What is a serum phosphorous test?

Phosphorus is an important element that’s vital to several of the body’s physiological processes. It helps with bone growth, energy storage, and nerve and muscle production. Many foods — especially meat and dairy products — contain phosphorus, so it’s usually easy to get enough of this mineral in your diet.

Your bones and teeth contain most of your body’s phosphorus. However, some phosphorous is in your blood. Your doctor can assess your blood phosphorus level using a serum phosphorus test.

Hyperphosphatemia is when you have too much phosphorus in your blood. Hypophosphatemia is the opposite — having too little phosphorus. Various conditions, including chronic alcohol use disorder and vitamin D deficiency, can cause your blood phosphorus level to become too low.

A serum phosphorus test can determine whether you have high or low phosphorus levels, but it can’t help your doctor diagnose the cause of your condition. Your doctor will need to perform more tests to determine what’s causing abnormal serum phosphorus test results.

Your doctor may order a serum phosphorus test if they suspect that your phosphorus level is too low or too high. Either extreme can lead to health problems.

Symptoms that may indicate your phosphorus level is too low include:

If the level of phosphorus in your blood is too high, you may have deposits of phosphorus combined with calcium in your arteries. Sometimes, these deposits may appear in the muscles. They’re rare and only occur in people with severe calcium absorption or kidney problems. More commonly, excess phosphorus leads to cardiovascular disease or osteoporosis.

Your doctor may also order a serum phosphorus test if you received abnormal results from a blood calcium test. Your body needs to maintain a delicate balance between levels of calcium and phosphorus. An abnormal result on a calcium test may indicate that your phosphorus levels are also atypical.

As with any blood test, there’s a slight risk of bruising, bleeding, or infection at the puncture site. You may also feel lightheaded after having blood drawn.

In rare cases, your vein may swell after blood is drawn. This is known as phlebitis. Applying a warm compress to the site several times a day can ease the swelling.

Many medications can affect your phosphorus levels, including:

Medications that contain sodium phosphate can also affect your phosphorus levels. Be sure to tell your doctor about any medications you’re taking. They may instruct you to temporarily stop using medications that could interfere with your test results.

You don’t typically need to fast before this test. Your doctor will let you know if they want you to fast for any reason.

The test involves a simple blood draw. Your healthcare provider will use a small needle to collect a sample of blood from a vein in your arm or hand. They’ll send the sample to a laboratory for analysis.

Serum phosphorus is measured in milligrams of phosphorus per deciliter of blood (mg/dL). According to Mayo Medical Laboratories, a normal range for adults is generally 2.5 to 4.5 mg/dL.

The normal range varies slightly depending on your age. It’s natural for children to have higher phosphorus levels because they need more of this mineral to help their bones develop.

High phosphorus levels

Excess phosphorus will likely build up in your bloodstream if you have impaired kidney function. Avoiding high-phosphorus foods, such as milk, nuts, beans, and liver, can help lower your phosphorus levels. Sometimes, however, you may need to take medications to prevent your body from absorbing the phosphorus.

Besides reduced kidney function, high phosphorus levels may be due to:

  • certain medications, such as laxatives that contain phosphates
  • dietary problems, such as consuming too much phosphate or vitamin D
  • diabetic ketoacidosis, which occurs when your body runs out of insulin and begins to burn fatty acids instead
  • hypocalcemia, or low serum calcium levels
  • hypoparathyroidism, or impaired parathyroid gland function, which leads to low levels of parathyroid hormone
  • liver disease

Low phosphorus levels

Low phosphorus levels may be due to a range of nutritional problems and medical conditions, including:

Your doctor will analyze your results and discuss them with you. Be sure to ask your doctor any questions you have about your results.