CONTENTS
- Rapid Reference 🚀
- Symptoms
- Phosphate level
- Causes of hyperphosphatemia
- Treatment
- Podcast
- Questions & Discussions
- Pitfalls
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:
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.
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.
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.
Please note: The segment on hyperphosphatemia starts at 14:44.
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- 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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