Have you ever been called by LifeLabs with a patient’s critical potassium that is normal following a repeat at a hospital?
This phenomenon, pseudohyperkalemia, is defined as a spuriously high potassium result in the absence of visible sample hemolysis or chronic kidney disease. It is typically due to the release of potassium from intracellular stores either during or following blood collection. The most common causes occur during the collection process e.g. mechanical trauma of red blood cells, fist clenching or prolonged standing of sample at room temperature. To illustrate the importance of collection, one urology clinic found its rate of unexplained hyperkalemia to decline from 16.0% to 3.8% with a revised protocol1.
Potassium may also be misleadingly elevated in the presence of extreme thrombocytosis or leukocytosis though the underlying causes differ. Platelets inherently release their potassium during the clotting process, causing a potassium increase of about 0.15 mmol/L per 100×109/L which is negligible in typical samples but will become significant when platelets exceed about 500×109/L2. White cells, by contrast, may release potassium during centrifugation, a situation further aggravated in conditions such as CLL where very high WBC counts are combined with greater membrane fragility.