A normal blood phosphate level
A normal blood phosphate is 0.8-1.4 mmol/L.
What is phosphate?
Phosphate, or phosphorus, is a mineral that plays a vital role in many bodily functions, including:
- Bone and teeth formation: Phosphate is a key component of hydroxyapatite, the mineral that gives bones their strength and rigidity
- Energy production: Phosphate is used in the body’s energy metabolism
- Cell function: Phosphate is a building block for cell membranes, DNA, and RNA
- pH balance: Phosphate helps regulate the body’s pH balance
Phosphate disorders are rare, and most are secondary to other diseases – i.e. not primary phosphate excess or deficiency. We will now go through them.
5 causes of a low blood phosphate (hypophosphataemia)
-
Nutritional: malnutrition, starvation, alcohol excess. Inadequate dietary intake of phosphate can lead to hypophosphataemia. Poor intake may be due to poor diet, including eating disorders such as anorexia nervosa, difficulty with chewing and swallowing, and alcohol dependency
-
Recovery from severe illness – especially when patients start to recover and move from a catabolic state to an anabolic state
- Vitamin D deficiency – including hypophosphataemic rickets
-
After renal transplantation. Hypophosphataemia is common after renal transplantation, especially after long periods of dialysis
- Rare kidney disorders: Certain kidney disorders, such as tubular diseases (like Fanconi syndrome, Dent’s disease), can impair phosphate reabsorption.
Other causes
- Excess gut phosphate binders – e.g. calcium carbonate/acetate or aluminium hydroxide
- Drugs causing renal phosphate leak – including aminoglycosides, cisplatin and tenofovir
- Diabetic ketoacidosis treatment (insulin drives phosphate into cells)
- Refeeding syndrome – carbohydrate refeeding after fasting. Other risks of refeeding include low potassium, low magnesium, low calcium and abnormal glucose metabolism
- Acute respiratory alkalosis
- Hungry bone syndrome (increased uptake by bone matrix) which occurs after parathyroidectomy
- Leukaemia or lymphomas.
5 causes of a high blood phosphate (hyperphosphataemia)
-
Chronic kidney disease (CKD, commonest cause): Impaired kidney function can lead to phosphate accumulation in the blood
-
Diabetic ketoacidosis – can cause phosphate release from cells
-
Rhabdomyolysis/crush injury: Muscle damage can release phosphate into the bloodstream
-
Hypoparathyroidism: Underactive parathyroid glands can lead to increased phosphate levels
-
Excessive phosphate intake – rare.
Other causes
- Laxatives and enemas: Using phosphate-containing laxatives or enemas frequently can cause hyperphosphatemia
- Excess vitamin D intake
- Acromegaly
- Thyrotoxicosis
- Acute respiratory acidosis
- Rare genetic disorders – e.g. pseudohypoparathyroidism.
Note on hyperparathyroidism (hyperPTH)
Phosphate levels vary depending on the type of hyperPTH
- Primary – phosphate levels are low, whilst calcium levels are high
- Secondary (less advanced CKD) – variable (usually normal/higher phosphate, normal/lower calcium)
- Tertiary (advanced CKD) – phosphate and calcium are high.
Other resources
