Test Overview

A phosphate test measures the amount of
phosphate in a blood sample. Phosphate is a charged
particle (ion) that contains the
mineral phosphorus. The body needs phosphorus to build
and repair bones and teeth, help nerves function, and make muscles contract.
Most (about 85%) of the phosphorus contained in phosphate is found in bones.
The rest of it is stored in tissues throughout the body.

The
kidneys help control the amount of phosphate in the
blood. Extra phosphate is filtered by the kidneys and passes out of the body in
the urine. A high level of phosphate in the blood is usually caused by a kidney
problem.

The amount of phosphate in the blood affects the level of
calcium in the blood. Calcium and phosphate in the
body react in opposite ways: as blood calcium levels rise, phosphate levels
fall. A hormone called parathyroid hormone (PTH) regulates the levels of calcium and phosphorus in your blood. When the phosphorus level is measured, a vitamin D level, and sometimes a PTH level, is measured at the same time. Vitamin D is needed for your body to take in phosphate.

The relation between calcium and phosphate may be disrupted by some
diseases or infections. For this reason, phosphate and calcium levels are
usually measured at the same time.

Why It Is Done

A test to measure phosphate in blood may be done to:

  • Check phosphate levels if you have kidney
    disease or bone disease.
  • Help find problems with certain glands,
    such as the
    parathyroid glands.
  • Find a reason for abnormal vitamin D levels.

How To Prepare

Many medicines can change the results of this test. Be sure to tell
your doctor about all the nonprescription and prescription medicines you
take, including vitamin D supplements.

Talk to your doctor about any concerns you have regarding the need
for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form (What is a PDF document?).

How It Is Done

Blood test

The health professional taking a sample of your blood
will:

  • Wrap an elastic band around your upper arm to
    stop the flow of blood. This makes the veins below the band larger so it is
    easier to put a needle into the vein.
  • Clean the needle site with
    alcohol.
  • Put the needle into the vein. More than one needle stick
    may be needed.
  • Attach a tube to the needle to fill it with
    blood.
  • Remove the band from your arm when enough blood is
    collected.
  • Put a gauze pad or cotton ball over the needle site as
    the needle is removed.
  • Put pressure on the site and then put on a
    bandage.

Heel stick

In a newborn baby, the blood sample is usually taken from the
heel (heel stick).

For a heel stick blood sample, several drops of blood are
collected from the heel of your baby. The skin of the heel is first cleaned
with alcohol and then punctured with a small sterile lancet. Several drops of
blood are collected in a small tube. When enough blood has been collected, a
gauze pad or cotton ball is placed over the puncture site. Pressure is
maintained on the puncture site briefly, and then a small bandage is usually
put on.

How It Feels

Blood test

You may feel nothing at all from the needle puncture, or you may
feel a brief sting or pinch as the needle goes through the skin. Some people
feel a stinging pain while the needle is in the vein. But many people do
not feel any pain (or have only minor discomfort) once the needle is positioned
in the vein. The amount of pain you feel depends on the skill of the health
professional drawing your blood, the condition of your veins, and your
sensitivity to pain.

Heel stick

A brief pain, like a sting or a pinch, is usually felt when the
lancet punctures the skin. Your baby may feel a little discomfort with the skin
puncture.

Risks

Blood test

There is very little risk of complications from having blood
drawn from a vein. You may develop a small bruise at the puncture site. You can
reduce the risk of bruising by keeping pressure on the site for several minutes
after the needle is withdrawn.

In rare cases, the vein may become inflamed after the blood
sample is taken. This condition is called phlebitis and is usually treated by
applying a warm compress several times daily.

Heel stick

There is very little risk of a serious problem developing from a
heel stick. A small bruise may develop at the puncture site.

Continued bleeding can be a problem for babies with bleeding
disorders. There is a possibility that a bleeding problem may be discovered
while collecting the blood for this test.

Results

A phosphate test measures the amount of
phosphate in a blood sample. Phosphate is a charged
particle (ion) that contains the
mineral phosphorus. Phosphate levels are usually
higher in children than in adults because of the active bone growth occurring
in children.

Results are usually available in 1 to 2 hours.

Normal

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Phosphate in bloodfootnote 1
Milligrams per deciliter (mg/dL) Millimoles per liter (mmol/L)
Adults:

2.7-4.5

0.87-1.45

Children:

4.5-5.5

1.45-1.78

Newborns:

4.5-9.0

1.45-2.91

High values

High phosphate levels may be caused by:

Low values

Low phosphate levels may be caused by:

  • Hyperparathyroidism, certain bone diseases (such as
    osteomalacia), lack of vitamin D, or
    some kidney or liver diseases.
  • Severe malnutrition or
    starvation.
  • A condition such as
    sprue that prevents the intestines from absorbing
    nutrients properly.
  • Alcohol dependence.
  • High calcium
    levels.
  • Some types of tumors.

What Affects the Test

Results from a blood phosphate test may be affected by:

  • Using some medicines that can decrease phosphate
    levels, such as acetazolamide and epinephrine. A large
    infusion of sugar (glucose) that causes insulin levels to increase can also
    decrease phosphate levels.

What To Think About

References

Citations

  1. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

Credits

ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Kathleen Romito, MD – Family Medicine
Specialist Medical Reviewer Alan C. Dalkin, MD – Endocrinology

Current as ofMay 3, 2017