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Electrolytes & Minerals

Phosphate (Phosphorus)

Normal range 2.5–4.5 mg/dL (0.81–1.45 mmol/L SI). Specimen: Serum.

Also known as: serum phosphorus, PO4, inorganic phosphate.

2.5–4.5 mg/dLCritical: read below

Reference range

Conventionalmg/dL
2.54.5
SImmol/L
0.811.45
SpecimenSerum
Conventional range2.5–4.5 mg/dL
SI range0.81–1.45 mmol/L
Conversion factor×0.323 (conventional → SI)
Critical value< 1.0 mg/dL
PanelElectrolytes & Minerals

Convert any Phosphate (Phosphorus) result between units on the unit converter.

What is the normal range for Phosphate (Phosphorus)?

The standard teaching reference range for Phosphate (Phosphorus) is 2.5–4.5 mg/dL in conventional units, or 0.81–1.45 mmol/L in SI units. This value is measured in serum.

A commonly taught critical (panic) value is < 1.0 mg/dL. Critical results are reported to the provider immediately under your facility's policy.

Source: Adult reference values compiled from Pagana & Pagana, Mosby's Diagnostic and Laboratory Test Reference, and Fischbach & Dunning, A Manual of Laboratory and Diagnostic Tests. Reference ranges vary by laboratory, method, age, sex, and population — always use the range printed on the actual result.

Above the range

Common causes of a high Phosphate (Phosphorus)

  • Renal failure
  • Hypoparathyroidism
  • Tumor lysis syndrome
  • Excess vitamin D

Below the range

Common causes of a low Phosphate (Phosphorus)

  • Refeeding syndrome
  • Hyperparathyroidism
  • DKA treatment
  • Alcohol use disorder

At the bedside

Nursing considerations

  • Phosphate moves inversely to calcium.
  • Watch for severe hypophosphatemia during refeeding — it can cause respiratory failure.

Study aid

Your notes on Phosphate (Phosphorus)

Same panel

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