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Artefactual hyperkalemia - dangerous, expensive. And preventable.

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Potassium is part of a renal profile, the most commonly ordered test in pathology. 
In N Devon we do just over 100000 primary care tests per year for a population of 160000 Assuming we are similar to others, that would be about 40 million primary care tests per year in the UK.
Most potassium in a blood sample sits inside the blood cells, and there is a large concentration gradient across the cell membranes. This is maintained through the the Na/K ATPase, which uses energy to drive sodium out of the cell, in return for potassium entering the cell. Because this is an enzymatic process it is extremely sensitive to environmental conditions. For instance, as temperature rises then the enzyme works faster, pumping more potassium out of the serum into the cell. Conversely, when it is cold the pump doesn't work well and potassium leaks out of the cells. All this means that the level of potassium in the serum can be affected by the conditions in which a non-stabilised sample is kept. When the…