Sarcoidosis (cont.)
What do laboratory tests show?
No single test can be relied on for a correct diagnosis
of sarcoidosis. X-rays and blood tests are usually the first procedures the
doctor will order. Pulmonary function tests often provide clues to
diagnosis. Other tests may also be used, some more often than others.
Many of the tests that the doctor calls on to help diagnose
sarcoidosis can also help the doctor follow the progress of the disease and
determine whether the sarcoidosis is getting better or worse.
Chest x-ray
The chest x-ray is often helpful to give the doctor a
picture of the lungs, heart, as well as the surrounding tissues containing lymph
nodes (where infection-fighting white blood cells form) and give the first
indication of sarcoidosis. For example, a swelling of the lymph
glands between the two lungs can show up on an x-ray. An x-ray can
also show which areas of the lung are affected.
Pulmonary function test
By performing a variety of tests called pulmonary function tests (PFT), the doctor can find out how well the lungs are doing their job
of expanding and exchanging oxygen and carbon dioxide with the
blood. The lungs of sarcoidosis patients cannot handle these tasks as well
as they should; this is because granulomas and fibrosis of lung tissue
decrease
lung capacity and disturb the normal flow of gases between the
lungs and
the blood. One PFT procedure calls for the patient to breathe
into a
machine, called a spirometer. It is a mechanical device that
records
changes in the lung size as air is inhaled and exhaled, as well
as the
time it takes the patient to do this.
Blood test
Blood analyses can evaluate the number and types of blood
cells in the body and how well the cells are functioning. They can also measure
the levels of various blood proteins known to be involved in immunological
activities, and they can show increases in serum calcium levels
and
abnormal liver function that often accompany sarcoidosis.
Blood tests can measure a blood substance called angiotensin
converting enzyme (ACE). Because the cells that make up
granulomas secrete
large amounts of ACE, the enzyme levels are often high in
patients with
sarcoidosis. ACE levels, however, are not always high in
sarcoidosis
patients, and increased ACE levels can also occur in other
illnesses.
Bronchoalveolar lavage
This uses an instrument called a bronchoscope—a long,
narrow tube with a
light at the end—to wash out, or lavage, cells and other
materials from
inside the lungs. This wash fluid is then examined for the
amount of
various cells and other substances that reflect inflammation
and immune
activity in the lungs. A high number of white blood cells in
this fluid
usually indicate an inflammation in the lungs.
Biopsy
Microscopic examination of specimens of lung tissue obtained
with a
bronchoscope, or of specimens of other tissues, can tell a
doctor where
granulomas have formed in the body and can provide the ultimate diagnosis.
Gallium scanning
In this procedure, the doctor injects the radioactive chemical
element gallium-67 into the patient's vein. The gallium collects at places in
the body affected by sarcoidosis and other inflammatory conditions. Two days
after the injection, the body is scanned for radioactivity. Increases in gallium
uptake at any site in the body indicate that inflammatory activity has developed
at the site and give an idea of which tissue, and how much tissue, has been
affected. However, since any type of inflammation causes gallium uptake, a
positive gallium scan does not
necessarily mean
that the patient has sarcoidosis.
Kveim test
This test involves injecting a standardized preparation of
sarcoid
tissue material into the skin. On the one hand, a unique lump
formed at
the point of injection is considered positive for sarcoidosis.
On the
other hand, the test result is not always positive even if the
patient has
sarcoidosis.
The Kveim test is not used often in the United States
because no test material has been approved for sale by the U.S. Food and Drug
Administration. However, a few hospitals and clinics may have
some
standardized test preparation prepared privately for their own
use.
Slit-lamp examination
An instrument called a slit lamp, which permits examination of
the
inside of the eye, can be used to detect silent damage from
sarcoidosis.
Next: How is sarcoidosis treated? »
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