Pseudohyperkalemia is defined as a spurious elevation of the serum potassium, which occurs when potassium is released from the within the cells into the blood serum in a blood sample collected for measurement of potassium level.
Fairly often, the potassium level detected during lab testing is a false reading. This is called factitious hyperkalemia, or pseudohyperkalemia. It is an unusual cause of hyperkalemia, which can lead to incorrect interpretation and wrong patient management.
This spurious elevation of K+ levels is due to hemolysis that occurs during or after the blood draw. Hemolysis is the rupture or breakdown of the red blood cells.
Causes of pseudohyperkalemia
This mechanism happens due to several reasons and they all relate to the happenings in the laboratory. It is caused by the lysis or mechanical rupture of the red blood cells, which leak their intracellular potassium into the serum.
This typically happens while drawing the patient’s blood into the syringe or shortly after that if the blood is kept for too long.
This gives a wrong high reading of serum potassium. It can similarly give a wrong impression when diagnosing hypokalemia. The various causes include
Hemolysis during puncturing the vein by either excessive vacuum in the syringe while drawing blood or due to the use of smaller gauge collection needle
Longer blood storage time
Prolonged storage of blood after the draw at room temperature will cause movement of potassium out of the cells or in the cold before doing the test
Wrong temperature for blood storage
The temperature at which the blood is stored is an important factor. Cold storage of whole blood samples before separation will not allow glycolysis
and the energy‐dependent Na+,K+‐ATPase enzyme will not maintain the
transcellular potassium gradient.
Conversely, storage above room temperature will initially cause falsely reduced potassium due to increased Na+,K+‐ATPase enzyme activity before glucose is completely used up and [K+] rises.
Too tight tourniquet and left for too long during draw
Wrong fist clenching
Longer and too tight fist clenching while blood was being drawn leading to efflux of potassium from the muscle cells into the blood.
Leukocytosis, thrombocytosis, and polycythemia
Leukocytosis (elevated white blood cells), thrombocytosis (elevated platelets), and polycythemia (increased red blood cells) all predispose to pseudohyperkalemia. Elevated concentrations of these cells increase the fragility of their membranes, which allows the leakage of potassium from within the cells into the blood.
In pediatric patients
In pediatric patients, factitious hyperkalemia can occur during phlebotomy, especially with heel-poke and finger-stick phlebotomy, which are commonly used in infants and small children.
Therefore, the ECG findings should always be used to correlate and when pseudohyperkalemia is suspected, another blood sample should be sent for testing ensuring that the blood is drawn correctly and processed quickly without delay.
Again, measuring whole blood potassium or lithium heparin plasma sample instead of serum potassium will usually verify the correct diagnosis.