Background
Phosphate is an element which is absorbed through our diets. Found in dairy, grains and meats.
Required for many of the processes in the human body:
- Essential constituent of cytoplasm
- Intracellular compounds
- Bone formation
- Neuromuscular functioning
Phosphate is absorbed in the GIT distal to the duodenum (aided by Vit D) and excreted via the kidneys (aided by PTH).
Normal serum levels: 0.8 - 1.3mmol/L.
Major stores of phosphate:
- Bone (85%)
- Intracellular (in soft tissues) (14%)
- Extracellular fluid (1%)
Aetiology hypophosphataemia
↓ GI Absorption
- Alcoholism (commonest)
- Vitamin D deficiency
- Malabsorptive disease
- PO4 binders
- Ca2+
- Al3+ / Mg2+ antacids
- TPN
- Fasting states (anorexia)
↑ renal excretion
- Hyperparathyroidism
- Glycosuria (DKA)
- Osteomalacia (tumour induced)
- Renal tubular acidosis
- Acute tubular necrosis
- HypoMagnesaemia / HypoKalaemia
- Multiple myeloma
- Fanconi syndrome:
- Proximal tubular dysfxn
- Wilson's disease (children)
- Cystinosis (children)
Metabolic conditions
- Resp. alkalosis
- Hungry bone synd.
- DKA
- Starvation refeeding
Other
- Medications
- Anabolic steroids
- Diuretics
- Sever burns
Clinical
Mechanism |
Early signs PO4 1-2mg/dl |
Late signs PO4 <1mg/dl |
| Dysfunctional bone metabolism |
↓ Bone Mineralisation Bone pain |
Rickets (children) Osteomalacia (adults) |
| Intracellular ATP | ↓ Myocardial contractility Proximal muscle weakness Muscle pain ↑RBC rigidity Encephalopathy |
Heart Failure Arrythmias Rhabdomyolysis Haemolysis Seizures/Coma |
| ↓ RBC 2,3 DPG | ↑ affinity of Hb for O2 | Systemic ischaemia Leucocyte & platelet dysfunction |
Management ↓PO4
Treat the underlying cause.
- Asymptomatic with PO4 > 0.65mmol/L - No repletion necessary
- Symptomatic or PO4 0.65 - 0.8mmol/L - Oral Na+ phosphate /K+ phosphate salts
- PO4 <0.32mmol/L - PO phosphate if asymptomatic, IV phosphate if symptomatic
- Patients with ongoing urinary losses will require ongoing repletion even after serum PO4 is normalised
- Dosing of IV phosphate, based on mmol/kg of body wt., varies on serum PO4 and symptoms
Investigations
FE PO4-3 = x100
Links
- CUH Intranet only Pharmacy Guideline on Mx ↓PO4-- solution dilutions