How is sarcoidosis diagnosed?
Because the symptoms and laboratory findings associated with sarcoidosis can occur in other diseases, there is no single test that can diagnose it. However, the classic sign of the disease is the formation of granulomas (abnormal masses or nodules consisting of inflamed tissue) in one or more of the major organs of the body. Sarcoidosis-related granulomas are not different from granulomas that occur in other diseases. As a result, a complete physical exam and medical history – including occupational history, medication history, and environmental exposures – must be made before concluding that the illness is, in fact, sarcoidosis.
What types of tests are used to diagnose sarcoidosis?
The main tools your doctor will use to diagnose sarcoidosis include:
- Chest X-rays: This test provides a picture of the lungs, heart and surrounding lymph nodes, and reveals where infection-fighting white blood cells have formed – often, the first indication of sarcoidosis. An X-ray can also show how much of the lungs are affected by the disease. Chest X-ray findings fall into one of the following 5 patterns described in the chart below. It is important to know that these X-ray patterns do not represent disease stages (in other words, they are not the sequential steps in the disease course). The categories simply allow doctors to classify the "types of disease."
Chest X-ray patterns
0 = Normal chest X-ray
I = Bilateral hilar lymphadenopathy (BHL): the X-ray shows an equal degree of enlargement of lymph nodes at the “root” of both sides of the lungs. This is a common presentation of sarcoidosis.
II = BHL plus pulmonary infiltrations: the X-ray shows a disease process as described above with expansion into and throughout additional lung tissue.
III = Pulmonary infiltration only (without BHL): the X-ray shows a disease process that is spread throughout the lung tissue (with no enlargement of lymph nodes).
IV = Pulmonary fibrosis: the X-ray shows small lung fields, scarring, and “retraction” of both hila (the area at the “root” of the lungs). This type of disease is the most severe or permanent form of the disease.
- Bronchoscopy: Bronchoscopy involves passing a small tube (bronchoscope) down the trachea (windpipe) and into the bronchial tubes (airways) of the lungs. The purpose of this test is to inspect the bronchial tubes and to extract a biopsy (a small tissue sample) to look for granulomas, and to rule out infection. Bronchoscopy is a safe, low risk, outpatient procedure that provides your doctors with a good chance of making an accurate diagnosis. To prepare for this test, you will be asked not to eat or drink anything by mouth for 8 hours before the exam. Prior to the start of the exam, medications will be given to you to help you relax. Because these medications can make you groggy, an adult who can drive you home must accompany you. You will not be allowed to drive. The procedure usually lasts 15 to 45 minutes, with several additional hours for recovery. Your doctor may perform a bronchoalveolar lavage (washing out the air sacs), biopsies of the air sacs or airway wall using a forceps, or biopsy of a lymph node using a needle that is inserted through the bronchoscope. Guidance of the needle with an ultrasound probe attached to the bronchoscope (endobronchial ultrasound or EBUS) can almost always lead to a diagnosis of sarcoidosis when it is present.
- CT scan: This test is another form of X-ray that provides an even more detailed look at the lungs and lymph glands than that provided by a routine chest X-ray. This test does not hurt and simply involves lying on a table for about 10 minutes.
- Mediastinoscopy: This is a surgical procedure that involves a small incision at the base of the neck through which an instrument is passed to biopsy lymph nodes in the chest cavity. This test is performed under general anesthesia in the operating room of a hospital and takes 1 to 2 hours (same day procedure). The need for mediastinoscopy to make a diagnosis has gone down dramatically as EBUS-guided biopsies have become widespread.
- Pulmonary function (breathing) tests: These tests measure how well the lungs are working (expanding and exchanging oxygen and carbon dioxide in the blood). One pulmonary function test uses a device called a spirometer. This device records the changes in air flow as a person inhales and exhales, as well as the overall volume of air exhaled. The development of granulomas and fibrosis of the lung tissue stiffen the lung tissue and destroy the air sacs, making it more difficult for the lungs to perform these tasks.
- Other biopsies: In addition to the bronchoscopic biopsy or lymph node biopsy by mediastinoscopy, tissue samples can be taken from any other involved site including other lymph nodes, skin, and other sites to determine where granulomas have formed.
- Blood tests: Blood analyses evaluate the number and types of blood cells and blood proteins in the body, and how well the cells are functioning. They also track increases in calcium levels and abnormal liver function that sometimes accompany sarcoidosis. One blood test measures a substance called angiotensin-converting enzyme (ACE), which is secreted in large amounts by cells that make up granulomas. ACE levels, however, are not always high in sarcoidosis patients, and increased ACE levels can also show up in other illnesses. In short, there is no specific blood test to diagnose sarcoidosis. A newer blood test that is sometimes more useful than ACE is a measurement of the soluble interleukin 2 receptor levels (sIL2R).
- Pulse oximetry: This test measures the amount of oxygen in the blood by way of a sensor attached to a patient’s finger. If the oxygen level is low, your doctor may recommend the use of supplemental oxygen.
- Electrocardiogram (EKG or ECG): This is a routine office test that checks the electrical activity of the heart. For this test, electrodes with adhesive pads are attached to the skin of the patient’s chest, arms, and legs. The EKG machine creates a picture, on graph paper, of the electrical impulses traveling through your heart. This screening test helps doctors detect several abnormalities in the heart rhythm.
- PET Scan: In this test, a small amount of radioactive material called F-fluorodeoxyglucose is injected into a vein. This substance collects in the areas where the granulomas have collected. A scanner then detects and records the location and amount of inflammation in the body. This scan will detect inflammation created by conditions other than sarcoidosis so it will be used in combination with other testing.
- Gallium scanning: In this procedure, the radioactive chemical gallium-67 is injected into a vein. The gallium collects in inflamed body tissue. A scan of the body then indicates which tissues and how much tissue is affected. The scan will reveal any type of inflammation occurring in the body, however, and does not necessarily mean the patient has sarcoidosis. Because of this test’s limitations, it is not commonly performed.
- Purified protein derivative: This is a type of skin test that is used to help establish prior exposure or infection with tuberculosis (TB). Since TB is sometimes confused with sarcoidosis, this simple test is frequently performed. In sarcoidosis, this skin test is usually negative or non-reactive.
- Slit-lamp examination: This examination looks at the inside of the eye and is used to detect eye-related problems caused by sarcoidosis.