DKA & HHS for FRCEM SBA: A Practical Guide for Emergency Medicine Doctors
What Are DKA & HHS and Why Do They Matter in the ED?
Diabetic ketoacidosis (DKA) is an acute, life-threatening complication of diabetes caused by absolute or relative insulin deficiency with excess counter-regulatory hormones. Clinically and biochemically it’s characterised by:
Hyperglycaemia
Ketonaemia/ketonuria
Metabolic acidosis (raised anion gap) (abcd.care)
The Joint British Diabetes Societies (JBDS) DKA guideline defines DKA in adults as: (abcd.care)
Capillary blood glucose >11 mmol/L (or known diabetes)
Capillary ketones >3 mmol/L (or urine ketones ≥ ++ )
Venous pH <7.3 and/or bicarbonate <15 mmol/L
Hyperosmolar hyperglycaemic state (HHS) is a severe hyperglycaemic emergency typically in older adults with type 2 diabetes, characterised by:
Marked hyperglycaemia (≥30 mmol/L)
High serum osmolality (≥320 mOsm/kg)
Severe dehydration
Minimal or no ketonaemia and no significant acidosis (pH ≥7.3, HCO₃⁻ ≥15 mmol/L) (abcd.care)
These are core ED emergencies with significant mortality, particularly HHS. For the FRCEM SBA, they’re classic “biochemistry-heavy” cases: lots of numbers, different criteria, fluid and insulin protocols, potassium pitfalls, and examination tricks like mixed DKA/HHS.
How DKA & HHS Appear in the FRCEM SBA Exam
You’ll see them pop up in multiple ways:
Diagnosis / recognition
Using biochemical criteria to distinguish DKA vs HHS vs simple hyperglycaemia.
Recognising mixed DKA/HHS (hyperosmolality with acidosis and ketonaemia). (Diabetes UK)
Initial investigation choice
Which blood tests to order (VBG/ABG, ketones, U&Es, osmolality).
Calculating effective osmolality and interpreting potassium.
First-line management
Fluid type and rate in DKA vs HHS.
Fixed-rate IV insulin infusion (FRIII) doses (0.1 vs 0.05 units/kg/hr). (abcd.care)
When to start dextrose, when to add potassium.
Complications / red flags
Cerebral oedema (especially in kids), arrhythmias, AKI, thromboembolism, mixed DKA/HHS.
Common question formats:
Biochemistry tables: glucose, ketones, pH, bicarbonate, Na⁺, osmolality.
Vignettes with FRIII + fluid protocol options, e.g. “what is the most appropriate next step?”.
Paeds vs adult DKA where the trick is “BSPED paeds fluid regime vs adult JBDS regime”. (bsped.org.uk)
Example mini-scenario:
A 27-year-old man with type 1 diabetes presents with vomiting and abdominal pain. Glucose 26 mmol/L, capillary ketones 5.4 mmol/L, venous pH 7.12, HCO₃⁻ 9 mmol/L, K⁺ 5.6 mmol/L. What is the most appropriate initial management step?
Core Concepts You Must Know About DKA & HHS
Definitions & Key Biochemical Criteria
Adult DKA – JBDS criteria (all three): (abcd.care)
Capillary blood glucose >11 mmol/L or known diabetes
Capillary ketones >3 mmol/L or urine ketones ≥ ++
Venous pH <7.3 and/or bicarbonate <15 mmol/L
Severity (useful for thinking, not rigidly tested):
Mild: pH 7.25–7.30, HCO₃⁻ 15–18
Moderate: pH 7.0–7.24, HCO₃⁻ 10–15
Severe: pH <7.0, HCO₃⁻ <10, or reduced GCS / shock
Adult HHS – JBDS criteria / characteristic features: (abcd.care)
Marked hypovolaemia
Serum osmolality ≥320 mOsm/kg
Calculate osmolality ≈ (2 × Na⁺) + glucose + urea (all in mmol/L)
Glucose ≥30 mmol/L
No significant ketonaemia (ketones ≤3 mmol/L)
No significant acidosis (pH ≥7.3, HCO₃⁻ ≥15 mmol/L)
Mixed DKA/HHS – treat as mixed picture if: (Diabetes UK)
Marked hypovolaemia
Osmolality ≥320 mOsm/kg
AND acidosis (pH <7.3, HCO₃⁻ <15)
AND significant ketonaemia (>3 mmol/L)
This mixed scenario is a favourite SBA twist.
Assessment & Investigations
Clinical clues
DKA: younger, type 1 diabetes, rapid onset over hours, polyuria, polydipsia, vomiting, abdominal pain, Kussmaul breathing, ketotic breath. (Patient)
HHS: older, type 2 diabetes, days–weeks of polyuria, polydipsia, weight loss, profound dehydration, confusion; no Kussmaul breathing, no obvious ketotic breath. (abcd.care)
Initial tests (both DKA & HHS):
Capillary glucose & ketones
VBG: pH, bicarbonate, lactate if needed
U&Es, creatinine, venous Na⁺/K⁺/Cl⁻
FBC, CRP, cultures as indicated (infection precipitant)
ECG (check for hyper-/hypokalaemia, MI)
Calculate corrected Na⁺ and osmolality
Biochemistry patterns:
DKA:
Glucose typically 13–30+ mmol/L (can be lower in “euglycaemic DKA”).
High anion gap metabolic acidosis.
Potassium high/normal on presentation but total body K⁺ depleted. (abcd.care)
HHS:
Glucose ≥30 mmol/L, sometimes 40–60+ mmol/L.
Serum osmolality ≥320 mOsm/kg.
pH ≥7.3, bicarbonate ≥15 (may have mild acidosis). (abcd.care)
Initial ED Management
Big picture:
Both conditions → treat ABCDE, restore volume, correct biochemistry, treat precipitant, but the tempo and aggressiveness differ:
DKA: faster fluids + fixed-rate insulin aimed at ketone clearance and acidosis resolution. (abcd.care)
HHS: slower, gentler correction to avoid rapid shifts in osmolality (risk of cerebral oedema, osmotic demyelination). (abcd.care)
Adult DKA – JBDS-style approach (simplified): (abcd.care)
Fluids first
0.9% NaCl bolus (e.g. 500–1000 mL over first hour) unless heart failure.
Continue 0.9% NaCl guided by BP, HR, urine output, and local protocol.
Fixed-rate IV insulin infusion (FRIII)
Start 0.1 units/kg/hr after first litre of fluid (unless significant hypokalaemia).
Aim for ketone fall ~0.5 mmol/L/hr and glucose fall ≥3 mmol/L/hr.
Potassium management
K⁺ >5.5 → no K⁺ in first bag, monitor closely.
3.5–5.5 → add K⁺ (e.g. 40 mmol/L) to fluids as per local protocol.
<3.5 → delay insulin, start K⁺ replacement and get senior help.
When glucose <14 mmol/L
Add 10% dextrose (e.g. 125 mL/hr) alongside 0.9% NaCl and continue FRIII to clear ketones.
Resolution of DKA (biochemical)
Ketones <0.6 mmol/L, pH >7.3, HCO₃⁻ ≥18 mmol/L. (mkuh.nhs.uk)
Adult HHS – JBDS-style approach (simplified): (abcd.care)
Fluids – very cautious, very important
0.9% NaCl is mainstay. Replace slowly over 24 hours, targeting gradual osmolality reduction (≤10 mOsm/kg/hr) and glucose fall (~3–6 mmol/L/hr).
Avoid rapid sodium shifts, especially in elderly/CKD.
Insulin is secondary, and delayed
Initial focus: fluids alone.
When glucose plateaus or if significant ketonaemia present:
Pure HHS (ketones <3 mmol/L, pH ≥7.3) → low-dose FRIII 0.05 units/kg/hr.
Mixed DKA/HHS (ketones >3 and pH <7.3) → treat as DKA with FRIII 0.1 units/kg/hr.
Potassium & VTE prophylaxis
Same principles as DKA: total body K⁺ depleted, so monitor closely.
HHS is highly pro-thrombotic; LMWH prophylaxis is usually recommended unless contraindicated.
Trigger management
Infection, MI, stroke, drugs (steroids, SGLT2 inhibitors for DKA risk) – identify and treat.
Red Flags and Pitfalls
Red flags:
DKA: Kussmaul breathing, hypotension/shock, reduced GCS, severe acidosis (pH <7.0), hyperkalaemia on ECG.
HHS: Marked confusion, seizures, focal neurology (stroke), osmolality >350, Na⁺ >160 mmol/L. (abcd.care)
Common pitfalls (very FRCEM-ish):
Treating HHS like DKA (aggressive insulin + fast fluids) → rapid osmolality drop and neurological injury.
Starting insulin in DKA before replacing potassium when K⁺ is low.
Stopping insulin just because the glucose normalised – the target is ketone clearance and acidosis resolution, not glucose alone. (abcd.care)
Forgetting to continue basal insulin (if the patient was on long-acting insulin pre-admission).
Special Populations
Children & young people (paediatric DKA)
Use BSPED DKA guideline (vs adult JBDS): slower fluid replacement and more conservative correction due to cerebral oedema risk. (bsped.org.uk)
Large fluid boluses generally avoided unless shocked.
FRCEM SBA may test “pick the paediatric-appropriate fluid strategy”.
Older frail adults (especially in HHS)
High risk of fluid overload and AKI – careful balancing act.
May have mixed HHS/DKA; treat cautiously with senior support.
Pregnancy
DKA can develop at lower glucose levels; foetal monitoring and urgent obstetric involvement.
Common FRCEM SBA Traps Related to DKA & HHS
“Question writers love to test the difference between X and Y…”
DKA vs HHS vs mixed picture
Trap: Labeling an older patient with glucose 40, osmolality 340, pH 7.10, ketones 5 mmol/L as “HHS”.
Fix: That’s a mixed DKA/HHS – treat with DKA protocol but mindful of hyperosmolality.
Hyperglycaemia without acidosis
Trap: Starting DKA protocol for glucose 28 mmol/L but ketones 0.4, pH 7.39, HCO₃⁻ 25.
Fix: This is uncomplicated hyperglycaemia, not DKA or HHS – manage underlying cause, not FRIII.
Stopping insulin too early
Trap: Turning off FRIII once glucose hits 10–12 mmol/L.
Fix: Add dextrose and continue insulin until ketones and acidosis resolve.
Over-aggressive correction in HHS
Trap: DKA-style fast fluids and insulin in pure HHS.
Fix: In HHS, focus on slow fluid resuscitation first, insulin later, to avoid rapid osmolality shifts. (abcd.care)
Ignoring potassium
Trap: Starting insulin with K⁺ 2.8 mmol/L.
Fix: Replace K⁺ and involve senior/critical care; insulin will further drop serum K⁺.
High-Yield Clinical Patterns for DKA & HHS in the ED
Classic Presentation – Adult DKA
Age: 23-year-old man with type 1 diabetesSymptoms: 24 hours of vomiting, polyuria, polydipsia, abdominal painObs: HR 120, BP 96/60, RR 28 with deep sighing breaths, SpO₂ 98% RA, T 37.8°CLabs: Glucose 26 mmol/L, ketones 6.0 mmol/L, pH 7.09, HCO₃⁻ 8 mmol/L, K⁺ 5.4 mmol/L
Pattern:
Young, type 1, rapid onset, Kussmaul breathing, marked acidosis, high ketones → textbook DKA.
Classic Presentation – HHS
Age: 78-year-old woman with type 2 diabetesSymptoms: 1–2 weeks of thirst, polyuria, lethargy, now confusedObs: HR 105, BP 100/60, RR 20, SpO₂ 96% RA, GCS 13Labs: Glucose 42 mmol/L, Na⁺ 152 mmol/L, urea 18 mmol/L, pH 7.36, HCO₃⁻ 22 mmol/L, ketones 0.8 mmol/LCalculated osmolality: (2 × 152) + 42 + 18 ≈ 364 mOsm/kg
Pattern:
Elderly, type 2, insidious course, severe dehydration, very high osmolality, minimal ketones, no acidosis → pure HHS.
Dangerous Mimics
Differentials you must consider:
Lactic acidosis from sepsis or shock – high lactate, variable glucose, no ketonaemia.
Alcoholic ketoacidosis – history of binge drinking, normal/low glucose, high ketones, metabolic acidosis.
Starvation ketosis – mild ketonaemia, limited acidosis.
Salicylate toxicity – mixed respiratory alkalosis and metabolic acidosis.
In the exam, “ketones high + glucose high + anion gap acidosis” is usually DKA until proven otherwise; they love to use biochemistry to separate these.
How to Revise DKA & HHS Efficiently for the FRCEM SBA
Use Question Banks First, Then Guidelines
Do blocks of DKA/HHS SBAs:
Focus on criteria, fluid regimes, insulin rates, potassium plans, mixed DKA/HHS.
Then read the key guideline chunks:
JBDS 02 – Management of DKA in Adults (2023). (abcd.care)
JBDS 06 – Management of HHS in Adults. (abcd.care)
BNF/BNFC “Diabetic hyperglycaemic emergencies” summaries (good for pharmacology, insulin/dextrose/K⁺). (BNF)
BSPED DKA guideline for paeds. (bsped.org.uk)
RCEMLearning DKA and HHS modules for EM-specific nuance. (rcemlearning.co.uk)
This keeps your numbers and sequences current and UK-aligned.
Build Mini-Notes or Flashcards from Mistakes
Every time you miss a DKA/HHS question, jot:
What the question really tested:
“Differentiate DKA vs HHS vs mixed.”
“When to start insulin in HHS.”
“Biochemical criteria for DKA resolution.”
Why you were wrong:
“I used glucose alone, ignored ketones/pH.”
“I treated high osmolality like DKA.”
One-liner rule:
“DKA = high ketones + metabolic acidosis; HHS = high osmolality + severe hyperglycaemia with minimal ketones and no acidosis.”
“In HHS, fluids first; insulin later and gentler.”
These are ideal high-yield flashcards for final-week review.
Mix Text-Based and Image/Data-Based Questions
Practise data-heavy SBAs: tables of glucose/ketones/pH/HCO₃⁻/Na⁺/osmolality where you must pick diagnosis + next step.
Use flow-diagram SBAs that mimic DKA/HHS pathways (fluid + insulin + K⁺).
Add ECG-based questions for potassium (peaked T waves, broad QRS, etc.).
How StudyMedical Covers DKA & HHS in Its FRCEM SBA Question Bank
Within StudyMedical’s FRCEM SBA bank, DKA and HHS questions can be mapped cleanly to the RCEM 2021 curriculum endocrine section and updated UK guidance:
Curriculum-mapped DKA and HHS vignettes
From straightforward young type 1 DKA to frail elderly HHS and nasty mixed cases, all with full vitals and biochemistry.
Biochemistry-heavy SBAs
Serial labs showing ketone clearance, pH and bicarbonate changes, evolving osmolality, potassium shifts – exactly the style examiners use to see if you truly understand the numbers.
Image-/data-based SBAs where relevant
ECGs for potassium, CXR for aspiration/infection, charts of fluid and insulin rates to interpret.
Detailed explanations referencing JBDS / BNF / RCEM resources
So every question doubles as a concise explanation of why that particular fluid/insulin/K⁺ plan is correct within UK pathways.
FAQs About DKA & HHS in the FRCEM SBA
How often do DKA and HHS appear in the FRCEM SBA exam?
Very regularly. They sit at the crossroads of endocrine, resus and acute medicine, and they’re perfect for biochemistry-heavy, protocol-based questions.
What’s the single most important thing to remember about DKA vs HHS for the exam?
DKA = ketones + acidosis; HHS = hyperosmolality + severe hyperglycaemia with little/no ketones and no significant acidosis. That simple mental fork will get you through many stems.
Are there must-know guidelines for DKA and HHS?
Yes:
JBDS 02 – Management of DKA in Adults. (abcd.care)
JBDS 06 – Management of HHS in Adults. (abcd.care)
BSPED DKA Guideline for paediatrics. (bsped.org.uk)
BNF/BNFC summaries on diabetic hyperglycaemic emergencies. (BNF)
How many DKA/HHS-related questions should I aim to do before the exam?
Aim for at least 30–40 focused DKA/HHS SBAs, plus lots of mixed endocrine/resus questions, until the criteria, fluid plans, insulin rates and K⁺ rules feel automatic.
Key Takeaways: DKA & HHS for FRCEM in 5 Bullet Points
DKA: glucose >11, ketones >3, pH <7.3 and/or HCO₃⁻ <15 – think ketones + acidosis. (abcd.care)
HHS: glucose ≥30, osmolality ≥320, severe dehydration, minimal ketones, no significant acidosis – hyperosmolar, not ketoacidotic. (abcd.care)
DKA management: fluids → FRIII 0.1 units/kg/hr → add dextrose when glucose <14 → keep insulin going until ketones and acidosis resolve. (abcd.care)
HHS management: slower fluids, careful osmolality change, insulin delayed/low-dose (0.05 units/kg/hr) and only once volume status improved or glucose plateaus. (abcd.care)
Potassium can kill your patient and your SBA score – always know where it is, replace appropriately, and never start insulin in a profoundly hypokalaemic patient.
Ready to Test Yourself on DKA & HHS?
DKA and HHS are high-yield, biochemistry-heavy topics that FRCEM examiners love:
They test your ability to interpret numbers, follow UK protocols, and avoid dangerous pitfalls in real practice.
Once you’ve seen enough SBAs, the patterns (and the maths) become much easier.
