CONTENTS

• Rapid Reference 🚀
• Symptoms
• Phosphate level
• Causes of hyperphosphatemia
• Treatment
• Podcast
• Questions & Discussions
• Pitfalls

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rapid reference

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symptoms

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Hyperphosphatemia itself is generally asymptomatic.  However, hyperphosphatemia may indirectly cause symptoms in two ways.

more common: symptomatic hypocalcemia

• Phosphate binds calcium, which can lead to hypocalcemia.
• Hypocalcemia may cause symptoms, for example:
  • Paresthesias (tingling around mouth, hands).
  • Muscle cramping, weakness, laryngospasm.
  • Anxiety, confusion, seizure.
  • Hypotension, ventricular arrhythmias.
• More on clinical findings in hypocalcemia: 📖

rare: calciphylaxis

• Elevation of phosphate may promote calciphylaxis (the precipitation of calcium phosphate in tissues).
• This may manifest with necrotizing skin ulceration:

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phosphate level

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phosphate level

• 2.5-5 mg/dL = normal phosphate.
• Pseudohyperphosphatemia (false elevation) may result from:
  • Hyperlipidemia.
  • Hyperbilirubinemia.
  • Hyperglobulinemia (e.g. multiple myeloma).
  • Hemolyzed specimen.
  • Liposomal amphotericin B.

calcium-phosphate product

• More important than the phosphate level alone, as this predicts the risk of calciphylaxis (precipitation of calcium phosphate in tissues).
• Defined as calcium level multiplied by phosphate level (with both measured in mg/dL).
• Calcium-phosphate product above 70 mg*mg/dL*dL causes a risk of calciphylaxis.

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causes of hyperphosphatemia

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Renal Failure Plus…

• Normally the kidneys are highly efficient at phosphate excretion. Sustained hyperphosphatemia generally won't occur without renal failure (GFR <25 ml/min).
• However, there is also generally an inciting cause as well:

…tissue necrosis

• Tumor lysis syndrome.
• Rhabdomyolysis.
• Hemolysis.
• Fulminant hepatitis.
• Severe hyperthermia.

…endocrinopathy

• Hypoparathyroidism.
• Hypothyroidism or hyperthyroidism.
• Adrenal insufficiency.

…medications

• Exogenous phosphate intake (e.g. phosphate-containing laxatives/enemas, TPN).
• Vitamin D toxicity.
• Bisphosphonates.
• Fosphenytoin.

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treatment

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acute treatment

• Reverse underlying problem.
• Phosphate-restricted diet.
• Volume resuscitation, followed by forced diuresis using acetazolamide +/- loop diuretic.
• Hemodialysis may be required in severe renal dysfunction (especially in tumor lysis syndrome).

chronic treatment: phos-restricted diet plus phosphate binder

• Calcium acetate (Phoslo™️) 💊
  • 667 mg tablets, start with two tablets TID with meals
  • Can be useful in patients with hypocalcemia.
  • ⚠️ Avoid in hypercalcemia, vitamin D intoxication, Ca-Phos product > 66.
• Sevelamer (Renagel™️) 💊
  • Start at 800 mg PO TID with meals, double dose if needed.
  • Nonabsorbable resin avoids problems with Mg, Ca (may be preferable for patients on dialysis).
  • ⚠️ May adsorb some drugs.

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podcast

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Please note: The segment on hyperphosphatemia starts at 14:44.

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questions & discussion

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To keep this page small and fast, questions & discussion about this post can be found on another page here.

• Patients with hyperphosphatemia may have low calcium levels. There may therefore be a temptation to give intravenous calcium to restore the calcium level. However, this would be dangerous because it could increase the calcium-phosphate product, thereby causing calciphylaxis

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