Information on Falsely Elevated Potassium Test Results

Pseudohyperkalemia  - Falsely Elevated Potassium Tests Results

The causes of pseudohyperkalemia (PHK) include: Leaving the tourniquet on for more than 1 minute, excessive fist clenching, arm in an upward position, carryover of potassium-containing anticoagulants when tubes are not filled in the correct order of draw, drawing above an IV site, difficult/traumatic draw, use of small gauge needles, syringe/catheter draws, forced transfer of blood from the syringe into evacuated tubes, unpadded transport of samples in pneumatic tube systems, vigorous mixing of tubes,  delays in processing sample beyond 2 hours, chilling of whole blood beyond 2 hours before centrifugation and certain patient conditions.  

Many of the aforementioned causes introduce hemolysis, the rupture of red blood cells. At Bronson’s laboratories, all serum and plasma samples tested for potassium have a direct measurement of the level of hemolysis. That “serum index” allows for reporting the potassium (K⁺) result with a comment indicating how the results are affected for mild or moderate hemolysis. Samples with severe hemolysis are rejected and redrawn,

Some of the causes for PHK do not cause hemolysis. These are more difficult to detect. False increases in K⁺ can occur even when all collection, processing, and testing steps are performed correctly. One cause of a falsely increased potassium is an elevated WBC (typically over 50 x 10⁹/L ). This is particularly seen in conditions such as chronic lymphocytic leukemia (CLL). Studies have shown the false increase from CLL averages 1 mmol/L K⁺ per 100 x 10⁹/L WBC count. ²  In CLL, the WBCs are fragile and easily lysed to release their intracellular contents, which contain K⁺. Unlike the lysis of red blood cells, this increase in potassium cannot be measured by a serum index or grossly observed. The routine testing process for K⁺ includes several steps which can lyse the fragile WBCs. These include the transfer of the blood into a vacuum tube, potential rough handling during transport in an unpadded pneumatic tube system, and centrifugation to separate the cells from the plasma or serum required for testing by most chemistry analyzers. However, if one knows that the WBC count is significantly elevated with a condition like CLL, there is a way to obtain a more accurate K⁺ value for these patients. If the sample is collected directly into a blood gas syringe, carefully transported to the laboratory, and the request is made to test the sample on a whole blood analyzer (typically a blood gas machine), the results will be much more accurate.

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