Hyperphosphataemia (High phosphate)
⚠️ Hyperphosphataemia is common in patients with kidney disease and can lead to vascular and soft tissue calcification if not recognised and treated early.
📖 About
- Hyperphosphataemia = elevated phosphate in the blood.
- Common in chronic kidney disease (CKD) and acute kidney injury (AKI).
📊 Aetiology / Definition
- Serum phosphate >4.5 mg/dL (>1.46 mmol/L).
- 🩺 Reduced GFR → decreased phosphate excretion.
- ⬇️ PTH or pseudo-hypoparathyroidism → increased tubular phosphate reabsorption.
🔎 Causes
- ⛔ CKD stages 3–5 or AKI (most common).
- 💊 Phosphate-containing enemas or laxatives.
- 🧬 Tumour lysis syndrome or rhabdomyolysis (massive cell breakdown).
- 🦴 Endocrine: Hypoparathyroidism & pseudohypoparathyroidism.
🧑⚕️ Clinical Features
- Often asymptomatic (detected biochemically).
- 🩻 Can cause metastatic calcification in vessels/soft tissue.
- 📈 Chronic phosphate retention → secondary hyperparathyroidism.
- Severe cases: tetany, pruritus, red eyes (calcific conjunctivitis).
🔬 Investigations
- Check U&E, creatinine, phosphate (P), calcium (Ca), magnesium (Mg), potassium (K).
- 🔄 Look at calcium–phosphate product (risk of calcification if >55 mg²/dL²).
- 📈 PTH: Elevated in secondary hyperparathyroidism due to CKD.
💊 Management
- 👩⚕️ Treat underlying renal disease.
- 🥗 Dietary phosphate restriction (avoid cola drinks, dairy, processed foods).
- 💊 Phosphate binders (e.g., Sevelamer, Lanthanum, Calcium acetate).
- 💧 IV fluids: improve GFR & phosphate excretion (useful in AKI/TLS).
- 🧬 Tumour lysis syndrome: IV saline, allopurinol/rasburicase, dialysis if refractory.
- Dialysis in severe symptomatic hyperphosphataemia with renal failure.
💡 Pearls
- Always interpret phosphate in context of calcium - high phosphate + low calcium → neuromuscular irritability.
- Long-term complication: vascular calcification → accelerated atherosclerosis in CKD patients.
- Phosphate binders are taken with meals to block absorption.
- Dialysis patients: serum phosphate control is crucial to reduce cardiovascular risk.
📚 References
