PhosphateSerum phosphate · Inorganic phosphate · PO4
A mineral partnered with calcium in bone and central to the body's energy currency.
Phosphate is stored mostly in bone alongside calcium, and the amount in blood is regulated by the kidneys and the same hormones that control calcium. It is also a building block of ATP, the molecule cells spend to do work, and of DNA.
It matters as a kidney and bone-metabolism marker: failing kidneys retain it, and it moves in the opposite direction to parathyroid hormone activity, so it is read alongside calcium rather than separately.
In practice levels vary through the day and dip after eating carbohydrate, so timing affects the result. It is interpreted with calcium, vitamin D and kidney function together.