Phosphate, Urine

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Subject: Phosphate, Urine

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Definition

  • Phosphate is a charged particle that contains mineral phosphorus. Extra phosphate is filtered through the kidneys and passes out of the body in the urine.

  • Normal range:

    • Twenty-four–hour urine: 0.4–1.3 g/day

    • Random urine:

      • Male:

    • Less than 40 years: 36–1,770 mg/g creatinine

    • Greater than 40 years: 54–860 mg/g creatinine

      • Female:

    • Less than 40 years: 111–927 mg/g creatinine

    • Greater than 40 years: 105–1,081 mg/g creatinine

Use

  • Evaluation of calcium-to-phosphorus balance

  • Evaluation of nephrolithiasis

Interpretation

Increased In

  • Primary hyperparathyroidism

  • Humoral hypercalcemia of malignancy

  • Vitamin D excess

  • Paget disease

  • Metastatic neoplasm of the bone

  • Fanconi syndrome (renal tubular damage)

  • Nonrenal acidosis (increased phosphate excretion as renal buffer)

Decreased In

  • Hypoparathyroidism

  • Pseudohypoparathyroidism

  • Secondary hyperparathyroidism (renal rickets)

  • Rickets and osteomalacia

  • Parathyroidectomy

Limitations

  • Interpretation of urinary phosphorus excretion is dependent on the clinical situation and should be interpreted in conjunction with the serum phosphorus concentration.

  • There is significant diurnal variation in excretion, with values highest in the afternoon.

  • Urinary excretion depends on diet.

  • Hypophosphatemia with normal serum calcium, high alkaline phosphatase, hypercalciuria, and low urinary phosphorus occurs with osteomalacia from excessive antacid ingestion. Children with thalassemia may have normal phosphorus absorption but high renal phosphaturia, leading to a deficiency of phosphorus.

  • Increasing dietary intake of potassium has been reported to increase serum phosphate concentrations apparently by decreasing renal excretion of phosphate. During the last trimester of pregnancy, there is a sixfold increase in calcium and phosphorus accumulation as the fetus triples its weight.

  • Plasma phosphorus concentrations and increased urinary phosphate may provide a useful means to assess response to phosphate supplements in the premature infants.

 
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