Magnesium blood test: what to know

A clinician may request the test for muscle cramps, weakness, tremor, abnormal heart rhythm, ongoing diarrhoea or suspected poor absorption. Certain medicines and kidney problems can alter magnesium. A blood result does not always explain every symptom, and the laboratory range should be read with the clinical context.

Other tests may include salts such as potassium and calcium, kidney function, or a blood count when conditions such as [Anaemia](/conditions/anaemia/) are being considered.

Tell the clinician about supplements, antacids, laxatives and prescribed medicines. Do not change treatment to improve a result unless advised. A small blood sample is taken, and mild bruising can occur. If the result is outside range, the next step may be repeat testing, medicine review or investigation of diet, absorption and kidney function.

Seek urgent help for chest discomfort, fainting, severe weakness, confusion, seizures or a new irregular heartbeat. Arrange follow-up when abnormal results accompany persistent diarrhoea, vomiting, weight loss or symptoms of kidney disease. Do not interpret a result in isolation.

Why was magnesium checked, and were potassium, calcium and kidney function tested too? Could a medicine or absorption problem such as [Coeliac Disease](/conditions/coeliac-disease/) be relevant? When should the result be reviewed?