Definition

Pseudohyperkalemia is defined as a spurious elevation of the serum potassium, which occurs when potassium is released from within the cells into the blood serum in a blood sample collected for measurement of potassium level.

Pseudohyperkalemia is an in vitro (happening outside the body such as in a laboratory test tube) elevation in serum potassium without in vivo (in the body) increase and thus does not have symptoms and signs of hyperkalemia.

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+ (potassium) levels is due to hemolysis that occurs during or after the blood draw. Hemolysis is the rupture or breakdown of red blood cells.

Pseudohyperkalemia is a relatively common phenomenon in blood samples collected in primary care. It is most often caused by the wrong procedure of blood collection, inappropriate storage conditions of the blood sample, and delay in transport to the laboratory

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

Hemolysis during puncturing the vein by either excessive vacuum in the syringe while drawing blood  or due to the use of a smaller gauge collection needle

Longer blood storage time

Prolonged storage of blood after the draw at room temperature or in the cold will cause movement of potassium out of the cells 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.

The Na+/K+-ATPase is an enzyme that transports Na+ (sodium) and K+ across the cell membrane to maintain a low Na+ and high K+ concentration within the cells.

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.

Tight tourniquet

A tight tourniquet applied for a long time can cause pseudohyperkalemia through various mechanisms: hemolysis, the release of potassium from muscle, pH changes in the blood sample, hemoconcentration, and shift of water into the cells.

Wrong fist clenching

Longer and too-tight fist clenching while blood was being drawn leads to the 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.

Phlebotomy is the surgical opening or puncture of a vein in order to withdraw blood,

How to rule out pseudohyperkalemia? (Solution)

It is essential that pseudohyperkalemia be ruled out. The correct diagnosis of hyperkalemia is necessary because treatment of hyperkalemia in a patient whose potassium levels are normal can be dangerous.

The ECG findings of hyperkalemia are typical and should always be used to correlate with the report of the lab test. Additionally, 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.

Especially in the case of potassium assessment, labs should follow the correct protocol and develop guidelines for differentiating affected versus unaffected specimens.