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Source: Pai, AB. Disorders of Calcium and Phosphorus Homeostasis. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. http://www.accesspharmacy.com/content.aspx?aid=7983818. Accessed August 20, 2012.

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  • Serum phosphorus >4.5 mg/dL (>1.45 mmol/L)

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  • Results from renal failure or endogenous intracellular phosphate release.
    • Tumor lysis syndrome in patients treated for leukemia or lymphoma
    • Hemolysis
    • Rhabdomyolysis

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  • Impaired glomerular filtration rate (GFR) decreases renal tubular reabsorption, leading to phosphate retention.
    • Under normal conditions, 85–90% of filtered phosphate reabsorbed via proximal tubule.
    • Retention of phosphate decreases vitamin D synthesis and induces hypocalcemia, leading to increase in parathyroid hormone (PTH).
  • Administration of oral and rectal phosphate-containing solutions in patients with moderate to several renal insufficiency can result in hyperphosphatemia.

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  • Rare in general population.
  • Incidence: 70% in renal insufficiency or renal failure.
    • Nearly universal finding in patients with stages 4 and 5 chronic kidney disease (CKD).

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  • Acute or chronic renal failure
  • Chemotherapy administration for leukemia or lymphoma

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  • Uncommon in patients with normal kidney function.
  • May present as hypocalcemia and tetany.

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Signs and Symptoms

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  • Acute symptoms include:
    • Gastrointestinal (GI) disturbances
    • Lethargy
    • Obstruction of urinary tract
    • Seizures (rare)
  • Chronic hyperphosphatemia associated with deposition of calcium-phosphate crystals into soft tissues, intrarenal calcification, nephrolithiasis, or obstructive uropathy.
    • Likely to form when product of serum calcium and phosphate concentrations exceeds 50–60 mg2/dL2 (44.8 mmol2/L2).
    • Calciphylaxis: tissue necrosis resulting from precipitation of crystals in arteries, joints, soft tissues, and viscera.

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Means of Confirmation and Diagnosis

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  • Serum phosphorus >4.5 mg/dL (>1.45 mmol/L)

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Laboratory Tests

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  • Metabolic panel
    • Serum phosphorus
    • Serum calcium
  • Parathyroid hormone
  • Vitamin D level

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Differential Diagnosis

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  • Normalize serum phosphate concentrations (or near normal in CKD).
  • Minimize long-term cardiovascular consequences of calcium-phosphate crystal deposition

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  • Most effective way to treat nonemergent hyperphosphatemia: decrease phosphate absorption from GI tract with phosphate binders.
  • Severe symptomatic hyperphosphatemia manifesting as hypocalcemia and tetany treated by IV administration of calcium salts.

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  • Evaluate serum calcium every 4–6 hours during IV calcium infusions.

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  • Increased morbidity and mortality with serum phosphate concentration >6.5 mg/dL (2.10 mmol/L)

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