- Phosphate level
- Causes of hyperphosphatemia
- Questions & Discussions
- PDF of this chapter (or create customized PDF)
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
- Elevation of phosphate may promote calciphylaxis (the precipitation of calcium phosphate in tissues).
- This may manifest with necrotizing skin ulceration:
- 2.5-5 mg/dL = normal phosphate
- False elevation (pseudohyperphosphatemia) can occur due to:
- hyperglobulinemia (e.g. multiple myeloma)
- hemolyzed specimen
- liposomal amphotercin B
- 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.
causes of hyperphosphatemia
Renal Failure Plus…
- Sustained hyperphosphatemia generally won't occur without renal failure (GFR < 25 ml/min). Normally the kidneys are highly efficient at phosphate excretion.
- However, there is also generally an inciting cause as well:
- Tumor lysis syndrome
- Fulminant hepatitis
- Severe hyperthermia
- Hypothyroidism or hyperthyroidism
- Adrenal insufficiency
- Exogenous phosphate intake (e.g. phosphate-containing laxatives/enemas, TPN)
- Vitamin D toxicity
- Reverse underlying problem.
- Volume resuscitation followed by forced diuresis using acetazolamide +/- loop diuretic.
- Hemodialysis may be required in severe renal dysfunction (especially in tumor lysis syndrome).
- Phosphate-restricted diet
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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questions & discussion
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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
- Hyperphosphatemia (Chris Nickson, LITFL)
Image credits: Calciphylaxis