Electrolytes
Potassium
Potassium is the principal intracellular cation and a tightly regulated electrolyte essential for nerve conduction, muscle contraction and cardiac rhythm. Point-of-care testing delivers a rapid whole-blood result that supports urgent decisions in emergency, critical care, dialysis and pre-hospital settings.
Why it is measured
Both low and high potassium can trigger dangerous cardiac arrhythmias, so a fast near-patient result lets clinicians act sooner than a central laboratory turnaround would allow. It is a core component of any acute electrolyte assessment.
| Typical range | Indicative adult range approximately 3.5 to 5.0 mmol/L measured in whole blood or plasma by ion-selective electrode on POCT analysers. Serum values typically run about 0.2 to 0.4 mmol/L higher because potassium is released from platelets and cells during clotting. Ranges vary by method, sample type and analyser, so always use the local reported interval. |
|---|---|
| Sample | Whole blood (arterial, venous or capillary), collected into a balanced heparin syringe or cartridge and analysed promptly. Some bench POCT systems also accept lithium-heparin plasma. Avoid EDTA tubes and any potassium-containing fluid contamination. |
| Turnaround | Typically under 2 minutes from sample to result on cartridge or cassette blood gas and electrolyte analysers. |
Point of care devices that report it
- Abbott i-STAT 1 / i-STAT Alinity (CHEM8+, CG8+ and EC8+ cartridges)
- Siemens Healthineers epoc Blood Analysis System
- Radiometer ABL90 FLEX PLUS and ABL800 FLEX
- Roche cobas b 221 and cobas b 123 POC systems
- Nova Biomedical Stat Profile Prime Plus
- Siemens Healthineers RAPIDPoint 500e
Questions, answered
Why might a POCT whole-blood potassium differ from the laboratory serum result?
Whole-blood or plasma potassium measured by ion-selective electrode tends to read about 0.2 to 0.4 mmol/L lower than clotted serum, because potassium is released from platelets and other cells as blood clots. Sample type, time to analysis and method all contribute. Compare like with like and follow local policy on when to confirm a near-patient result against the central laboratory.
What preanalytical factors can falsely raise or lower a POCT potassium?
Haemolysis from vigorous aspiration, fine needles, prolonged tourniquet or fist clenching, and delayed analysis is the commonest cause of falsely high readings. Contamination with potassium-containing fluids or carry-over from EDTA can also raise results. Many analysers flag suspected haemolysis; careful sampling and prompt analysis reduce these errors. This is operational guidance and not a basis for changing treatment.
How quickly can POCT deliver a potassium result and why does that matter?
Cartridge or cassette analysers usually report potassium within about two minutes from a small whole-blood sample. Rapid results support timely decisions in cardiac arrest, suspected severe hyperkalaemia and dialysis monitoring, where waiting for the central laboratory could delay care.