Hypophosphatemia

Hypophosphatemia

• Definition: Phosphate <2.5 mg/dl, signs and symptoms at <1 mg/dl
• Etiology
  • Results in decreased ATP formation, decreased 2,3-DPG, resulting in decreased O2 release in hypoxemic tissues
  • Decreased Net intestinal Absorption
    • Phosphate Binders
    • Alcoholism/Malabsorption
    • Burns
    • Vitamin D deficiency
• Impaired phosphate absorption in the gut and increased phosphate excretion - Antacids - Chronic Diarrhea
  • Transcellular shift of phosphate from the ECF to ICF
    • DKA
    • Respiratory alkalosis
    • Refeeding Syndrome
  • Increased Renal Excretion
    • Urinary Wasting (Fanconi Syndrome, Tumor-induced Osteomalacia)
    • Diuretics (loops, acetazolamide, thiazides)
    • Osmotic diuresis
    • Auto-diuresis
    • Post-ATN or post-obstructive polyuria
    • Hypothermia
    • CRRT
    • Meds
      • Aminoglycosides, IV iron, Tenofovir
      • Imatinib, VEGF inhibitors, temsirolimus
    • Primary Hyperparathyroidism
      • Hungry Bone Syndrome - Osteogenic Osteomalacia
  • Pseudo-hypophosphatemia
    • Hyperbilirubinemia
    • Acute leukemia
    • Mannitol
    • Paraproteinemia
• Symptoms
  • Seizures, paresthesias, tremors
  • Confusion, Central pontine myelinolysis
  • Impaired heart contractility, heart failure
  • Rhabdomyolysis
  • Insulin resistance, Hemolysis
  • Respiratory muscle weakness
    • Difficulty to wean off ventilator
  • Neurologic symptoms: paresthesia, dysarthria, confusion, seizures, coma
• Labs
  • Rarely, Hemolytic anemia, platelet dysfunction
• Complications
  • Rhabdomyolysis
  • HF
  • Impaired diaphragmatic function
• Diagnosis: Fraction or 24-hour Urine Phosphate - Urine excretion >100 mg or >5% fractional: Excessive renal loss
• Hyperparathyroidism, VitD - Urine excretion <100 mg or <5% fractional: Everything else
  • Next: Serum Calcium
  • Then: Aminoaciduria, glycosuria
• Treatment
  • Mild 2.0-2.5: Nothing
  • 1) Moderate to severe renal failure:
    • Caution, give 50% less
  • 2) Abnormal Calcium
    • Hypercalcemia: May risk calciphylaxis
    • Hypocalcemia: IV may worsen hypocalcemia
  • 3) Not Severe
    • Moderate: 1.0-2.4:
      • Asymptomatic: No treatment required
      • Symptomatic: Oral sodium phosphate/potassium phosphate/PHOS-NAK
        • Phosphate >1.5: 8 mM phosphate q6hr-q8hr x 24hs for total of 24-32mM
        • Phosphate <1.5: 16 mM phosphate q6hr x 24hs for total of 64mM
        • Follow lytes (Ca/Mg/Phos)
  • 4) Severe < 1.0, Symptoms, Malnutrition, lack enteral access:
    • IV Sodium phosphate or IV Potassium phosphate
      • Phosphate >1.5: 15mM over 4 hours
      • Phosphate <1.5: 30mM over 4 hours
    • Follow lytes (Ca/Mg/Phos) - Dipyridamole if low GFR +/- Vitamin D