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Blood Phosphate Level

Blood Phosphate Level

Definition
Purpose
Precautions
Description
Preparation
Aftercare
Risks
Results

Definition

Phosphate is a mineral that is found in abundance in the body. About 85% of the body’s phosphate is in bone. Phosphate is also a major component of teeth. Phosphate is involved in producing and repairing bone, as well as in the functioning of both nerves and muscles. Phosphate is used to help produce energy for the cell, as well as in the production of DNA.

Calcium and phosphate are both present in the blood, but in inverse proportions. In other words, higher blood calcium levels result in lower blood phosphate levels; lower blood calcium levels result in higher blood phosphate levels. Excess phosphate in the blood, beyond what is needed for proper functioning, is processed by the kidneys and excreted in the urine.

Phosphate acquired through the diet, in yeast, beans, lentils, grains, peanuts, and almonds. As with calcium, vitamin D is required for the proper absorption of phosphate. Excess phosphate in the body is excreted through the urine and the stool.

Purpose

A blood phosphate level is usually drawn as part of a larger panel of electrolytes. Other measurements in the electrolyte panel include calcium, chloride, potassium, and sodium. A blood phosphate level is usually checked when there are concerns about the functioning of the patient’s kidneys, to monitor patients who are on renal dialysis, in the presence of bone disease, to diagnose disorders of the parathyroid glands, to monitor intestinal disorders that affect nutrient absorption, and as part of the monitoring performed when a diabetic patient goes into ketoacidosis.

KEY TERMS

Acromegaly— A condition in which an overactive pituitary gland pumps out an excess amount of growth hormone.

Dialysis— A procedure that takes over the blood filtering capacity normally provided by the kidneys. Includes both hemodialysis (in which blood passes out of the body through a tube running from a blood vessel in the arm to a special dialysis machine) and peritoneal dialysis (in which a special catheter is implanted in the abdominal cavity, a special dialysis solution is infused into the abdomen, waste products from the body enter the solution, and the solution is then drained back out of the abdominal cavity.

Hyperphosphatemia— Elevated blood phosphate levels.

Hypophosphatemia— Low blood phosphate levels.

Ketoacidosis— A condition brought on by extremely elevated blood glucose, resulting in a life-threatening metabolic acidosis.

Parathyroid— Several small glands located behind the thyroid glands in the mid-neck. The parathyroid glands secrete parathyroid hormone, which is highly involved in the chemical equilibrium of calcium and phosphate throughout the body.

Precautions

The test results can be affected by alcohol, as well as some medications, such as steroids, androgen hormones, vitamin D supplements, and enemas containing phosphate, antacids containing aluminum, insulin, acetazolamide, epinephrine, or large quantities of glucose. Patients who are taking anticoagulant medications should inform their healthcare practitioner since this may increase their chance of bleeding or bruising after a blood test.

Description

This test requires blood to be drawn from a vein (usually one in the forearm), generally by a nurse or phlebotomist (an individual who has been trained to draw blood). A tourniquet is applied to the arm above the area where the needle stick will be performed. The site of the needle stick is cleaned with antiseptic, and the needle is inserted. The blood is collected in vacuum tubes. After collection, the needle is withdrawn, and pressure is kept on the blood draw site to stop any bleeding and decrease bruising. A bandage is then applied.

Preparation

There are no restrictions on diet or physical activity, either before or after the blood test.

Aftercare

As with any blood tests, discomfort, bruising, and/or a very small amount of bleeding is common at the puncture site. Immediately after the needle is withdrawn, it is helpful to put pressure on the puncture site until the bleeding has stopped. This decreases the chance of significant bruising. Warm packs may relieve minor discomfort. Some individuals may feel briefly woozy after a blood test, and they should be encouraged to lie down and rest until they feel better.

Risks

Basic blood tests, such as blood phosphate levels, do not carry any significant risks, other than slight bruising and the chance of brief dizziness.

Results

In adults, a normal blood phosphate level is 3.0–4.5 milligrams per deciliter (mg/dL) or 0.97-1.45 millimoles per liter (mmol/L). Children and infants normally have higher blood phosphate levels because their bodies are in a phase involving rapid bone growth. In children a normal blood phosphate level is 4.5-6.5 mg/dL or 1.45-2.10 mmol/L. In infants, a normal blood phosphate level is 4.3-9.3 mg/dL or 1.4-3.0 mmol/L.

High levels

High blood phosphate levels may be due to:

  • kidney disease;
  • poorly functioning parathyroid glands (hypoparathyroidism);
  • acromegaly (a condition in which the pituitary is overactive, and secretes too much growth hormone;
  • rhabdomyolysis (a condition in which muscle is broken down, releasing phosphate, among other substances);
  • bone diseases, including recent fractured bones;
  • diabetic ketoacidosis (a condition in which the blood glucose becomes extremely elevated);
  • excess vitamin D;
  • shortage of magnesium; or
  • pregnancy.

Low levels

Low blood phosphate levels may be due to:

  • overactive parthyroid glands (hyperparathyroidism);
  • kidney disease;
  • liver disease;
  • malnutrition or outright starvation;
  • burns;
  • severe alcoholism;
  • excess blood calcium (hypercalcemia);
  • vitamin D deficiency;
  • bone disorders, such as osteomalacia (an adult type of rickets in which the bones becomes softer due to a vitamin D deficiency); or
  • intestinal disorders that result in poor absorption of nutrients.

Resources

BOOKS

Brenner, B. M., and F. C. Rector, eds. Brenner & Rector’s The Kidney, 7th ed. Philadelphia: Saunders, 2004.

Goldman L., D. Ausiello, eds. Cecil Textbook of Internal Medicine, 23rd ed. Philadelphia: Saunders, 2007.

McPherson R. A., and M. R. Pincus, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods, 21st ed. Philadelphia: Saunders, 2006.

OTHER

Medical Encyclopedia. Medline Plus. U.S. National Library of Medicine and the National Institutes of Health. January 2, 2008. http://www.nlm.nih.gov/medlineplus/encyclopedia.html (February 10, 2008).

ORGANIZATIONS

American Association for Clinical Chemistry, 1850 K Street, NW, Suite 625, Washington, DC, 20006, (800) 892-1400, http://www.aacc.org.

Rosalyn Carson-DeWitt, M.D.

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