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Subject: Phosphate, Urine
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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.
Twenty-four–hour urine: 0.4–1.3 g/day
Less than 40 years: 36–1,770 mg/g creatinine
Greater than 40 years: 54–860 mg/g creatinine
Less than 40 years: 111–927 mg/g creatinine
Greater than 40 years: 105–1,081 mg/g creatinine
Evaluation of calcium-to-phosphorus balance
Evaluation of nephrolithiasis
Humoral hypercalcemia of malignancy
Vitamin D excess
Metastatic neoplasm of the bone
Fanconi syndrome (renal tubular damage)
Nonrenal acidosis (increased phosphate excretion as renal buffer)
Secondary hyperparathyroidism (renal rickets)
Rickets and osteomalacia
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.