Potassium is the main electrolyte inside your cells and plays a direct role in heart rhythm, muscle contraction, and nerve transmission. The body maintains blood potassium within a narrow range (typically 3.5 to 5.0 mmol/L), and even small shifts outside that range can have noticeable effects. Low potassium causes muscle weakness, cramps, and fatigue. High potassium, particularly above 6.0 mmol/L, can cause dangerous changes to heart rhythm and is treated as a medical emergency.
The kidneys are the primary regulators of potassium balance. They adjust how much is excreted based on intake, hormonal signals, and acid-base status. When kidney function declines, the ability to clear excess potassium is reduced, which is why potassium monitoring is routine in people with chronic kidney disease. Adrenal hormones, particularly aldosterone, also influence how the kidneys handle potassium.
Many common medications affect potassium levels. Diuretics (especially thiazide and loop diuretics) can drive potassium down, while ACE inhibitors, ARBs, and potassium-sparing diuretics (such as spironolactone) can push it up. For anyone on these medications, periodic potassium testing helps ensure levels remain within a safe range.
Falsely elevated potassium results are not uncommon. Haemolysis, where red blood cells break down in the collection tube before analysis, releases intracellular potassium into the sample and produces a reading that does not reflect your actual blood level. Clenching your fist during collection can also cause localised potassium release from muscle cells. The laboratory will flag a haemolysed sample, and a repeat test may be needed.
Potassium is almost always interpreted alongside sodium, kidney function tests, and the clinical context. It forms part of routine electrolyte panels and is one of the most frequently ordered blood tests in medicine.
To screen for or investigate hypokalaemia (low potassium) or hyperkalaemia (high potassium), monitor patients on medications that affect potassium (diuretics, ACE inhibitors, ARBs, digoxin), assess kidney function, and investigate symptoms of electrolyte disturbance.
