Medical test · Chemistry & metabolic
Electrolytes
Also known as: sodium and potassium, serum electrolytes
The dissolved salts that set the water content of the body and the electrical behaviour of nerves, muscle and the heart: sodium, potassium, chloride, bicarbonate, calcium, magnesium and phosphate.
- Kind
- Test panel
- Categories
- Chemistry & metabolic
- Specimen
- Serum
- Method
- Chemistry analyser
- Terminology
- LOINC 24326-1
What it measures
| Measure | What it tells you |
|---|---|
| Sodium | Governs water balance; low sodium is the commonest electrolyte disorder in hospital. |
| Potassium | High or low levels cause dangerous heart rhythms. |
| Bicarbonate | The blood's main buffer; low in acidosis, high in alkalosis. |
| Calcium | Corrected for albumin; high in parathyroid overactivity and cancer, low after thyroid surgery and in vitamin D deficiency. |
| Magnesium and phosphate | Fall with malnutrition, alcohol and refeeding; matter for heart rhythm and muscle. |
Why it is ordered
- Confusion, weakness, seizures, palpitations
- Vomiting, diarrhoea, dehydration
- Kidney disease and diuretic treatment
- Before and after surgery
- Endocrine disease (adrenal, parathyroid)
How it is done
Venous blood; potassium is falsely high if the sample is squeezed or delayed.
Preparation. None.
Reading the result
| Finding | Usual meaning |
|---|---|
| Low sodium | Often too much water relative to salt: diuretics, heart or liver failure, SIADH, excess drinking |
| High potassium | Kidney failure, ACE inhibitors and spironolactone, tissue breakdown; needs an ECG |
| Low potassium | Vomiting, diarrhoea, loop diuretics, steroid excess |
| High calcium | Primary hyperparathyroidism or malignancy in most adults |
Reference ranges vary by laboratory, method, age, sex and clinical context; a result is read against the person, not a table.
Limitations
Blood levels do not always reflect total body stores (potassium is mostly inside cells). Haemolysed samples give spurious potassium.
Medicines monitored with this test
Each medicine page cites the official document that names this test in its monitoring plan.
Educational content. Reference ranges differ between laboratories, methods, ages and sexes, and results are always read against the person, the question asked and other findings. This page cannot interpret an individual result.