Patients with hypocalcaemia should have their calcium corrected before replacing phosphate to prevent further hypocalcaemia. Parenteral phosphate is usually given IV when serum phosphate is < 0.32 mmol/L or severe symptoms. A low phosphate can precipitate the refeeding syndrome.
- Normal range 0.8 - 1.4 mmol/L
- Severe is < 0.4 mmol/L (1.24 mg/dL).
- Phosphate reabsorption in renal PCT
- Decreased uptake with PTH
- Severe Respiratory alkalosis
- Severe DKA: Insulin moves phosphate into cells
- Refeeding syndrome after fasting/starvation
- Chronic diarrhoea, Antacids
- Post parathyroidectomy, Severe burns
- Poor diet or Malabsorption or Vomiting
- Gut phosphate binders, e.g. sevelamer
- Vitamin D deficiency, Hyperparathyroidism
- Alcohol withdrawal, Diuretics
- Renal losses, Renal tubular defects - Fanconi syndrome
- Tenofovir treatment
- Hypophosphataemic rickets
- Vitamin D-dependent rickets types I and II
- Asymptomatic, Muscle weakness, myalgia, rhabdomyolysis
- Seizures, delirium, diaphragmatic weakness
- Paraesthesia, Convulsions, Tremor, Haemolysis
- Respiratory failure due to weak resp muscles
- Cardiac failure from muscle weakness
- Oseomalacia, Coma can be seen
- Osteomalacia, bone pain, reduced
- Glycosuria, hypercalciuria and hypermagnesaemia
- Check U&E Creatinine
- Ca, Mg, PO4, ALP, VBG
- Mild Hypophosphataemia (0.6-0.69mmol/L)
- Manage cause and monitor. Oral replacement may be considered see below. Manage as outpatient. Guidelines differ in threshold for treatment.
- Oral phosphate and diet rich in phosphate e.g. protein and dairy
- Moderate Hypophosphataemia (0.4-0.59mmol/L)
- Consider phosphate replacement if the patient is symptomatic or following a consideration of the clinical risks and benefits.
- Consider Phosphate Sandoz 1-2 tablets PO TDS
- Symptomatic consider 25mmol (250ml) over 12 hours IV Phosphate Polyfusor
- Severe Hypophosphataemia (<0.4 mmol/L)
- IV Phosphate Polyfusor IVI (100mmol PO4 in 500mL) given over 8-12 hours. Do not give IV phosphate to a patient who is hypercalcaemic or oliguric.
- Rapid rates of phosphate administration can lead to hypocalcaemia, hyperphosphataemia, and metastatic calcification.
- Phosphate is renally cleared. Phosphate (especially via the intravenous route) should be used with caution in patients with renal impairment.