Overview
Hypophosphataemia refers to a reduced serum phosphate concentration of <0.8 mmol/L. This may occur in the context of reduced intake, compartmental shift or increased excretion of phosphate.
Aetiology
Causes of Hypophosphataemia
Reduced Intake / Uptake
- Severe malnutrition - starvation, alcoholism, anorexia, TPN
- Malabsorption
- Vitamin D deficiency
- Phosphate binders (CKD patients)
- Antacids
Compartmental shift
- Insulin - recovery post DKA, refeeding syndrome, insulin infusion, glucose infusion
- Severe respiratory alkalosis
- Hungry bone syndrome
Increased excretion
- Hyperparathyroidism
- Vitamin D deficiency
- Diuretics - acetazolamide, thiazides, loop diuretics
- Osmotic diuresis (e.g. poorly controlled diabetes)
- Iron infusion
- Post renal transplant
- Fanconi syndrome
Approach
Signs and Symptoms
Generally asymptomatic except for in severe hypophosphataemia.- Anorexia
- Lethargy
- Muscle weakness
- Seizures
- Coma
If the cause is not apparent, urinary phosphate (either 24-hour urine or fractional excretion) may be useful in differentiating increased excretion from other causes.
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