How Is Sarcoidosis Diagnosed?
The preliminary diagnosis of sarcoidosis is based on the patient's medical history, routine tests, a physical examination, and a chest X-ray. The doctor confirms the diagnosis of sarcoidosis by eliminating other diseases with similar features.
These include such granulomatous diseases as:
No single test can be relied on for a correct diagnosis of sarcoidosis. An old test used for the diagnosis of sarcoidosis called the Kveim test is no longer in use for several reasons. 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.
The biopsy of a tissue sample of an involved organ is the ultimate test to confirm the diagnosis. Many of the tests that the doctor uses 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. The following are commonly used tests in the evaluation of a patient with sarcoidosis.
The chest X-ray is often helpful to give the doctor a picture of the lungs, heart, as well as 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 lungs can show up on an X-ray. An X-ray can also show which areas of the lung are affected.
Pulmonary function tests
By performing a variety of tests called pulmonary function tests (PFTs), 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 patients with sarcoidosis 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 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 makeup granulomas secrete large amounts of ACE, these enzyme levels are often high in patients with sarcoidosis. Blood ACE levels, however, are not always elevated in people with sarcoidosis, and increased ACE levels can also occur in other illnesses.
This test 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 number 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 indicates an inflammation in the lungs.
Microscopic examination of specimens of lung tissue obtained with a bronchoscope, or of specimens from other tissues, can tell a doctor where granulomas have formed in the body and can provide the ultimate diagnosis.
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.
An instrument called a slit lamp, which permits examination of the inside of the eye, can be used to detect silent eye damage from sarcoidosis.