Phosphorus, Blood and Urine


Inorganic phosphorus, phosphate, PO4.

To assist in evaluating multiple body system functions by monitoring phosphorus levels in relation to other electrolytes. Used specifically to evaluate and monitor renal function in at-risk patients, disorders of bone and parathyroid, and kidney stones, and to follow up on acid-base or calcium imbalance.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
Method: Spectrophotometry.

Reference values are dependent on phosphorus and calcium intake. Phosphate excretion exhibits diurnal variation and is significantly higher at night.

AgeConventional UnitsSI Units (Conventional Units × 0.323)
0–5 days4.6–8 mg/dL1.5–2.6 mmol/L
1–3 yr3.9–6.5 mg/dL1.3–2.1 mmol/L
4–6 yr4–5.4 mg/dL1.3–1.7 mmol/L
7–11 yr3.7–5.6 mg/dL1.2–1.8 mmol/L
12–13 yr3.3–5.4 mg/dL1.1–1.7 mmol/L
14–15 yr2.9–5.4 mg/dL0.9–1.7 mmol/L
16–19 yr2.8–4.6 mg/dL0.9–1.5 mmol/L
Adult2.5–4.5 mg/dL0.8–1.4 mmol/L
Values may be slightly decreased in older adults due to dietary insufficiency or the effects of medications and the presence of multiple chronic or acute diseases with or without muted symptoms.

Conventional UnitsSI Units (Conventional Units × 0.0323)
400–1,300 mg/24 hr12.9–42 mmol/24 hr

Critical Findings and Potential InterventionsBlood: Adults

  • Less than 1 mg/dL (SI: Less than 0.3 mmol/L)
  • Greater than 8.9 mg/dL (SI: Greater than 2.9 mmol/L)

Blood: Children

  • Less than 1.3 mg/dL (SI: Less than 0.4 mmol/L)
  • Greater than 8.9 mg/dL (SI: Greater than 2.9 mmol/L)

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Symptoms may be similar to those commonly observed with hypocalcemia to include confusion, muscle cramps, muscle weakness, and seizures. Interventions including IV replacement therapy with sodium or potassium phosphate may be necessary. Close monitoring of both phosphorus and calcium is important during replacement therapy.

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