What should you know about a sodium blood test?

Sodium is an electrolyte: a mineral that carries an electrical charge in body fluids. The test is often included in an electrolyte panel or metabolic panel and uses a blood sample taken from a vein. It may be requested as part of a general assessment or to investigate symptoms such as confusion, weakness, nausea, or unusual thirst.

A result outside the laboratory's reference interval does not identify a cause by itself. A low sodium level can occur when the body retains too much water, loses sodium, or receives less sodium relative to its fluid needs. A high level can be associated with too little body water or excess water loss.

Medicines, vomiting, diarrhoea, heavy sweating, kidney problems, hormone conditions, heart or liver disease, and changes in fluid intake can affect sodium. Your clinician interprets the result with your symptoms, medical history, examination, kidney function, and other electrolytes. Chronic kidney disease can be one condition considered when fluid and electrolyte control is difficult.

Follow the laboratory or clinician's instructions. Some blood tests taken at the same visit may require fasting, so check before eating or drinking anything other than the permitted fluids. Do not stop medicines or deliberately change your salt or water intake unless a clinician tells you to do so.

Tell the healthcare professional about prescribed medicines, supplements, recent illness, vomiting or diarrhoea, and changes in drinking habits. After the sample, keep pressure on the collection site as advised. Ask when the result will be available and whether another test is needed to confirm or explain it.

Seek urgent medical help for new confusion, extreme drowsiness, a seizure, loss of consciousness, severe weakness, or trouble breathing. These symptoms can reflect a serious disturbance in body fluids and need prompt assessment rather than home treatment.

Contact a clinician promptly if you have persistent vomiting or diarrhoea, cannot keep fluids down, marked thirst with very little urine, or worsening weakness. Bring the test report and a list of medicines if you are assessed.

Ask what your sodium result means alongside your other blood tests, whether a medicine or recent illness could have influenced it, and whether you need repeat testing. You can also ask which symptoms should prompt same-day care and whether your usual fluid, salt, or medication routine needs adjustment.