Nursing care
High potassium on a haemolysed sample: assess the client before treating
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
A high potassium on a haemolysed sample may be falsely raised, because damaged red cells release potassium into the specimen. The nurse assesses the client, checks the ECG and risk factors, and reports both the result and the haemolysis to the provider. A redraw is usually needed, but ECG changes or high-risk findings mean treating it as real while confirming.
Why haemolysis raises the measured potassium
Most of the body's potassium sits inside cells. When red blood cells break during or after collection, that potassium spills into the plasma or serum in the tube, so the laboratory measures a higher value than is present in the client's blood. This is called pseudohyperkalaemia, and in vitro haemolysis is its most common cause.
Collection technique contributes. Repeated fist clenching, a prolonged tourniquet, forceful transfer through a small needle, vigorous shaking and delayed processing can all damage cells or shift potassium out of them. Very high platelet or white cell counts can also falsely raise potassium. Many analysers report a haemolysis index, which flags affected specimens more reliably than visual inspection.
The first action: assess the client and the ECG
Before acting on the number, assess the client. Check the cardiac monitor or obtain an ECG as ordered, looking for peaked T waves, widened QRS or new arrhythmia. Ask about muscle weakness, numbness or palpitations, and review risk factors such as kidney injury, potassium supplements, potassium-sparing medicines and tissue breakdown.
Then notify the provider, reporting the value, the haemolysis comment and your assessment together. A safety case review described a client whose haemolysed result was treated aggressively despite an ECG suggesting low potassium; the treatment caused dangerous hypokalaemia and a fatal arrhythmia. Correlating the result with the client is the step that prevents that harm.
Redraw or treat now: weighing the evidence
If the client has no ECG changes, no symptoms and few risk factors, the provider will usually request a prompt repeat sample collected with careful technique: minimal tourniquet time, no fist pumping, an appropriate needle and drawing away from any running infusion. Treating a false result can drive potassium dangerously low.
If the ECG shows hyperkalaemic changes, the client is symptomatic or the risk is high, such as acute kidney injury, the result is treated as potentially real while the redraw is arranged. The haemolysis flag does not prove the value is false. The nurse's role is to bring the laboratory result, the specimen quality and the bedside findings together for the provider.
Distractors and an original study scenario
Imagine a hypothetical client admitted for pneumonia, with normal kidney function, whose potassium returns critically high with a note that the sample was haemolysed. The client is alert and the monitor shows unchanged sinus rhythm. The options are to give a prescribed potassium-lowering medicine, ignore the result, or assess, report and request a redraw. Assess, report and redraw is strongest.
Ignoring the result is unsafe because haemolysis does not exclude true hyperkalaemia. Treating at once skips the correlation that prevents harm. Change the stem so the client has acute kidney injury and peaked T waves, and the priority shifts to immediate escalation and treatment orders. Phlebotomists or assistive personnel can redraw, but the nurse interprets and escalates.
Documentation and preventing repeat haemolysis
Document the reported value, the haemolysis comment, the ECG findings, the client assessment and the time the provider was told, along with any orders received. When the repeat result returns, record it beside the first so the trend is clear. This prevents a later reader from treating the original haemolysed value as the client baseline.
If samples from the same client haemolyse repeatedly, look at the collection method: difficult veins, small catheters used for drawing and long transport times are common contributors. Discuss options with the phlebotomy team or provider. Many laboratories notify the unit when haemolysis is detected, and acting on that notice promptly shortens the time to a reliable result.
Sources and further reading
Acute Care Testing: Pseudohyperkalemia. Definition of pseudohyperkalaemia, in vitro haemolysis and collection factors as causes, haemolysis index, and repeat sampling.
AHRQ PSNet: A fatal twist in pseudohyperkalemia. Case of harm from treating a haemolysed potassium without correlating with the ECG, and system safeguards such as repeat sampling.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our dosage calculation and lab values practice questions are the closest set to what this page covers.
Common questions
Does a haemolysed sample mean the high potassium is false?
Not necessarily. Haemolysis can falsely raise potassium, but the client may still have true hyperkalaemia. Assess the ECG, symptoms and risk factors and report everything to the provider.
How can a nurse reduce haemolysis when drawing blood?
Keep tourniquet time short, avoid fist pumping, use an appropriate needle, fill and mix tubes gently, avoid drawing above an infusion and send specimens promptly.
When should a haemolysed high potassium be treated before a redraw?
When the ECG shows hyperkalaemic changes, the client has symptoms, or risk is high, such as kidney injury. The provider then orders treatment while confirmation is obtained.
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