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Hypophosphataemia (Low phosphate)
💉 IV phosphate if serum PO₄ < 0.32 mmol/L or severe symptoms. 🍽️ Low phosphate can trigger refeeding syndrome.
📏 About
- ✅ Normal range: 0.8 – 1.4 mmol/L
- 🚨 Severe: < 0.4 mmol/L (1.24 mg/dL)
🧬 Aetiology
- 🏥 Phosphate reabsorption in renal PCT
- 📉 Decreased uptake with PTH
🩺 Causes
| 🧾 Cause | 🤒 Clinical Features | 🔬 Investigations | 💊 Management |
|---|---|---|---|
| 🍽️ Refeeding Syndrome | Weakness, respiratory failure, arrhythmias, confusion after feeding malnourished patient | Check PO₄, Ca²⁺, K⁺, Mg²⁺; monitor during refeeding | Slow nutrition, PO/IV phosphate, close monitoring |
| 🍷 Chronic Alcoholism | Weakness, tremor, seizures; often with low Mg²⁺ & K⁺ | Serum PO₄, Mg²⁺, K⁺; LFTs, renal function | PO/IV phosphate, nutrition, treat alcohol dependence |
| 💉 Diabetic Ketoacidosis (DKA) | Occurs during insulin therapy: weakness, confusion | Glucose, ketones, PO₄, blood gases, K⁺, Mg²⁺ | IV fluids, insulin, phosphate if very low |
| 🦴 Hyperparathyroidism | Bone pain, stones, weakness; hypercalcaemia features | Ca²⁺, PO₄, PTH, urine phosphate | Treat underlying cause ± phosphate support |
| 🥀 Malnutrition | Fatigue, weakness, bone pain, infection risk | Serum PO₄, Ca²⁺, Mg²⁺, albumin; nutrition review | PO/IV phosphate, nutritional support |
| 🧪 Renal Tubular Disorders (e.g., Fanconi) | Polyuria, rickets/osteomalacia, growth delay | PO₄, Ca²⁺, bicarbonate, K⁺; urine glucose, amino acids | PO phosphate, bicarbonate & K⁺ supplements, treat cause |
| 💊 Medications (antacids, diuretics) | Weakness, bone pain, low phosphate symptoms | Check PO₄, Ca²⁺, Mg²⁺; review meds | Stop offending drug, PO phosphate, correct electrolytes |
| 🌬️ Respiratory Alkalosis | Cramps, tetany, confusion from hyperventilation | ABG, PO₄, Ca²⁺, K⁺ | Treat cause of hyperventilation, phosphate if severe |
🧠 Clinical Features
- Asymptomatic → muscle weakness, myalgia, rhabdomyolysis
- Seizures, delirium, tremor, paraesthesia
- Respiratory failure (weak diaphragm)
- Cardiac failure (myocardial weakness)
- Osteomalacia, haemolysis, coma
🔗 Associations
- Osteomalacia, bone pain, insulin resistance
- Glycosuria, hypercalciuria, hypermagnesaemia
🔬 Investigations
- U&E, Creatinine
- Ca²⁺, Mg²⁺, PO₄, ALP, VBG
💊 Management
- Mild (0.6–0.69 mmol/L)
- Usually outpatient: manage cause, diet rich in phosphate
- Oral replacement (e.g. Phosphate Sandoz)
- Moderate (0.4–0.59 mmol/L)
- Replace if symptomatic or high risk
- Phosphate Sandoz 1–2 tablets PO TDS
- If severe symptoms → IV phosphate (e.g. 25 mmol over 12h)
- Severe (<0.4 mmol/L)
- IV phosphate (e.g. 100 mmol in 500 mL over 8–12h)
- ⚠️ Avoid if hypercalcaemic or oliguric
⚠️ Cautions
- Rapid phosphate infusion → hypocalcaemia, calcification
- Renally cleared → use with caution in CKD