The serum phosphorus test measures the amount of phosphate in the blood.

Phosphorus - serum; HPO4^-2, PO4^-3; Inorganic phosphate; Phosphorus blood test; Serum phosphorus

A blood sample is needed. For information on how this is done, see: Venipuncture

The health care provider may advise you to stop taking drugs that may affect the test.

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.

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 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.

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)

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)

The following can affect phosphorous levels:

• Antacids
• Enemas containing sodium phosphate
• Excess vitamin D supplements
• Glucose through a vein (intravenous)
• Laxatives containing sodium phosphate

Yu SLA. Disorders of magnesium and phosphorous. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 121.