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The blood phosphorus test is usually done together with the measurement of calcium, parathyroid hormone or vitamin D and is intended to aid diagnosis and help in the monitoring of diseases involving the kidneys or the gastrointestinal tract.
Phosphorus is a mineral that can be obtained through food and helps in the process of teeth and bones formation, in the functioning of muscles and nerves and energy supply. The adequate levels of phosphorus in the blood of adults is between 2.5 and 4.5 mg/dL, values above or below should be investigated and the cause treated by the doctor.
How it's done
The blood phosphorus test is done by collecting a small amount of blood from an artery in the arm.The collection must be done with the person fasting for at least 4 hours. In addition, it is important to inform the use of medications, such as contraceptives, antibiotics, such as isoniazid, or antihistamines, such as promethazine, for example, as they may interfere with the test result.
The blood collected is sent to the laboratory, where blood phosphorus will be measured. Usually, the doctor requests the blood phosphorus test along with the dosage of calcium, vitamin D and PTH, as these are factors that interfere with the concentration of phosphorus in the blood. Learn more about the PTH exam.
A blood phosphorus test is usually recommended when there are altered levels of calcium in the blood, when problems with the gastrointestinal tract or kidneys are suspected, or when the person has symptoms of hypocalcemia, such as cramps, sweating, weakness and tingling in the mouth, hands and feet. Understand what hypocalcemia is and what it can cause.
The reference values of phosphorus in the blood vary according to age with the laboratory in which the test was performed, and can be:
|0 - 28 days||4, 2 - 9.0 mg/dL|
|28 days to 2 years||3.8 - 6.2 mg/dL|
|2 to 16 years||3.5 - 5.9 mg/dL|
|Over 16 years||2.5 - 4.5 mg/dL|
What does high phosphorus mean
Elevated blood phosphorus, also called hyperphosphatemia, can be due to:
- Hypoparathyroidism, since PTH is found in low concentrations, calcium and phosphorus levels in the blood are not properly regulated, since PTH is responsible for this regulation;
- Kidney failure, since the kidneys are responsible for eliminating excess phosphorus in the urine, thus accumulating in the blood;
- Use of supplements or medications that contain phosphate;
The accumulation of phosphorus in the blood can lead to damage to various organs by calcifications and, thus, cardiovascular problems, for example.
What does low phosphorus mean
Phosphorus in low concentrations in the blood, also called hypophosphatemia, can happen due to:
- Vitamin D deficiency, as this vitamin helps the intestines and kidneys to absorb phosphorus;
- Low dietary phosphorus intake;
- Hypokalemia, which is low concentration of potassium in the blood;
- Hypocalcemia, which is low blood calcium concentration.
Very low levels of phosphorus in the blood of children can interfere with bone growth, so it is important that the child has a balanced diet that involves the consumption of foods rich in phosphorus, such as sardines, pumpkin seeds and almonds, for example. See other foods rich in phosphorus.