Reasoning GP · Algorithm · 1-page summary
Hypokalaemia in adults
For: adults with a potassium result below 3.5 mmol/L in primary care. Not for: children; DKA; hospital IV replacement (full algorithm, step 7); eating-disorder care (eating disorders protocol).
Core rule: K⁺ <2.5 mmol/L or a significant ECG abnormality needs urgent hospital assessment for monitored replacement — 999 if unstable. A normal ECG does not exclude important hypokalaemia. Check magnesium every time: potassium may stay low until it is corrected.
0Stop — emergency hospital assessment — 999 if unstable; do not delay transfer for outpatient investigations
- K⁺ <2.5 mmol/L → Same-day hospital, usually admission. Unstable, arrhythmia, paralysis, respiratory compromise, syncope, chest pain or collapse → 999
- Significant ECG abnormality (arrhythmia, frequent ventricular ectopy, marked ST/T change, prominent U waves; wide QRS is late) → urgent monitored replacement; arrhythmia or unstable → 999
- Ascending weakness, unable to walk, respiratory muscle weakness → 999. Rhabdomyolysis (muscle pain, dark urine, AKI) → emergency hospital assessment, 999 if unstable.
- On digoxin with toxicity features (palpitations, bradycardia, heart block, syncope, confusion, vomiting, visual disturbance) → ECG; discuss with acute medicine/toxicology now; 999 if unstable. Never IV potassium in primary care.
1Triage by level — <2.5 is block 0
| K⁺ mmol/L | Action |
|---|---|
| 2.5–2.9 | ECG and clinical assessment → Same-day. Oral only if well, absorbing, no significant ECG change, reliable follow-up. Symptomatic, vomiting, dehydrated, digoxin, cardiac disease, renal impairment or falling → Same-day hospital |
| 3.0–3.4 | Usually asymptomatic → primary care: treat the cause, review the diuretic; recheck U&E and magnesium within about 1 week. |
2Screen — one row is enough
- Palpitations, severe weakness, cramps → Same-day assessment and ECG. Chest pain, syncope, collapse → 999
- Vomiting or diarrhoea, cannot take oral, postural drop → Same-day medical (IV fluids).
- Suspected purging (normal BP, alkalosis, no diuretic prescribed): ask directly. MEED: K⁺ <2.5 (red), bradycardia, postural drop or rapid weight loss → Same-day medical assessment; refer eating-disorder service (NG69).
- Severe alkalosis, rapid-onset hypertension, proximal weakness, hyperglycaemia (smoker): ectopic ACTH → Same-day endocrine advice; 40+ meeting NG12 → Chest X-ray ≤2 weeks
3Assess — once blocks 0–2 are answered
☐ BP, postural BP, pulse and rhythm, weight; power, reflexes, bowel sounds ☐ ECG if symptomatic, K⁺ <3.0, digoxin or anti-arrhythmics, significant cardiac disease ☐ Repeat U&E with magnesium, bicarbonate, glucose; venous gas if unwell; urine K⁺ only if cause unclear
Not in primary care: IV potassium; a 9 am cortisol to screen for Cushing's.
4Classify the mechanism — once urgency is settled
- Renal loss — diuretics (commonest); Conn's or Cushing's (hypertension, alkalosis); RTA (acidosis); Bartter/Gitelman; low magnesium.
- GI loss — vomiting (alkalosis), diarrhoea, laxatives, high-output stoma → treat the cause.
- Shift — insulin, beta-agonists, alkalosis, refeeding, periodic paralysis → treat the driver; cautious K⁺ (rebound).
- Intake — rare alone. Uncertain or recurrent — investigate; block 6.
5Treat today — mild, or moderate and well
- Oral potassium chloride (Sando-K 12 mmol/tablet), dissolved, with or after food. SPS typical: mild 24 mmol two or three times daily; moderate 24–36 mmol three or four times daily. Lower in CKD. Doses: NICE/SPC, BNF, local formulary.
- Magnesium: correct significant hypomagnesaemia at the same time (formulary/SPC); hospital advice if severe, symptomatic, IV or renal impairment.
- Drugs: reduce the diuretic, or discuss a potassium-sparing strategy with a specialist; endocrine advice first if Conn's suspected. Stop laxatives, liquorice.
- Recheck U&E and magnesium: mild within about 1 week; moderate 24–72 h. Not rising → check magnesium, adherence, losses before increasing.
6Refer routinely
- Hypertension with hypokalaemia → aldosterone:renin ratio (K⁺ corrected, lab protocol on medicines) → endocrinology if raised.
- Cushingoid features, or persistent hypokalaemia off diuretics → endocrinology. Acidosis with normal anion gap (RTA), or young, normotensive with low magnesium (Bartter/Gitelman) → nephrology.
- Refractory despite K⁺, magnesium and diuretic change → endocrinology or nephrology.
7Never reassure by — never manage K⁺ <2.5 in the community
- The patient feeling well, or a normal ECG.
- "It's the diuretic" without the magnesium, bicarbonate and BP.
- "Refractory" before the magnesium is checked and corrected.
- A diuretic explanation in a young normotensive patient — ask about purging.
- Salt substitutes or diet alone as treatment for ongoing losses.
8Safety-net — say it, then document it
999 “Call 999 for chest pain, fainting or collapse, palpitations with feeling faint or breathless, severe weakness or being unable to walk, difficulty breathing, new confusion, or dark urine with severe muscle pain.”
Same day: “Contact us today if cramps or weakness get worse despite the tablets, you have palpitations, vomiting or diarrhoea stops you taking them, or a new medicine is started.” Remote: K⁺ 2.5–2.9 needs an ECG and assessment the same day.
✓Safe to manage in primary care only if — all five, documented
No block 0–2 row; K⁺ 3.0–3.4, or 2.5–2.9 meeting oral criteria
ECG done where indicated and normal
Magnesium, bicarbonate, BP checked
Cause acted on; recheck booked (1 week / 24–72 h)
Safety-net given
Summary of the full Reasoning GP hypokalaemia algorithm, which holds the detail, hospital IV replacement and evidence. Sources: NHS SPS Treating acute hypokalaemia in adults (2024); NICE NG136, NG69, CG32, CG174, NG12; RCPsych CR233 (MEED); local formulary; SPCs. Clinical reference — follow local acute-transfer, renal and prescribing policies and check doses: NICE/SPC, BNF.