Magnesium

Some labs print 0.66 to 1.07 or 0.7 to 1.05; the range is slightly lower in pregnancy.

Magnesium is a mineral found mostly inside cells and in bone, where it supports hundreds of chemical reactions, nerve signalling and muscle function. Only about one per cent of the body's magnesium is in the blood, so the blood level is a rough guide to the body's store. The test measures the concentration in a blood sample.

Doctors request it when someone has muscle cramps, palpitations or a low potassium or calcium that will not correct, when taking medicines known to lower it, and in people with gut or kidney conditions that affect absorption or loss.

• Reduced kidney filtering
• Magnesium-containing antacids, laxatives or supplements in large amounts
• Dehydration
• Underactive thyroid or adrenal glands

• Stomach-acid tablets (proton pump inhibitors) taken long term
• Water tablets
• Diarrhoea, coeliac disease and other gut conditions that reduce absorption
• Heavy alcohol use
• Poorly controlled diabetes
• Some chemotherapy and antibiotic medicines

• Cells breaking down in the tube (haemolysis) release magnesium and raise the reading
• Blood magnesium can sit within range while body stores are low, and the other way round
• Different labs use slightly different ranges

No fasting needed. A haemolysed sample is unreliable and is usually repeated.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.