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HYPOPHOSPHATEMIA & HYPERPHOSPHATEMIA
Hypophosphatemia is recognized most often in critically-ill patients, decompensated diabetics, alcoholics or other malnourished persons, and acute infectious or pulmonary disorders.
A decrease in serum phosphate should be distinguished from a decrease in total body storage of phosphate.
Hypophosphatemia may be transient and reflect intracellular shift with minimal clinical consequences.
Most symptoms of acute hyperphosphatemia are due to secondary hypocalcemia.
The significant level of hyperphosphatemia in adults is 5 mg/dL.

Diagnosis

Hypophosphatemia
  • A decrease in serum phosphate should be distinguished from a decrease in total body storage of phosphate (phosphate deficiency)
  • The extracellular fluid contains <5% of total body phosphorus
  • Depending on renal function, serum phosphate may be normal or high in profound intracellular deficiency
  • Serum phosphate may be low even when intracellular phosphate is normal following a sudden movement of extracellular phosphate
Hyperphosphatemia
  • Normal adult range: 2.45-4.5 mg/dL (0.81-1.45 mmol/L)
  • Significant level for hyperphosphatemia in adults: 5mg/dL

Classification

Mild Hypophosphatemia
  • Patient is usually asymptomatic
  • Serum P >0.75-1.0 mmol/L (2.2-3 mg/dL)
Moderate Hypophosphatemia
  • Usually asymptomatic
  • Serum P <0.5-0.7 mmol/L (1.5-2.2 mg/dL)
Severe Hypophosphatemia
  • Patient is usually symptomatic
  • Serum P <0.3-0.5 mmol/L (1-1.5 mg/dL)

Evaluation

  • Hypophosphatemia may be transient & reflect intracellular shift w/ minimal clinical consequences
  • In most cases of intracellular shift of phosphate, serum phosphate normalizes once the cause is managed

Conditions that accelerate intracellular uptake of phosphate

  • Any cause of hyperventilation (eg sepsis, anxiety, pain, etc)
  • Intravenous (IV) glucose administration
  • Insulin therapy
  • Administration of catecholamines & beta-receptor agonists
  • Leukemic blast crisis
  • Administration of erythropoietin or GCS-F
  • Postsurgery or after trauma
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