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Phosphorus - blood
Definition
The serum phosphorus test measures the amount of phosphate in the blood.
Alternative Names
Phosphorus - serum; HPO4-2, PO4-3; Inorganic phosphate; Phosphorus blood test; Serum phosphorus
How the test is performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
The health care provider may advise you to stop taking drugs that may affect the test.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is performed to see how much phosphorus in your blood. Kidney, liver, and certain bone diseases can cause abnormal phosphorus levels.
Normal Values
Normal values range from 2.4 - 4.1 milligrams per deciliter (mg/dL).
The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Higher than normal levels (hyperphosphatemia) may be due to many different health conditions. Common causes include:
- Diabetic ketoacidosis
- Hypoparathyroidism
- Too much phosphate in your diet
- Liver disease
- Renal failure
- Too much vitamin D
- Use of certain medications such as phosphate-containing laxatives
Lower than normal levels (hypophosphatemia) may be due to:
- Alcoholism
- Hypercalcemia
- Hyperparathyroidism
- Very poor nutrition
- Too little dietary intake of phosphate
- Vitamin D, resulting in rickets (childhood) or osteomalacia (adult)
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Special considerations
The following can affect phosphorous levels:
- Antacids
- Enemas containing sodium phosphate
- Excess vitamin D supplements
- Glucose through a vein (intravenous)
- Laxatives containing sodium phosphate
References
Yu SLA. Disorders of magnesium and phosphorous. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 121.
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
