Electrolytes

Potassium: normal range 3.5–5.0 mmol/L. Important in neuromuscular function. Low level, usually below 3.0 (hypokaleamia) can lead to cardiac arrhythmias. High level, usually above 5.5 (hyperkalaemia) slows heart rate and can cause cardiac arrest.

Calcium: total calcium 2.23–2.57 mmol/L, ionized calcium 1.15–1.27 mmol/L. Allows cardiac muscle to work without becoming tired. Ionized calcium (available for body to use). Low level can lead to decreased muscle contractility.

Sodium: normal range 135–145 mmol/L. Most of body’s sodium is in the extracellular fluid. Controls water distribution as well as extracellular volume. Hyponatraemia (usually below 135 mmol/L) = water into cells. Hypernatraemia (usually above 150 mmol/L) = water out of cells.

Phosphate: normal range 0.81–1.45 mmol/L. Intracellular. Critical component of adenosine triphosphate which the body uses as fuel. Also important in muscle function, red blood cells and nervous system. Hypophosphataemia: muscle weakness and reduced cardiac contractility. Hyperphosphataemia: reduced calcium levels, tingling of fingers. Precipitation of calcium phosphate in the kidney.

Magnesium: normal range 0.65–1.05 mmol/L.

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