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Lab Manual for UCSF Clinical Laboratories

Lab Manual for SFGH

Internal Resources

PHOSPHORUS, INORGANIC, SERUM

Item Value
Available Stat? Yes
Test code PO4
Performed by? Chemistry
Sendout? no
Price range $
In House Availability Routine: 7 days;
STAT: 24 hours/ 7 days
Principle Phosphomolybdate color complex, read spectrophotometrically.
Interpretation Phosphorus, as phosphate, is distributed throughout the body. Causes of high serum phosphorus include dehydration, hypoparathyroidism, hypervitaminosis D, metastases to bone, sarcoidoisis, pulmonary embolism, renal failure, and diabetes mellitus with ketosis. Low serum phosphorus is found in primary hyperparathyroidism and other causes of serum calcium elevation, sepsis, vitamin D deficiency, renal tubular disorders, chronic hemodiaysis, vomiting, and occasionally with decreased dietary phosphate intake.

Circadian rhythms (high in morning, low in evening), seasonal variations (maximum in May/June, minimum in winter), diet and bed rest can cause fluctuations in phosphate concentrations.
Container type gel tube (gold or green top)
Amount to Collect 2 mL
Sample type Blood
Special instructions Fasting specimen preferred. Hemolyzed serum will not be assayed. Laboratory measures total inorganic phosphorus.
Normal range Serum

14 d – 24 mo 24 mo – 12 yrs 12 yrs – 60 yrs
4.5-6.7 4.5-5.5 2.5-4.5 mg/dL
1.45-2.16 1.45-1.78 0.81-1.45 mmol/L


All values less than 1.0 mg/dL (< 0.32 mmol/L) are considered Critical Values and are called to the physician or patient care unit immediately.
Synonyms Renal Function Panel: METB, ALB, PO4;
Stability Serum stable at 2-8°C for 1 week; frozen for 6 months.
Interferences Many drugs can cause elevation or depression of serum and urine phosphorus, both in vitro and in vivo. If you have questions, contact the Laboratory Medicine Resident in Clinical Chemistry (x65527, or pager (415) 443-2311).

1. Serum decreased: Citrate and oxalate anticoagulants.

2. Serum increased: In vitro hemolysis and delay in separation of serum/plasma from erythrocytes.
References 1. Bayer(TM) Clinical Methods In. Phos (40) B01-4144-01 Advia 1650 Operator's Guide. PN 073-5001-09. Last accessed June 2003. Siemens Medical Solutions Diagnostics, Malvern, PA.

2. Tietz NW ed. Clinical Guide to Laboratory Tests 3rd ed. 1995. WB Saunders, Philadelphia, PA, pg. 486.
CPT coding 84100
Last Updated 6/18/2011 8:23:05 AM
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