Phosphate is the second most abundant mineral in your body after calcium. Around 85% of it sits in bones and teeth, where it combines with calcium to form the hard mineral structure. The remaining 15% is distributed across every cell in the body, where it forms part of ATP (the molecule cells use for energy), DNA, RNA, and the phospholipid membranes that surround cells. Without adequate phosphate, none of these processes function properly.
Blood phosphate levels are regulated by the kidneys, parathyroid hormone (PTH), and vitamin D working together. The kidneys determine how much phosphate is excreted or reabsorbed. PTH lowers blood phosphate by increasing kidney excretion, while vitamin D increases phosphate absorption from food. When any of these regulators are disrupted, phosphate levels shift accordingly, making this test a useful indicator of underlying problems in those systems.
Low phosphate (hypophosphataemia) is associated with malnutrition, vitamin D deficiency, overactive parathyroid glands, malabsorption, and certain medications. Symptoms include muscle weakness, bone pain, and fatigue. Refeeding syndrome, a potentially serious complication that occurs when malnourished patients resume eating, is characterised by a sharp drop in phosphate.
High phosphate (hyperphosphataemia) most commonly occurs in kidney disease, where the kidneys cannot excrete phosphate effectively. It can also be seen with underactive parathyroid glands or excess vitamin D. In the context of chronic kidney disease, persistently high phosphate contributes to vascular calcification and bone complications over time.
This test is typically ordered alongside calcium, vitamin D, and kidney function markers. A fasting sample is recommended, as food intake, particularly carbohydrate-rich meals, can temporarily lower phosphate levels and affect interpretation.
Suited to people investigating bone health concerns, kidney disease, parathyroid disorders, vitamin D metabolism issues, or metabolic bone conditions such as osteomalacia or rickets. Often ordered alongside calcium, vitamin D, and kidney function markers.
