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



#Hypophosphatemia #Differential #Diagnosis #Framework #Workup #phosphate #nephrology