Calcium

This is the harmonised UK adult range; UK labs usually print an adjusted calcium alongside it and doctors read that one when albumin is unusual.

Calcium is the mineral that gives bone its strength and is also needed for nerves, muscles and blood clotting. About half the calcium in blood is bound to albumin and half is free. This test measures the total calcium in a blood sample, before any allowance is made for the albumin level.

It is part of the bone profile. Doctors use it when looking into bone, kidney and parathyroid conditions, unexplained tiredness, kidney stones, and in some cancers. In the UK the adjusted calcium printed next to it is usually the figure doctors read.

• Overactive parathyroid glands
• Dehydration or a tight tourniquet, which concentrates albumin and so total calcium
• Some cancers
• Large intakes of vitamin D or calcium supplements
• Water tablets of the thiazide type, and lithium
• Being bedbound for a long time

• Low albumin, which lowers total calcium without changing the free calcium
• Low vitamin D
• Reduced kidney filtering
• Underactive parathyroid glands, including after neck surgery
• Low magnesium
• Some medicines used for bone, and some epilepsy medicines

• Total calcium moves with albumin, so an unwell person with a low albumin has a low total calcium that means little; this is why labs print an adjusted value
• A tight or prolonged tourniquet raises it
• Blood taken from an arm with a drip running can read very high or low

No fasting needed. Avoid a prolonged tourniquet. Usually interpreted through the adjusted calcium and alongside phosphate, albumin, PTH and vitamin D.

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