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Electrolytes
Potassium (K)
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Potassium is the main intracellular cation; small changes in the extracellular concentration strongly affect cardiac and neuromuscular excitability.
Reference interval
| Conventional (mEq/L) | SI (mmol/L) | |
|---|---|---|
| Adults | 3.5–5 mEq/L | 3.5–5 mmol/L |
Specimen: Serum or heparinised plasma · Conventional × 1 = SI
Causes of high values
Hyperkalaemia: acute kidney injury and chronic kidney disease, potassium-sparing drugs (ACE inhibitors, ARBs, MRAs), acidosis, adrenal insufficiency, tissue breakdown and in-vitro haemolysis (spurious). ECG changes indicate urgency.
Causes of low values
Hypokalaemia: diuretics, vomiting, diarrhoea, hyperaldosteronism, magnesium deficiency, insulin and beta-agonist effects (redistribution) and renal tubular disorders.
Pre-analytical and method notes
Haemolysis, delayed separation, fist clenching, thrombocytosis or leucocytosis (pseudohyperkalaemia in serum) and EDTA contamination all raise measured potassium; repeat suspicious results. Reference limits vary slightly by laboratory and specimen type (plasma values are a little lower than serum).
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
- Brenner and Rector's The Kidney. Elsevier, 11th edition (2019) — Tier 3 (textbook)
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