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
As a follow-up to an abnormal calcium concentration, or symptoms of abnormal calcium (fatigue, muscle weakness, muscle cramps), if you have a kidney disorder or uncontrolled diabetes, if you are taking calcium or phosphate supplements, have a nutritional problem or have a suspected hormone imbalance such as Vitamin D or Parathyroid Hormone (PTH).
Overnight fasting may be required for a blood sample; follow any instructions that you are given.
The serum phosphate test measures the amount of inorganic phosphate in your blood plasma (the liquid part of blood). A urine phosphate test measures the amount of inorganic phosphate being excreted by your kidneys.
Phosphate works very closely with calcium within your body and they are frequently measured together.
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, bone growth, and forms the building blocks for cell membranes and your DNA. They also play an important role as a buffer, helping to maintain the body’s acid-base balance. About 85% of the phosphates are combined with calcium to help form bones and teeth and about 15% is found in soft tissues. The rest is found within cells throughout the body, where it is mainly used to store energy; and about 1% of your total body phosphate is found within the 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 significant amounts of phosphate. Phosphate found in animal-based foods is more easily absorbed than that found in plant-based foods. 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 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 digestive system and interfere with the absorption of phosphate, calcium, and magnesium. Testing also can help to diagnose disorders that affect the kidneys and interfere with mineral excretion and conservation 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.
While phosphate levels are most commonly performed on blood samples, fasting or timed urine phosphate measurements also may be used to monitor the removal of phosphate by the kidneys. This is usually through collection of a 24-hour urine sample.
When is it requested?
A phosphate test is often requested to help diagnose diseases and conditions that cause problems with the body’s utilisation of calcium. The test may help in the diagnosis of problems with hormones, such as parathyroid hormone (PTH) and Vitamin D, which functions as a hormone, that regulate the body’s calcium concentration and, to a lesser degree, phosphate.
Although abnormal phosphate levels usually cause no symptoms (with the exception of very low levels), phosphate testing often is performed as a follow-up to an abnormal calcium level and/or related symptoms, such as fatigue, muscle weakness, cramps or bone problems.
Phosphate testing may be requested when symptoms or other tests suggest kidney and/or disorders of the digestive system.
A phosphate test may be requested in people who are treated for malnourishment as this can cause the phosphate level in the blood to fall.
If conditions causing abnormal phosphate and/or calcium levels are found, testing for both may be requested at regular intervals to monitor treatment effectiveness.
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), especially when due to high levels of parathyroid hormone (PTH)
- Overuse of diuretics (drugs that encourage urination)
- Severe burns
- Diabetic ketoacidosis after treatment
- Hypokalaemia (low levels of potassium)
- Chronic antacid use
- Rickets and osteomalacia (due to Vitamin D deficiencies)
- Increased production of insulin
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
- Cardiovascular disease
- Vitamin D overuse
It is important to note that phosphate levels in children are higher than in adults due to active bone growth.
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 young children than in adults because their bones are actively growing. Low phosphate levels in children can inhibit bone growth. Very low levels of phosphate, seen in alcohol use disorder, diabetic ketoacidosis and sepsis, 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 which can be problematic if it is also associated with limited calcium intake.
Test results may be affected by the use of enemas and laxatives containing sodium phosphate, excess Vitamin D supplements, and by intravenous glucose administration.
If there are no symptoms, how will I know if I have an abnormal phosphate level?
Can vegetarians meet their phosphate needs without resorting to meat or dairy products?