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Lab tests for lupus

Many different laboratory tests are used to detect 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 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 with 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 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.

Common tests used to diagnose lupus

Routine blood tests

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.

See also: How lupus affects the blood

Antibody blood tests

The body uses antibodies to attack and neutralize foreign substances like 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—a group of tests that are ordered at the same time. The test you will hear about most is called the antinuclear antibodies test (the ANA test).

97% of people with lupus will test positive for ANA.

ANA connect or bind to the nucleus or command center of the cell. This process damages and can destroy the cells. The ANA test is not a specific test for lupus. However, it is sensitive and does detect these antibodies 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. For this reason, simply having a positive ANA test does not necessarily mean you have lupus. Test results can also vary in the same person. When a positive ANA is accompanied by several other clues that doctors look for in diagnosing lupus, it is often a strong indication to consider lupus.

Doctors trying to diagnose lupus often look for a number of other antibodies as well.

Blood clotting time

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.

Other blood tests

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

Lupus can attack the kidneys without any warning signs, so urine tests are very important.

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.

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). They also look for protein being spilled into your body because your kidneys are not filtering the waste properly (proteinuria). A collection of your urine over a 24-hour period can also give important information.

Tissue biopsies

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 ANA and determine whether lupus or another factor such as infection or medication is responsible.