Nephrology
Potassium disorders
Written 30 September 2026. This date is not a physician-review date.
Why this matters
Potassium kills by changing the cardiac membrane, and the serum number is not the whole story.
Rapid clinical summary
- Hyperkalemia with ECG changes is a membrane emergency.
- Calcium stabilizes the membrane. It does not remove potassium.
- Hypokalemia is weakness and arrhythmia risk. Do not give insulin to a low potassium.
Mechanism
Potassium sets the resting membrane potential. A high level slows conduction: peaked T waves, a widening QRS, then a sine-wave pattern. A low level increases excitability and can prolong the QT interval or cause weakness.
Recognition
Look at the ECG when the history could raise potassium. Do not wait for a repeat laboratory result if the monitor is already changing.
Typical
- Weakness
- A missed dialysis session
- An ACE inhibitor plus a potassium-sparing drug
- Diarrhea or diuretics for a low level
Red flags
- Peaked T waves
- Wide QRS
- Loss of P waves
- A sine-wave ECG
- Paralysis
Differential
| Condition | Clue | Trap |
|---|---|---|
| Hemolysis of the sample | An unexpected number and a normal ECG | Treating a spurious result as if the heart were failing |
| Acidosis shifting potassium | The total body store may not be high | Forgetting that treatment of the acid can drop the serum level |
| Magnesium depletion with hypokalemia | Potassium will not stay corrected | Repeating potassium replacement alone |
Investigations
- ECG.
- Repeat potassium if the result does not fit a well patient, but do not delay membrane protection when the ECG is already toxic.
- Renal function, and a review of drugs.
Management
- Immediate
- If the ECG shows toxicity, give calcium to stabilize the membrane, then shift potassium, then remove it. Doses are not stated.
- Definitive
- Stop the cause. Dialysis if the kidneys cannot clear potassium and the level or ECG demands it. For hypokalemia, replace potassium and the reason it was lost.
- Monitoring
- Continuous cardiac monitoring when the ECG is abnormal. Recheck the level after shifts, because a temporary move into cells is not removal.
Common pitfalls
- Using a resin as the only step for a wide QRS.
- Giving potassium to a hyperkalemic patient.
- Treating a hemolyzed sample in a well person with the full emergency sequence.
Exam reasoning
The question is sequence. Membrane first when the ECG is toxic. Removal is the next problem.
Practice this topicOpens original Mahazanaka questions in this subject. If this subject is thin on that track, the session uses what exists.
Visual summary
Calcium is not a potassium-lowering drug.
Recognize, reason, prioritize, act safely
- Recognize. The ECG, not only the number.
- Reason. Is this membrane toxicity, a shift, or a false sample?
- Prioritize. Protect the heart before you lower the number.
- Act safely. Calcium for toxicity, then shift, then remove. No dose on this page.
Knowledge check
Missed dialysis, weakness, peaked T waves, widening QRS. What is the immediate priority?
No citation is attached to this chapter. Nothing here is personal medical advice.