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Test ID PHOS Phosphorus (Inorganic), Serum

Reporting Name

Phosphorus (Inorganic), S

Useful For

Diagnosis and management of a variety of disorders including bone, parathyroid, and renal disease

Specimen Type


Necessary Information

Patient's age and sex are required.

Specimen Required

Patient Preparation: Patient should fast overnight (12-14 hours)


Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.

Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Frozen (preferred) 365 days
  Refrigerated  7 days

Reference Values


1-4 years: 4.3-5.4 mg/dL

5-13 years: 3.7-5.4 mg/dL

14-15 years: 3.5-5.3 mg/dL

16-17 years: 3.1-4.7 mg/dL

≥18 years: 2.5-4.5 mg/dL

Reference values have not been established for patients that are less than 12 months of age.


1-7 years: 4.3-5.4 mg/dL

8-13 years: 4.0-5.2 mg/dL

14-15 years: 3.5-4.9 mg/dL

16-17 years: 3.1-4.7 mg/dL

≥18 years: 2.5-4.5 mg/dL

Reference values have not been established for patients that are less than 12 months of age.

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Test Classification

This test has been cleared, approved or is exempt by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
PHOS Phosphorus (Inorganic), S 2777-1


Result ID Test Result Name Result LOINC Value
PHOS Phosphorus (Inorganic), S 2777-1

Clinical Information

Of the phosphorus contained in the body, 88% is localized in bone in the form of hydroxyapatite. The remainder is involved in intermediary carbohydrate metabolism and in physiologically important substances such as phospholipids, nucleic acids, and adenosine triphosphate (ATP). Phosphorus occurs in blood in the form of inorganic phosphate and organically bound phosphoric acid. The small amount of extracellular organic phosphorus is found exclusively in the form of phospholipids. Serum contains approximately 2.5 to 4.5 mg/dL of inorganic phosphate (the fraction measure in routine biochemical assays). Serum phosphate concentrations are dependent on meals and variation in the secretion of hormones such as parathyroid hormone (PTH) and may vary widely.


Hypophosphatemia may have 4 general causes: shift of phosphate from extracellular to intracellular, renal phosphate wasting, loss from the gastrointestinal tract, and loss from intracellular stores.


Hyperphosphatemia is usually secondary to an inability of the kidneys to excrete phosphate. Other factors may relate to increased intake or a shift of phosphate from the tissues into the extracellular fluid.


Hypophosphatemia is relatively common in hospitalized patients. Serum concentrations of phosphate between 1.5 and 2.4 mg/dL may be consider moderately decreased and are not usually associated with clinical signs and symptoms. Levels below 1.5 mg/dL may result in muscle weakness, hemolysis of red cells, coma, and bone deformity and impaired growth.


The most acute problem associated with rapid elevations of serum phosphate levels is hypocalcemia with tetany, seizures, and hypotension. Soft tissue calcification is also an important long-term effect of high phosphorus levels.


Phosphorus levels below 1.0 mg/dL are potentially life-threatening and are considered a critical value in the Mayo Health System.

Clinical Reference

1. Tietz Textbook of Clinical Chemistry. Edited by Burtis and Ashwood. WB Saunders Co, Philadelphia, PA, 1994

2. Yu GC, Lee DBN: Clinical disorders of phosphorus metabolism. West J Med 1987;147:569-576

Analytic Time

Same day/1 day

Method Name

Photometric, Ammonium Molybdate


If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.