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Common CF Tests

Chest X-ray

X-rays use electromagnetic waves to create images of the body. They are usually done while the patient is standing, but can be performed sitting or lying down. The patient will need to hold his or her breath for a short time while the image is being created. Usually both side and front view images are taken. X-rays are painless.

Complete blood count

This is the most common blood test, and measures the three major types of cells in blood: red blood cells, white blood cells, and platelets. The test can check for infections, and can tell if the patient has any side effects from medications.

A small sample is collected from a finger, a heel (in infants), or from a vein. A machine then processes the sample, counting cells, measuring hemoglobin (the part of red blood cells that carries oxygen), and sorting the white blood cells into five subtypes. Results are often available the next day.

Kidney function tests

Kidney function tests measure the health of the kidneys, which filter your blood of wastes. The tests check the amount of waste products passed in urine or left in the blood, and also check the blood's mineral levels. The tests can tell if the kidneys are not functioning as they should, or if medications used to treat CF are affecting the kidneys.

For a blood test, a sample is drawn from a vein??usually from the inside of the elbow or the back of the hand??with a thin needle. For a urine test, the patient urinates in a small jar to collect the sample. In both cases, the samples are sent to a lab for analysis.

Liver function tests

Liver function tests can tell if the liver has been injured by disease or other factors. The liver stores enzymes for digestion, and injury to the liver can release some of these enzymes into the blood. Blood tests measure the level of enzymes in the blood, and can indicate liver damage, or blockage in the ducts around the liver.

Blood is drawn from a vein using a thin needle. The sample is then sent to a laboratory for analysis. Results are often available the next day.

Lung (pulmonary) function tests (PFTs)

This series of breathing tests measures how well the lungs take in and exhale air.. They are usually done in a doctor's office or another medical facility.

Because these tests are hard to do with young children, we wait until a patient is five years old to do PFTs.

Oxygen saturation test

Red blood cells carry oxygen to the organs of the body. When these red blood cells pass through the lungs, they emerge saturated with oxygen. In a patient with lung disease, or another lung condition, not all of these red blood cells leave the lungs carrying oxygen. An oxygen saturation test measures the percentage of red blood cells that carry oxygen. It can tell if a person's lungs aren't working as well as they should.

In some cases, a doctor may use a simple detector that fits on a finger to estimate oxygen saturation. To get a more accurate reading, a doctor will draw blood from an artery in the wrist??where the pulse is normally taken??and then test the blood for its oxygen level. The results of this test are usually available within a half-hour.

Sputum cultures

A sputum culture test analyzes a patient's phlegm or mucus for bacteria that cause lung infections. It can tell if a patient has an infection in his or her lungs.

The patient coughs deeply and spits any phlegm or mucus into a sterile cup. If a patient can't cough up mucus, a throat swab may be performed. The sample is then analyzed in the laboratory. The lab can also test to see which antibiotics will work best against the infection.

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Information on the Dartmouth-Hitchcock Medical Center (DHMC) website:

  • is not provided as medical advice
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DHMC and its affiliated component organizations aspire to deliver consistent high quality medical care to all patients and to continually improve its quality of care as evolving technology and medical knowledge permits.

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