Hypophosphataemia

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Normal range: 0·8 to 1·5mmol/L

These guidelines do not apply to critically ill patients or to patients at risk of refeeding syndrome. For refeeding syndrome please see Policy for prevention and management of refeeding syndrome in adults

Aetiology

Note - most patients with hypophosphataemia will have refeeding syndrome

1.    Reduced phosphorus intake:

  • TPN without phosphorus supplement
  • impaired intake, absorption or activation of Vitamin D
  • overuse of phosphate-binding antacids eg calcium carbonate, calcium acetate, aluminium hydroxide

2.    Redistribution of phosphorus from extracellular fluid (ECF) into bone, soft tissues or intracellular fluid (ICF):

  • diabetic ketoacidosis
  • hyperosmolar non-ketotic coma
  • alcohol withdrawal

3.    Increased renal elimination:

  • primary hyperparathyroidism
  • diuretics
  • acute renal failure with loss of tubular reabsorptive capacity
Risk Factors for refeeding syndrome (refer to guidance on refeeding syndrome as above)

Patients with any of the following:

  • BMI <16kg/m²
  • Unintentional weight loss >15% within the last 3 to 6 months
  • Little or no nutritional intake for more than 10 days
  • Low levels of potassium or phosphate or magnesium prior to feeding.

Patients with 2 or more of the following:

  • BMI <18·5 kg/m²
  • Unintentional weight loss >10% within the last 3 to 6 months
  • Little or no nutritional intake for more than 5 days
  • A history of alcohol abuse or drugs including insulin, chemotherapy, antacids or diuretics.

Patients with normal pre-feeding levels of potassium, magnesium and phosphate can still be at risk of refeeding syndrome. Refeeding syndrome can occur in patients fed orally, enterally or parenterally. It is less likely to occur in those fed orally since starvation is usually accompanied by a reduction in appetite however caution should be taken when prescribing oral nutritional supplements.

Clinical Features (usually only evident with phosphates below 0•3; if this is the case consider refeeding)
  • muscle weakness
  • anorexia
  • paraesthesia
  • seizures
  • haemolytic anaemia
  • cardiomyopathy and arrhythmias
  • osteomalacia
  • respiratory insufficiency due to muscle weakness
Hypophosphataemia Treatment Regimen

Give phosphate supplementation daily until phosphate more than 0·5mmol/L

 Repeat IV according to result until level more than 0·3mmol/L. All above doses should be halved in patients with eGFR less than 30mL/min.

Phosphorus level  Action  Monitor 
Greater than 0·5 to 0·8mmol/L  No supplementation is required if dietary intake adequate (refer to refeeding – see link above) Check phosphate after 24 hours as well as adjusted calcium, potassium and other electrolytes
0·3 to 0·5mmol/L Asymptomatic patients may not need to be treated but options are:

Oral: 2 Phosphate Sandoz® tablets (32mmol phosphate) daily.

Via enteral feeding tube: dissolve tablet(s) in 50mL water. Stopping feed is not required.

IV: Peripheral Administration – Dilute 10mL of Glycophos® (10mmol phosphate) into 250mL of glucose 5% or sodium chloride 0.9% and infuse over 12 hours (off label).

All above doses should be halved in patients with eGFR less than 30mL/min.

Check potassium, phosphate and adjusted calcium every 24 hours
Less than 0·3mmol/L IV: Peripheral Administration – Dilute 20mL of Glycophos® (20mmol phosphate) in 500mL of glucose 5% or sodium chloride 0.9% and infuse over 12 hours (off label). Check adjusted calcium, phosphate, sodium, magnesium & potassium every 12 hours.

 All infusions must be administered via an infusion pump. 

ECG monitoring is not required for the rates of infusion stated in this guideline. 

  • Glycophos® 20mL vial contains 20mmol of phosphate and 40mmol of sodium (as sodium glycerophosphate). This is an unlicensed use which should be explained to the patient.
  • Avoid in patients with hypernatraemia.
  • High doses of phosphate especially at rapid infusion rates can cause hypocalcaemia and metastatic calcification.
  • Once within normal range monitor phosphate, adjusted calcium and potassium levels twice weekly until levels are stabilised.