Potassium in serum, plasma (K+)
Potassium is a routine test for all forms of imbalances in the water/electrolyte balance and the acid/base balance. The analysis is used in examination of hypertention and kidney failure, and in monitoring patients with kidney failure treated with diuretics (more about potassium transport in the kidneys).
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Potassium in plasma | 3,5-4,4 mmol/L |
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Potassium in serum | 3,6-4,6 mmol/L
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The element potassium is found in the body as monovalent cations. Almost all of the potassium is found intracellularly where the concentration is 30-50 times higher than extracellularly. The daily intake is 50-100 mmol, and secretion of potassium occurs in the kidneys and is controlled by aldosterone.
Potassium must always be considered in relation to the patient's acid-base status. Alkalosis leads to lower concentrations of potassium in the blood than normal, and acidosis to higher levels. This means that in an acidosis, a normal potassium level reflects a potassium deficiency.
Causes of hyperkalemia:
- Excess potassium is either due to rapid intravenous administration or reduced secretion in the kidneys. Reduced renal secretion can be caused by oliguric kidney failure, potassium-sparing diuretics, hyperkalemic type I renal tubular acidosis, and primary adrenal gland failure (Mb Addison).
- Shift in potassium from the intracellular to the extracellular space: reduced insulin activity, increased loss from cells due to necrosis, acidosis, hypoxia, hypo- or hyperthermia, hemolysis, digitalis poisoning, and use of beta blockers.
Causes of hypokalemia:
- Potassium deficiency: reduced intake or increased loss from the gastrointestinal tract (vomit, diarrhoea, laxatives). Increased secretion in the kidneys due to diuretics, metabolic alkalosis, metabolic and respiratory acidosis, increased mineralocorticoid activity, and magnesium deficiency.
- Shift from the extracellular to the intracellular space: metabolic alkalosis and compensation of acidosis, beta2-stimulating substances, and other causes of increased catecholamine activity.
Sources of error: Hemolysis due to the use of tourniquet and muscle pumps during blood tests, substantial thrombocytosis or leukocytosis.
Read more about potassium
i The handbook on medical biochemistry