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Phosphorus Imbalances

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References:

  1. Saunders Comprehensive Review for the NCLEX-RN Examination, 9th Edition, ISBN 978-032-37-9530-2, by Linda Anne Silvestri, Angela E. Silvestri, and Jessica Grimm (Ch. 8, pp. 88-105)

Hypophosphatemia

Normal Serum Phosphorus Level: 3.0 to 4.5 mg/dL (0.97 to 1.45 mmol/L)

Phosphorus and calcium have a reciprocal relationship in the body; a decrease in phosphorus reflects an increase in calcium and vice versa.

Hypophosphatemia is a serum level of less than 3.0 mg/dL (0.97 mmol/L). It may be caused by:

  1. Insufficient phosphorus intake: malnutrition and starvation
  2. Increased phosphorus excretion: hyperparathyroidism, malignancy, and use of magnesium-based or aluminum hydroxide-based antacid
  3. Intracellular shift: hyperglycemia, respiratory alkalosis

Assessment

Because of the accompanying imbalance of calcium with phosphate imbalances, assessment data is reflective of the opposing imbalance i.e. hypophosphatemia presents with the clinical picture of hypercalcemia.

Hypophosphatemia may be asymptomatic until levels become very low.

Interventions

  • Discontinue medications that contribute to low phosphorus levels.
  • Administer phosphorus orally with a vitamin D supplement. Prepare to administer phosphorus intravenously when serum phosphorus levels fall below 1 mg/dL and when the client experiences critical clinical manifestations. Phosphorus is administered slowly to prevent overcorrection.
  • Assess the renal system before administering phosphorus.
  • Move the client carefully and monitor for signs of pathologic fracture.
  • Increase the intake of phosphorus-containing foods: seeds (sunflower, pumpkin, and squash), whey, cheese, cornmeal, beans, and salt-free nuts (almonds, peanuts).
    • Decrease dietary calcium intake (refer to hypercalcemia).

Hyperphosphatemia

A serum phosphorus level over 4.5 mg/dL (1.45 mmol/L). Most body systems tolerate an elevated phosphorus level well; the problems that arise are the result of the accompanying hypocalcemia that is produced with hyperphosphatemia. Its causes include:

  1. Decreased renal excretion resulting from renal insufficiency
  2. Tumor lysis syndrome
  3. Increased intake of phosphorus, including dietary intake and phosphate-containing laxatives or enemas
  4. Hypoparathyroidism

Assessment

Assessment is the same as for hypocalcemia for reasons stated above.

Interventions

  • Interventions entail the management of hypocalcemia.
  • Administer phosphate-binding medications that increase fecal excretion of phosphorus by binding phosphorus from the food in the gastrointestinal tract.
  • Instruct the client to avoid phosphate-containing medications, including laxatives and enemas.
  • Instruct the client to decrease the intake of food that is high in phosphorus: seeds (sunflower, pumpkin, and squash), whey, cheese, cornmeal, beans, and salt-free nuts (almonds, peanuts).
  • Instruct the client in medication administration: take phosphate-binding medications, emphasizing that they should be taken with meals or immediately after meals.

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