | Absent / normal | Normal |
| pH | Low | Normal | Normal |
| Osmolality | Mildly high | Very high | Normal |
| Mental status | Variable | Markedly obtunded | Confusion → coma |
| Onset | Hours to days | Days to weeks | Minutes |
Treatment Priorities
Both DKA and HHS share the same resuscitation backbone: fluids first (aggressive isotonic saline), then potassium check, then insulin infusion - in that order. Bicarbonate is reserved only for pH below 6.9. The resolution endpoint for DKA is gap closure, not glucose normalization, so transition to subcutaneous insulin only after the anion gap closes and the patient eats. In hypoglycemia, treatment is immediate dextrose (or glucagon if no IV access), with the diagnostic labs drawn before correction in non-diabetics.
Common Pitfalls
- Giving insulin to a DKA patient with K < 3.3 before replacing potassium
- Chasing glucose instead of osmolality in HHS - mental status follows osmolality
- Expecting ketones in HHS; their absence is the point
- Forgetting to draw insulin, C-peptide, and sulfonylurea levels before giving dextrose in unexplained hypoglycemia
- Stopping the DKA insulin infusion the moment glucose normalizes, before the gap closes
Clinical Pearl
When a vignette gives you glucose over 600 with pH 7.38 and bicarbonate 22, it is handing you HHS - the normal pH is the tell. When it gives you glucose of 300 with pH 7.1 and a gap of 22, that is DKA, and the glucose number matters far less than the gap. Read the acid-base first, the glucose second.
Summary
DKA is a ketone and pH problem, HHS is an osmolality and volume problem, and hypoglycemia is a diagnosis problem in non-diabetics and a treatment problem in diabetics. Fluids, potassium, insulin - in that order - covers the first two, and C-peptide separates the causes of the third. These patterns are heavily tested because they test reasoning under time pressure, exactly what our clinical case library is built to train.