Introduction:
Before we go to pseudohyperkalemia, let us understand hyperkalemia. Hyperkalemia is a rare, life-threatening condition in which potassium ions are released by the cells into the plasma (the liquid portion of the blood). This affects the cardiovascular system and nervous system the most, causing irregular heartbeats, chest pain, blockage in the heart, weakness, numbness, and paralysis. The most common causes of hyperkalemia are chronic kidney disease, certain drug intake, and pseudohyperkalemia.
What Is Pseudohyperkalemia?
As the name suggests,’ pseudo’ means false, and ‘hyperkalemia’ means increased potassium concentration in the blood. It is a faulty interpretation by the laboratories performing blood tests. Pseudohyperkalemia is a condition in which the serum potassium levels are raised compared to the normal plasma potassium level. This means the calculated value of potassium is higher, but the actual value of potassium is within the normal range. Pseudohyperkalemia is also known as spurious hyperkalemia, factitious hyperkalemia, and artifactual hyperkalemia. It was first reported in the 1950s among individuals with thrombocytosis- a condition with increased platelets (cells that help in blood clotting). There are different types of pseudohyperkalemia, namely, reverse pseudo hyperkalemia, familial pseudohyperkalemia, and seasonal pseudo hyperkalemia.
What Are the Types of Pseudohyperkalemia?
- Reverse Pseudohyperkalemia - This occurs when there is a high potassium concentration in the plasma and normal potassium in the serum. This is usually seen in leukemic individuals with a higher number of weak white blood cells. These cells rupture, releasing the potassium in the plasma.
- Familial Pseudohyperkalemia - Also known as ‘leaky cell syndrome’ is a rare genetic type of pseudohyperkalemia.
- Seasonal Pseudohyperkalemia - This form is temperature-dependent. Lower temperatures have been found to cause pseudohyperkalemia.
What Is the Mechanism Behind Pseudohyperkalemia?
The body needs potassium ions to properly function the heart and nerves and maintain optimum blood pressure. The normal range of potassium in the human body is 3.5-5.2 mmol/L. Potassium is usually found inside the cells (intracellular fluid), whereas sodium is present outside the cell (extracellular fluid). A slight disruption of the cell membrane by physical, chemical, or mechanical methods can lead potassium to leak out of the cells into the plasma. This causes a high potassium concentration.
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Mechanical Causes: During blood collection, repeated clenching of fist to identify a vein, painful puncture of the vein, using a smaller gauge needle, non-usage of evacuated tube collection systems, using excessive pressure while drawing blood, and applying tourniquet for a longer period of time may disrupt the blood cell membranes leading to leakage of potassium from intracellular fluid to extracellular fluid. During sample processing, vigorous shaking of the sample vials, forceful centrifugation, and re-centrifugation can also cause hemolysis leading to pseudohyperkalemia. In centrifugation, the serum or plasma passes through a compressed layer of gel. Whereas during re-centrifugation, the blood cells with a high concentration of potassium leak back into the serum.
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Temperature: Surrounding lower temperatures have also been associated with the release of potassium in the blood plasma. A delay in the processing of the blood sample when it is kept on ice or freezer for long causes disruption of the cells releasing potassium ions. Sodium and potassium exchanging ATPase is a compound responsible for properly maintaining sodium and potassium levels in the body. A lower than normal temperature decreases the activity of the compound, causing a shift of the potassium ions in the plasma.
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Storage and Transportation of the Blood Sample: The use of vacuum tubes, delay in transportation, and a time lag in sample procession utilize the stored glucose (blood sugar) and make the sodium-potassium exchanging ATPase pump fails, and potassium moves out of the cells.
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Contamination With Potassium: The most potent form of potassium contamination is the potassium salt K+EDTA added to the collection vials to prevent blood clotting. This happens when the blood is drawn to the EDTA vial rather than a sample bottle for potassium estimation.
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Potassium contamination can also occur if the blood is drawn from the arm used for administering the potassium-infused intravenous injection in certain individuals.
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Condition of the Individual: Broadly, there are three patient conditions that may cause pseudohyperkalemia. They are -
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An Increase in the Levels of Platelets (Thrombocytosis) - Platelets are the cells that help in a blood clot. In thrombocytosis, as the blood clots, potassium leaks into the plasma. So, the potassium concentration in the serum is higher than in the plasma.
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An Increase in the Levels of White Blood Cells - In individuals with chronic lymphocytic leukemia, the concentration of white blood cells increases. Some weak white blood cells rupture and release potassium into the plasma.
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An Inherited Defect in the Outer Layer of the Red Blood Cells - The genetic inheritance of certain defective protein that forms the outer layer of the red blood cells results in the rupture of the membrane causing potassium ions to move out of the cells. Splenectomy or removal of the spleen, a reservoir organ for platelets, has also been associated with increased serum potassium levels. Fear of getting punctured while drawing blood induced respiratory alkalosis (increased breathing), leading to hyperkalemia.
How Can Pseudohyperkalemia Be Avoided?
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Thorough training and educating the phlebotomist to avoid prolonged fist clenching, minimize tourniquet application time, and avoid re-pricks.
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Fist clenching should be avoided when the sample is collected for potassium estimation.
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Reducing the sample transportation time.
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Avoid prolonged storage of the samples on ice or in the freezer.
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Avoid repeating centrifugation on samples already being centrifuged once.
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Avoiding the use of vacuum tubes for sample collection.
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For patients who have undergone splenectomy, utmost precaution should be taken as they are predisposed to thrombocytosis leading to pseudohyperkalemia.
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Potassium estimation of blood done by a blood gas machine will give the correct diagnosis.
Conclusion-
Pseudohyperkalemia is a false interpretation of the serum potassium level. It is multifactorial. Early detection and diagnosis can prevent possible dangerous treatment, which might lower the actual potassium levels and cause hypokalemia. If pseudohyperkalemia is suspected, then the individual should be advised to get the samples tested again. Taking proper precautions and a mindful approach can keep a check on pseudohyperkalemia.