Serum Phosphorus

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

Serum phosphorus is often done to assess or monitor parathyroid or calcium abnormalities. Phosphorus exists in both an organic and inorganic form. This tests measures the inorganic form of phosphorus which is often combined with calcium within the skeleton; however approximately 15% exists in the blood as a phosphate salt. Organic phosphorus part of the energy pathways of the body and is used to produce nucleic acids and enzymes. Inorganic phosphorus contributes to electrical and acid-base homeostasis.[1],[2]

Patient Preparation

  • Factors which can cause increased levels
  • Laxatives or enemas containing sodium phosphate, hemolysis of blood
  • Factors which can cause decreased levels
  • a high carbohydrate meal can cause phosphorous to enter the cell with glucose causing decreased serum levels

Clinical Implications

Phosphorus levels are determined by calcium metabolism, parathyroid hormone (PTH), renal excretion, and, to a lesser degree, intestinal absorption.[1]

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 2.5-4.5 mg/dL 0.81-1.45 mmol/L
Optimal Range 3.0-4.0 mg/dL 0.97-1.29 mmol/L
Alarm Ranges < 2.0 or > 5.0 mg/dL < 0.65 or > 1.61 mmol/L

High levels indicate:

  • Parathyroid hypofunction
  • Bone growth (Children) and bone repair
  • Diet-excessive phosphate consumption
  • Renal insufficiency and dysfunction
  • Other conditions: edema, ovarian hyperfunction, excess intake of Vitamin D, sarcoidosis, bone neoplasm, diabetes, liver dysfunction, portal dysfunction, portal cirrhosis, excessive intake of antacids

Low levels indicate:

Associated Tests


  1. 1.0 1.1 Pagana Kathleen D, Pagana Timothy J, (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain