Phosphate
At a Glance
Why Get Tested?
To evaluate the level of phosphate in your blood and to aid in the diagnosis of conditions known to cause abnormally high or low levels
When to Get Tested?
As a follow-up to an abnormal calcium level or if you have a kidney disorder.
Sample Required?
A blood sample drawn from a vein in your arm or urine collection (usually a 24-hour sample)
The Test Sample
What is being tested?
The serum phosphate test measures the amount of inorganic phosphate in your blood plasma (the liquid part of blood).
In the body, phosphorus is combined with oxygen to form a variety of phosphates (PO4). Phosphates are vital for energy production, muscle and nerve function, and bone growth. They also play an important role as a buffer, helping to maintain the body’s acid-base balance. About 70% to 80% of the phosphates are combined with calcium to help form bones and teeth, about 10% are found in muscle, and about 1% is in nerve tissue. The rest is found within cells throughout the body, where it is mainly used to store energy; about 1% of total body phosphate is found within plasma.
Most phosphate in the body comes from dietary sources. A variety of foods, such as beans, peas and nuts, cereals, dairy products, eggs, beef, chicken and fish contain small amounts of phosphate. The body maintains phosphate levels in the blood by regulating how much it absorbs from the intestines and how much it excretes or conserves in the kidneys.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. If a timed urine sample is required, you will be asked to save all of your urine over a set time period (usually 24 hours).
The Test
How is it used?
Phosphate testing can be helpful in people who are malnourished or who are being treated for ketoacidosis. Phosphate testing is used to help diagnose and evaluate the severity of conditions and diseases that affect the gastrointestinal tract, interfering with the absorption of phosphate, calcium and magnesium. Testing also can help to diagnose disorders that affect the kidneys, interfering with mineral excretion and conservation, and phosphate levels are carefully monitored in people with kidney failure.
When a person has a known problem that affects their phosphate and/or calcium levels, phosphate levels may be monitored regularly to determine the effectiveness of treatment. Usually, it is done with other tests.
While phosphate levels are most commonly performed on blood samples, fasting or timed urine phosphate measurements also may be used to monitor phosphate elimination by the kidneys.
When is it requested?
A phosphate test is often requested to help interpret abnormal blood calcium levels which may be due to either over or under-activity of the parathyroid glands or due to vitamin D deficiency.
To follow up patients with chronic renal disease as high phosphate found in renal disease contributes to bone disease and calcification of arteries.
In very malnourished people phosphate levels may fall rapidly and require monitoring after they are given food.
In hospitalised patients with a variety of severe illnesses.
Some rare genetic disorders, unusual tumours and some drugs may alter phosphate levels.
What does the test result mean?
Dietary deficiencies in phosphate are rare but may be seen with alcoholism and malnutrition.
Low levels of phosphate (hypophosphataemia) may also be due to or associated with:
- Hypercalcaemia (high levels of calcium)
- Overuse of diuretics (drugs that encourage urination)
- Severe burns
- Diabetic ketoacidosis after treatment
- Chronic antacid use
- Rickets and osteomalacia (due to Vitamin D deficiencies)
Higher than normal levels of phosphate (hyperphosphataemia) may be due to or associated with:
- Kidney failure
- Hypoparathyroidism (underactive parathyroid gland)
- Hypocalcaemia (abnormally low levels of calcium)
- Diabetic ketoacidosis when first seen
- Phosphate supplementation
Is there anything else I should know?
Abnormally high levels of phosphate can lead to organ damage due to calcification (calcium phosphate deposits in organs, such as the kidneys).
Phosphate levels are normally higher in children than in adults because their bones are actively growing. Low phosphate levels in children can inhibit bone growth. Very low levels of phosphate are rare but require swift medical attention.
Soft drinks and pre-packaged food items are high in phosphate content, sometimes as phosphoric acid, which some nutritionists believe contributes to over consumption of phosphorus.
Test results may be affected by the use of enemas and laxatives containing sodium phosphate, excess Vitamin D supplements, and by intravenous glucose administration.
Common Questions
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Article Sources
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