DKA vs HHS for MRCP Part 1
- Crack Medicine
- Apr 30
- 2 min read
TL;DR
Endo: Diabetic Emergencies: DKA vs. HHS is a core MRCP Part 1 topic testing rapid differentiation and safe management. DKA features ketosis and acidosis, whereas HHS presents with severe hyperglycaemia and hyperosmolality without significant ketosis. Initial management prioritises fluids, potassium correction, and controlled insulin therapy. Recognising key differences prevents complications such as cerebral oedema (DKA) and thrombotic events (HHS).
Why this matters
In MRCP Part 1, diabetic emergencies are consistently tested because they integrate physiology, clinical reasoning, and acute management. Candidates must distinguish DKA from HHS, interpret laboratory findings accurately, and apply guideline-based treatment safely.
For a broader overview, visit the MRCP Part 1 overview. Practise exam-style questions with Free MRCP MCQs or simulate exam conditions via Start a mock test.
Core sections
1) Definitions and diagnostic thresholds
DKA (Diabetic Ketoacidosis)
Glucose: >11 mmol/L
Ketones: ≥3.0 mmol/L (blood)
pH: <7.30
Bicarbonate: <15 mmol/L
HHS (Hyperosmolar Hyperglycaemic State)
Glucose: >30 mmol/L
Osmolality: ≥320 mOsm/kg
Ketones: minimal/absent
pH: >7.30
2) Pathophysiology
DKA: Absolute insulin deficiency → lipolysis → ketone production → metabolic acidosis
HHS: Relative insulin deficiency → hyperglycaemia → osmotic diuresis → dehydration without ketosis
3) Precipitating factors
Infection (most common)
Missed insulin
Myocardial infarction or stroke
Drugs (steroids, SGLT2 inhibitors)
Undiagnosed diabetes
4) Clinical features
DKA: Rapid onset, abdominal pain, vomiting, Kussmaul respiration
HHS: Gradual onset, severe dehydration, neurological deficits
5) Key comparison table
Feature | DKA | HHS |
Onset | Rapid | Gradual |
Glucose | Moderate ↑ | Very high |
Ketones | High | Low |
pH | Low | Normal |
Osmolality | Mild ↑ | Marked ↑ |
Mortality | Lower | Higher |
6) Investigations
Blood glucose and ketones
ABG/VBG
Electrolytes (especially potassium)
Serum osmolality
ECG and infection screen
7) Management (exam-focused steps)
Step 1: Fluids
0.9% saline initially
Step 2: Potassium correction
Delay insulin if K⁺ <3.5 mmol/L
Step 3: Insulin therapy
Fixed-rate IV insulin (DKA)
Delayed/low-dose insulin (HHS)
Step 4: Add dextrose
When glucose <14 mmol/L
Step 5: Monitor closely
Hourly glucose, ketones, electrolytes
8) Five most tested subtopics
Ketone metabolism
Osmolality calculation
Potassium management
Insulin protocols
Complications
9) Five traps
Starting insulin before correcting potassium
Ignoring euglycaemic DKA
Misinterpreting ketone results
Rapid correction of osmolality
Missing thromboprophylaxis in HHS
Practical examples / mini-cases
Case: A 30-year-old presents with vomiting and confusion. Labs show glucose 20 mmol/L, ketones 5 mmol/L, pH 7.1, K⁺ 3.3 mmol/L.
Answer: Correct potassium before insulin.
Explanation: Hypokalaemia must be corrected first to prevent arrhythmias. Insulin therapy is delayed until potassium is safe.
Common pitfalls (5 bullets)
Early insulin without fluids
Inadequate potassium monitoring
Failure to add glucose infusion
Misclassification of HHS
Ignoring complications
FAQs
1) What is the main difference between DKA and HHS?
DKA involves ketosis and acidosis; HHS involves severe hyperglycaemia and hyperosmolality without ketosis.
2) Why is potassium important?
Total body potassium is depleted even if serum levels appear normal.
3) When is insulin started?
After fluids and potassium correction in DKA; delayed in HHS.
4) What complications are important?
Cerebral oedema (DKA) and thrombosis (HHS).
5) Can DKA occur with normal glucose?
Yes, especially with SGLT2 inhibitors (euglycaemic DKA).
Ready to start?
Reinforce your understanding with targeted practice using Free MRCP MCQs and test readiness with Start a mock test. For structured revision, revisit the MRCP Part 1 overview.
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