What is being tested ?

Phosphorus is a mineral that combines with other substances to form organic and inorganic phosphate compounds. The terms phosphorus and phosphate are often used interchangeably when talking about testing, but it is the amount of inorganic phosphate in the blood that is measured with a serum phosphorus/phosphate test.

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.

We get the phosphorus we need through the foods we eat. It is found in many foods and is readily absorbed by the digestive tract. Most of the body’s phosphates combine with calcium to help form bones and teeth. Smaller amounts are found in muscle and nerve tissue. The rest is found within cells throughout the body, where they are mainly used to store energy.

Normally, only about 1% of total body phosphates are present in the blood. A wide 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 via the kidneys. Phosphate levels are also affected by the interaction of parathyroid hormone (PTH), calcium, and vitamin D.

Phosphorus deficiencies (hypophosphatemia) may be seen with malnutrition, malabsorption, acid-base imbalances, increased blood calcium, and disorders that affect kidney function. Phosphorus excesses (hyperphosphatemia) may be seen with increased intake of the mineral, low blood calcium, and kidney dysfunction.

Someone with a mild to moderate phosphorus deficiency often does not have any symptoms. With a severe phosphorus deficiency, symptoms may include muscle weakness and confusion. An extreme excess of phosphorus may cause symptoms that are similar to those seen with low calcium, including muscle cramps, confusion, and even seizures.

How to Prepare for the Test ?

Your health care provider may tell you to temporarily stop taking medicines that may affect the test. These medicines include water pills (diuretics), antacids, and laxatives.

DO NOT stop taking any medicine before talking to your provider.

How the Test will Feel ?

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed ?

Phosphorus is a mineral the body needs to build strong bones and teeth. It is also important for nerve signaling and muscle contraction.

This test is ordered to see how much phosphorus is in your blood. Kidney, liver, and certain bone diseases can cause abnormal phosphorus levels.

What Abnormal Results Mean ?

A higher than normal level (hyperphosphatemia) may be due to many different health conditions. Common causes include:

• Diabetic ketoacidosis (a life-threatening condition that may occur in people with diabetes)
• Hypoparathyroidism (parathyroid glands do not make enough of their hormone)
• Kidney failure
• Liver disease
• Too much vitamin D
• Too much phosphate in your diet
• Use of certain medicines such as laxatives that have phosphate in them

A lower than normal level (hypophosphatemia) may be due to:

• Alcoholism
• Hypercalcemia (too much calcium in the body)
• Primary hyperparathyroidism (parathyroid glands make too much of their hormone)
• Too little dietary intake of phosphate
• Very poor nutrition
• Too little vitamin D, resulting in bone problems such as rickets (childhood) or osteomalacia (adult)

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood buildup under the skin)
• Excessive bleeding
• Infection (a slight risk any time the skin is broken)