Workup for Hypophosphatemia - Differential Diagnosis Framework
Rule out spurious hypophosphatemia: paraproteinemia, acute leukemia
Measure Urine Fractional Excretion of Phosphate (FEPO4)
FEPO4 < 5%:
• GI Losses: Inadequate intake, Malabsorption, Chronic diarrhea, Poor absorption (Antacids, Phosphorus binders, Niacin, Vitamin D deficiency)
• Transcellular Shift: Refeeding, Glycolysis stimulation, TPN, Insulin/Glucose, Acute resp. alkalosis, Hungry bone syndrome, Tumor genesis syndrome
FEPO4 ≥ 5% - Renal Losses:
• Normal or High PTH: Primary or Tertiary hyperparathyroidism, Vitamin D deficiency/resistance, Bisphosphonates, Denosumab, Estrogen based Rx
• Normal or Low PTH:
- High FGF-23: Oncogenic osteomalacia, Ferric carboxymaltose, ADHR, XLHR
- Normal or Low FGF-23: Fanconi syndrome, CA Inh., Osmotic diuresis
Dr. Aisha Shaikh @aishaikh
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