Phosphorus/Phosphate
Related Subjects:
| Calcium Physiology
| Hypophosphataemia
| Hyperphosphataemia
📖 About Phosphate
- Phosphorus (mainly as phosphate) is essential for:
- Structural molecules → DNA, RNA, phospholipids.
- Energy metabolism → ATP, glycolysis, oxidative phosphorylation.
- Signalling molecules → cAMP, phosphorylation pathways.
- Regulation is tightly controlled by:
- 🔗 Calcium levels
- 🦴 Parathyroid hormone (PTH)
- 🌞 Vitamin D
- 🩺 Renal function
- ⚠️ Malnourished or refeeding patients have ↑ risk of hypophosphataemia (refeeding syndrome).
⚡ When to Replace Phosphate
| Serum phosphate | Action |
|---|
| < 0.32 mmol/L | 🚨 Severe – replace immediately (risk of muscle weakness, respiratory failure, cardiac dysfunction). |
| 0.32–0.8 mmol/L | ✅ Replace if symptomatic or high risk (malnutrition, alcoholism, critical illness). |
| > 0.8 mmol/L | ℹ️ No replacement usually needed unless symptomatic. |
🍽️ Oral Replacement
- First-line for mild–moderate cases (if patient can tolerate PO).
- Common preparations: sodium phosphate, potassium phosphate.
- Dose: 30–60 mmol/day in 2–3 divided doses.
- Encourage dietary intake: dairy, meats, nuts, whole grains.
💉 Intravenous Replacement
- Indicated for: severe hypophosphataemia (<0.32 mmol/L), symptomatic patients, or those unable to take oral.
- Formulations: potassium phosphate or sodium phosphate IV.
- Dose: 0.08–0.16 mmol/kg IV over 6–12 h (adjust for severity & renal function).
- ⚠️ Administer slowly → risk of hypocalcaemia, hyperkalaemia, arrhythmias if given too fast.
🧪 Monitoring & Precautions
- Check serum phosphate, calcium, potassium, magnesium regularly during replacement.
- Use caution in renal impairment (↑ risk of hyperphosphataemia and ectopic calcification).
- Stop supplementation once phosphate normalises to avoid overcorrection.
💡 Teaching Pearl: Always consider refeeding syndrome in malnourished patients – hypophosphataemia is often the first clue.
