Factitious causes of hyperkalaemia
Mild hyperkalaemia due to factitious causes are almost impossible to exclude. Potassium rises in warm weather, with exaggerated fist clenching and with delayed separation a rise in 1 mmol/L can occur in as little as 4 hours. In these cases as well as those due to refrigeration, there will be no visible signs of haemolysis. Potassium concentration is slightly higher in serum than plasma due to release from leukocytes and platelets; this is only significant with marked leucocytosis (> 100x10^9/L) or thrombocytosis (> 400x10^9/L).
A further common cause is contamination by K-EDTA which is used as an anti-coagulant in FBC tubes; a small amount can be transferred by collecting blood for a FBC before the biochemistry sample. In these cases, there may also be low concentrations of calcium, magnesium and alkaline phosphatase.
Intracellular potassium concentration is approximately 100 mmol/L and only small quantities are required to raise plasma concentrations. The commonest cause of release of intracellular potassium release is haemolysis but other causes include trauma, rhabdomyolysis and cell lysis with cancer chemotherapy.
Drug induced hyperkalaemia
Medications generally produce hyperkalemia either by causing redistribution of potassium (beta2 -adrenergic blockers, succinylcholine, digitalis overdose, hypertonic mannitol) or by impairing renal potassium excretion.
Drugs cause impaired renal potassium excretion by (1) interfering with the production and/or secretion of aldosterone (nonsterodial anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, angiotensin-II receptor antagonists, heparin, cyclosporin, and FK 506) or (2) blocking the kaliuretic effects of aldosterone (potassium-sparing diuretics, trimethoprim, pentamidine, and nefamostat mesilate).
It should be noted that since severe renal insufficiency is generally required to cause hyperkalemia, an elevated serum potassium concentration in a patient with mild-to-moderate renal failure should not be ascribed to renal failure alone.
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- Preston RA, Hirsh MJ, Oster MD Jr, Oster HR. Drug-induced hyperkalemia. Am J Ther 1998;5:125-32.
JHB 12 Nov 2009