The phosphorus blood test measures the amount of phosphate in the blood.
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
Your doctor may tell you to temporarily stop taking medicines that may affect the test. These medicines include water pills (diuretics), antacids, and laxatives.
Do not stop taking any medicine before talking to your doctor.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. These soon go away.
Why the Test is Performed
Phosphorus is a mineral the body needs to build strong bones and teeth. It is important for nerve signaling and muscle contraction.
This test is ordered to see how much phosphorus is in your blood. Kidney, liver, and certain bone diseases can cause abnormal phosphorus levels.
Normal values range from 2.4 - 4.1 milligrams per deciliter (mg/dL).
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
- Kidney failure
- Liver disease
- Too much vitamin D
- Too much phosphate in your diet
- Use of certain medications such as phosphate-containing laxatives
Lower than normal levels (hypophosphatemia) may be due to:
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 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)
Phosphorus - serum; HPO4-2, PO4-3; Inorganic phosphate; Serum phosphorus
Pincus MR, Abraham NZ Jr. Interpreting laboratory results. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 8.
Yu SLA. Disorders of magnesium and phosphorous. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 121.
Update Date 10/29/2013
Updated 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, Bethanne Black, and the A.D.A.M. Editorial team.