How is it used?
Phosphate testing can be helpful in people who are malnourished or who are being treated for . 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 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 who are on intravenous glucose, levels are monitored frequently as phosphate levels can fall after glucose infusion in severely ill patients.
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 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
0.75- 1.50 mmol/L
0 days to 1 week 1.25–2.85 mmol/L
1 week - 4 weeks 1.50–2.75 mmol/L
4 weeks - 26 weeks 1.45–2.50 mmol/L
26 weeks - 1 year 1.30–2.30 mmol/L
1 year - 4 years 1.10–2.20 mmol/L
4 years - 15 years 0.90–2.00 mmol/L
15 years - 18 years 0.80–1.85 mmol/L
18 years - 20 years 0.75–1.65 mmol/L
The reference intervals shown above are known as a harmonised reference interval. This means that eventually all laboratories in Australia will eventually use this same interval so wherever your sample is tested, the reference interval should be the one shown above. Laboratories are in the process of adopting these harmonised intervals so it is possible that the intervals shown on the report of your results for this test may be slightly different until this change is fully adopted. More information can be found under Reference Intervals – An Overview
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.