DKA vs HHS: How the NCLEX Tells Them Apart

Medical-Surgical · Endocrine (Diabetes, Thyroid)·Updated 2026-10-28

What it is

Both are hyperglycemic emergencies caused by too little insulin action plus a stressor such as infection or missed insulin. In diabetic ketoacidosis (DKA), the near-absence of insulin forces fat breakdown, ketone production and metabolic acidosis within hours, usually in type 1 diabetes. In hyperosmolar hyperglycemic state (HHS), enough insulin remains to prevent ketosis, so glucose climbs over days and causes extreme osmotic diuresis, dehydration and hyperosmolality, usually in older adults with type 2 diabetes. In both, fluid replacement comes first, then insulin, with potassium watched closely.

What the NCLEX focuses on

DKA: Kussmaul respirations, fruity (acetone) breath, abdominal pain, nausea and vomiting, and dehydration.
HHS: extreme hyperglycemia, profound dehydration and neurologic changes (confusion, seizures, coma) without significant ketosis or acidosis.
The arterial blood gas in DKA shows metabolic acidosis with respiratory compensation: low pH, low bicarbonate and low PaCO2.
Fluids come first: IV 0.9% sodium chloride restores volume and lowers glucose on its own.
IV regular insulin is given by continuous infusion only after potassium is known to be at least 3.5 mEq/L, because insulin drives potassium into cells.
Serum potassium is often normal or high at presentation despite total-body depletion, then falls during treatment; replace it with cardiac monitoring.
In DKA, dextrose is added when glucose falls to about 250 mg/dL, and the insulin infusion continues until the anion gap closes; subcutaneous basal insulin overlaps the infusion by 1 to 2 hours.

Priority nursing actions

Assess the airway and level of consciousness and establish IV access.
Infuse the prescribed 0.9% sodium chloride rapidly to restore circulating volume.
Check serum potassium before insulin; replace potassium first if it is below 3.5 mEq/L.
Start the prescribed IV regular insulin infusion and check glucose hourly.
Monitor cardiac rhythm, potassium, intake and output, neurologic status and acid-base results.
Treat the trigger, often infection or missed insulin, and give subcutaneous insulin before the infusion is stopped.

Numbers to know

Value	DKA	HHS
Blood glucose	250 mg/dL (13.9 mmol/L) or higher	Often above 600 mg/dL (33.3 mmol/L)
Arterial pH	Below 7.30	Above 7.30
Serum bicarbonate	Below 18 mEq/L (18 mmol/L)	Above 18 mEq/L (18 mmol/L)
Ketones	Moderate to large in blood and urine	Absent or minimal
Serum osmolality	Variable	Above 320 mOsm/kg (320 mmol/kg)
Onset and typical client	Hours; type 1 diabetes	Days; older adult with type 2 diabetes
Potassium before insulin	At least 3.5 mEq/L (3.5 mmol/L)	At least 3.5 mEq/L (3.5 mmol/L)

Common exam traps

Choosing to start the insulin infusion before fluids or a potassium result: wrong because insulin drops serum potassium and dysrhythmias follow.
Choosing to withhold potassium because the first serum level is normal: wrong because total-body potassium is depleted and the level falls once insulin starts.
Choosing to stop the insulin infusion when glucose reaches 250 mg/dL: wrong because insulin is still needed to clear ketones; dextrose is added instead.
Choosing routine sodium bicarbonate: wrong because fluids and insulin correct the acidosis; bicarbonate is reserved for severe acidosis.
Choosing Kussmaul respirations and fruity breath as signs of HHS: wrong because HHS has little or no ketosis or acidosis.

What to teach

Sick days: never stop insulin when ill; check glucose every 3 to 4 hours and test for ketones when glucose is above 240 mg/dL.
Sip fluids every hour, and use carbohydrate-containing liquids if solid food is not tolerated.
Call the provider for persistent vomiting or diarrhea, moderate or large ketones, or glucose that stays high despite correction insulin.
Older adults with type 2 diabetes: drink fluids regularly and report increasing thirst, frequent urination or confusion.

Client handout: Low Blood Sugar (Hypoglycemia) and Sick-Day Rules (nurse guide and printable patient handout).

Try 2 NCLEX-style questions on this topic

From the NCLEXPace question bank. Pick your answers, then check them inside NCLEXPace.

Question 1 · QID 07510DF6

A client with type 1 diabetes has glucose 512 mg/dL, moderate urine ketones, and deep rapid respirations. Which arterial blood gas result should the nurse expect?

Select the best answer.

A. pH 7.28, PaCO2 52 mm Hg, bicarbonate 24 mEq/L
B. pH 7.28, PaCO2 26 mm Hg, bicarbonate 12 mEq/L
C. pH 7.50, PaCO2 46 mm Hg, bicarbonate 35 mEq/L
D. pH 7.50, PaCO2 28 mm Hg, bicarbonate 22 mEq/L

Question 2 · QID C6FA30C1

The emergency department nurse compares two clients with severe hyperglycemia. For each finding, select the condition it best supports.

For each finding, select the condition it best supports. Each row has one answer.

	Diabetic ketoacidosis (DKA)	Hyperosmolar hyperglycemic state (HHS)
Deep, rapid Kussmaul respirations with fruity breath odor
Glucose 720 mg/dL with absent-to-minimal serum ketones
Gradual onset over days in an older adult with type 2 diabetes
Abdominal pain with nausea and vomiting at presentation
Profound dehydration with progressing neurologic changes
Arterial pH 7.12 with bicarbonate 10 mEq/L

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Sources

Harding MM, Kwong J, Hagler D, Reinisch C. Lewis's Medical-Surgical Nursing: Assessment and Management of Clinical Problems. 12th ed. Elsevier; 2023; Chapter: Diabetes.
Kitabchi AE, Umpierrez GE, Miles JM, Fisher JN. Hyperglycemic crises in adult patients with diabetes. Diabetes Care. 2009;32(7):1335-1343.
Umpierrez GE, Davis GM, ElSayed NA, et al. Hyperglycemic Crises in Adults With Diabetes: A Consensus Report. Diabetes Care. 2024;47(8):1257-1275.

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