Electrolytes are minerals that carry electrical charges when dissolved in fluid. They regulate fluid balance, nerve signals, muscle contractions — including the heartbeat — and the body's acid-base balance. Your body maintains electrolyte levels within very tight ranges, and when they drift outside those ranges, the consequences can range from mild fatigue to cardiac arrhythmia.
An electrolyte panel is one of the most commonly ordered blood tests — routinely included in basic metabolic panels, pre-operative workups and monitoring for patients on diuretics, heart medications or IV fluids.
Sodium (Na)
Sodium is the dominant electrolyte in the fluid outside cells and plays the central role in regulating how much water the body retains. Normal range: 136–145 mmol/L.
Low sodium (hyponatraemia) — most commonly caused by excess water retention, kidney problems, heart failure, liver disease, or certain medications including antidepressants (SSRIs) and diuretics. Symptoms range from headache and confusion to, in severe cases, seizures.
High sodium (hypernatraemia) — usually indicates dehydration: the body has lost more water than salt. Less common, and typically corrected with fluid replacement.
Potassium (K)
Potassium lives primarily inside cells and is critical for heart rhythm and muscle function. Normal range: 3.5–5.0 mmol/L. The acceptable range is narrow — even modest deviations can be clinically significant.
Low potassium (hypokalaemia) — causes muscle weakness, cramps and, at severe levels, dangerous heart rhythm abnormalities. Common causes include diuretics (water tablets), vomiting, diarrhoea and poor dietary intake.
High potassium (hyperkalaemia) — can be equally dangerous to the heart. Causes include kidney failure (the kidneys regulate potassium excretion), ACE inhibitors, and certain potassium-sparing diuretics. Some medications are adjusted based on potassium levels precisely because of this risk.
Chloride (Cl)
Chloride is the main negatively charged electrolyte in blood and works closely with sodium to maintain fluid balance. It also forms part of the acid-base regulation system. Normal range: 98–106 mmol/L. Isolated chloride abnormalities are uncommon; they usually move in the same direction as sodium or indicate an acid-base disturbance.
Bicarbonate (CO₂ or HCO₃)
Bicarbonate acts as the body's main buffer against acids, keeping blood pH stable. Low bicarbonate suggests metabolic acidosis — the blood is too acidic, which can occur in kidney disease, uncontrolled diabetes (diabetic ketoacidosis), or severe diarrhoea. High bicarbonate suggests metabolic alkalosis, often caused by prolonged vomiting, diuretic use or potassium deficiency.
Calcium and magnesium
Some extended panels include calcium (important for bone, muscle and nerve function) and magnesium (involved in hundreds of enzymatic reactions including heart rhythm regulation). Both are worth asking about if you have muscle cramps, heart palpitations or bone density concerns.
Reading your panel as a whole
Electrolytes interact with each other and with the medications you take. A diuretic that lowers potassium may simultaneously affect sodium and bicarbonate. That's why doctors read the panel as a system, not as isolated numbers, and why medication adjustments often involve monitoring the whole panel rather than just one value.
If you're on long-term diuretics, ACE inhibitors, lithium or any medication that affects kidney function, regular electrolyte monitoring is standard of care — keep your results together over time so trends are visible.