Hyperphosphatemia

Definition: Phosphate >4.5mg/dL (1.45 mmol/L)
Causes
- Decreased Renal Excretion (MC)
  - Acute < Chronic Kidney Disease
  - Hypoparathyroidism
- Transcellular Shift from ICF to ECF
  - Rhabdomyolysis
  - Tumor Lysis Syndrome
  - Massive Hemolysis
  - Metabolic Acidosis
  - Insulin Deficiency (DKA) > Lactic Acidosis
  - Fulminant Hepatitis
  - Severe Hyperthermia
- Increased Intake
  - Vitamin D analog use
  - Bisphosphonates
  - Fosphenytoin
  - Phospho-soda Enemas (Fleet)
- Pseudo
  - Hyperbilirubinemia
  - Hyperlipidemia
  - Hemodialysis
  - Hemolyzed sample
  - Liposomal Amphotericin B
  - Paraproteinemia (multiple myeloma)
- Increased Reabsorption
  - Tumoral Calcinosis (FGF23 defect)
Symptoms
- Asymptomatic
  - Related to hypocalcemia
  - Binds calcium and precipitates it in the tissue
- Metastatic calcifications may occur
  - Painful nodules, calcification of soft tissues, pruritis
- Calciphylaxis
Complications
- Renal Osteodystrophy
- Phosphate nephropathy
W/U: Calcium-Phosphate Product
- Predicts risk of calciphylaxis (>70 causes a risk of calciphylaxis)
Treatment
- Should correct within 12-24hr if normal kidney function
- Acute
  - Phosphate restricted diet
  - Stop VitD
  - Increase Renal Excretion
  - Normal Saline (IVF) and Acetazolamide ± Lasix
  - Hemodialysis
    - Increase frequency or duration
- Renal Failure
  - Phosphate restricted diet + oral phosphate binders
  - Sevelamer (Renagel)
    - 800mg TID w/meals, double dose PRN
    - Check med interactions (may absorb some drugs)
    - Preferable in dialysis, avoids mg/ca problems
  - Calcium acetate (PhosLo)
    - 667mg (two tablets TID w/meals)
    - Pts with significant hypocalcemia and Ca-phos product <70
    - Avoid in hypercalcemia, product >66, vitD intoxication
  - Lanthanum
  - Calcium carbonate