What is being tested?
The serum phosphorus test measures the amount of phosphate in your blood. Normally, only a very small amount of phosphate (in the form of inorganic phosphate) is present in the blood.

In the body, phosphorus exists as a mineral; it 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 phosphorus is found within plasma (the liquid part of blood).

Most phosphorus 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 phosphorus. The body maintains phosphorus/phosphate levels in the blood by regulating how much it absorbs from the intestines and how much it excretes from 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).