Phosphate

The range is higher in children and teenagers because bone is growing; it also moves with the time of day and with meals.

Phosphate is a mineral that, together with calcium, makes up most of the structure of bone and teeth, and it is also used by every cell for energy. Its blood level is set by the kidneys, the gut, vitamin D and parathyroid hormone. The test measures the concentration in a blood sample.

It is part of the bone profile and is checked in kidney disease, in bone and parathyroid conditions, in people being fed after a period of poor intake, and when calcium is being investigated.

• Reduced kidney filtering, the commonest cause of a sustained rise
• Underactive parathyroid glands
• Large vitamin D intake
• Tissue breakdown after injury or chemotherapy
• Phosphate-containing laxatives or enemas
• Growth in childhood and adolescence

• Overactive parathyroid glands
• Low vitamin D
• Refeeding after a period of poor nutrition, or heavy alcohol use
• Some antacids that bind phosphate in the gut
• Certain kidney conditions where phosphate leaks into the urine
• A recent carbohydrate meal or insulin, which moves phosphate into cells for a few hours

• A meal shortly before the test lowers it for a few hours
• Cells breaking down in the tube (haemolysis) or a delayed sample raise it
• It is naturally higher in the morning and in younger people in the general population

Best taken fasting in the morning, as meals move it. Interpreted alongside calcium, PTH and vitamin D.

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