Phosphorus blood test
The phosphorus blood test measures the amount of phosphate in the blood.
Phosphorus - serum; HPO4-2; PO4-3; Inorganic phosphate; Serum phosphorus
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
Your health care provider 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 provider.
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. This soon goes away.
Why the Test is Performed
Phosphorus is a mineral the body needs to build strong bones and teeth. It is also 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:
- Adults: 2.8 to 4.5 mg/dL
- Children: 4.0 to 7.0 mg/dL
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
A higher than normal level (hyperphosphatemia) may be due to many different health conditions. Common causes include:
- Diabetic ketoacidosis (life-threatening condition that may occur in people with diabetes)
- Hypoparathyroidism (parathyroid glands do not make enough of their hormone)
- Kidney failure
- Liver disease
- Too much vitamin D
- Too much phosphate in your diet
- Use of certain medicines such as laxatives that have phosphate in them
A lower than normal level (hypophosphatemia) may be due to:
- Hypercalcemia (too much calcium in the body)
- Primary hyperparathyroidism (parathyroid glands make too much of their hormone)
- Too little dietary intake of phosphate
- Very poor nutrition
- Too little vitamin D, resulting in bone problems such as rickets (childhood) or osteomalacia (adult)
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
- Fainting or feeling lightheaded
- Multiple punctures to locate veins
- Hematoma (blood buildup under the skin)
- Excessive bleeding
- Infection (a slight risk any time the skin is broken)
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Kliegman RM, Stanton BF, St. Geme JW, Schor NF. Electrolyte and acid-base disorders. In: Kliegman RM, Stanton BF, St. Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 55.
Chonchol M, Smogorzewski MJ, Stubbs JR, Yu ASL. Disorders of calcium, magnesium, and phosphate balance. In: Yu ASL, Chertow GM, Luyckx VA, Marsden PA, Skorecki K, Taal MW, eds. Brenner and Rector's The Kidney. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 18.