Lab tests for lupus
Many different laboratory tests are used to detect physical changes or conditions in your body that can occur with lupus. Each test result adds more information to the picture your doctor is forming of your illness.
The most common types of tests you may be asked to get are blood and urine tests. It is important to understand these common laboratory tests so you can feel confident as you work with your doctor to better understand your health.
There are several important things to keep in mind when interpreting lab tests:
- Lab work alone usually cannot diagnose lupus. Signs and symptoms of the disease are also important.
- When a positive antinuclear antibody (ANA) test is accompanied by several other clues that doctors look for in diagnosing lupus, it is often a strong indication for doctors to consider lupus.
- It’s common for positive lab tests to come and go over time. If this happens, it’s less likely that you will receive a lupus diagnosis, though still possible.
- It’s very common to get somewhat different results at different labs.
- If your doctor rules out lupus, but you continue to have signs and symptoms, talk to your doctor or seek additional medical help. Whether or not its lupus, it’s important to address your symptoms.
Usually, your doctor will first request a complete blood count (CBC). Your blood is made up of red blood cells (RBCs), white blood cells (WBCs), platelets and serum. The complete blood count measures the levels of each. In cases of lupus, these blood tests may reveal low numbers.
- Red blood cells carry oxygen to all parts of the body.
- White blood cells (lymphocytes and others) help the immune system protect the body against foreign invaders.
- Platelets form in bone marrow; they go to the site of a wound to begin the blood-clotting process.
- Blood serum is the fluid portion of whole blood from which certain substances in the clotting of blood have been removed.
The body uses antibodies to attack and neutralize foreign substances, such as bacteria and viruses. The antibodies your body makes against its own normal cells and tissues play a large role in lupus.
Many of these antibodies are found in a panel or group of tests that are ordered at the same time. The test you will hear about most is called the antinuclear antibodies test, referred to as the ANA test.
97% of people with lupus will test positive for ANA.
Antinuclear antibodies connect or bind to the nucleus or command center of the cell. This process damages and can destroy the cells. While the antinuclear antibody is not a specific test for lupus, it is sensitive and does detect the antibodies that are present in 97 percent of people with the disease.
The ANA can be positive in people with other illnesses or positive in people with no illness, so simply having a positive ANA test does not necessarily mean you have lupus. Test results can also fluctuate in the same person. When a positive ANA is accompanied by several other criteria that doctors look for in diagnosing lupus, it is often a strong indication for doctors to consider lupus.
Doctors trying to diagnose lupus often look for a number of other antibodies as well.
The rate at which your blood begins to clot is important. If it clots too easily, a blood clot (thrombus) could break free and travel through the body. Blood clots can cause damage such as a stroke or miscarriage. If your blood does not clot quickly enough, you could be at risk for excessive bleeding if you are injured.
Some blood tests measure levels of proteins that are not antibodies. The levels of these proteins can alert your doctor that there is inflammation somewhere in your body.
Urine tests are very important because lupus can attack the kidneys -- often without warning signs. The kidneys process your body’s waste materials. Testing a sample of urine (called a “spot urine” test) can reveal problems with the way your kidneys are functioning.
Lupus can attack the kidneys without any warning signs so urine tests are very important.
The most common urine tests look for cell casts (bits of cells that normally would be removed when your blood is filtered through your kidneys) and proteinuria (protein being spilled into your body because your kidneys are not filtering the waste properly). A collection of your urine over a 24-hour period can also give important information.
A biopsy procedure involves removal of a small bit of tissue that the doctor then examines under a microscope. Almost any tissue can be biopsied.
The skin and kidney are the most common sites biopsied in someone who may have lupus.
The results of the biopsy can show the amount of inflammation and any damage being done to the tissue. Further tests on the tissue sample can detect autoimmune antibodies and determine whether lupus or another factor such as infection or medication is responsible.
View our Glossary of Lupus Blood Tests for more details on blood tests for antibodies, proteins and clotting time.