Glossary of Lupus Blood Tests

Most people with lupus have antinuclear antibodies (ANAs) in their blood. But a positive ANA test doesn’t always mean lupus. The test can be positive in people with other autoimmune illnesses — conditions that cause your immune system to damage healthy cells and tissue — and in healthy people.

Half of the people with lupus have anti-dsDNA. But lupus can still be present even if these antibodies are not found. These antibodies are also used as monitoring tests of lupus activity. 

Histone is a protein that helps organize DNA into a cell. Antibodies to histone are sometimes found in people with systemic lupus erythematosus (SLE). But more often, histones are found in people with drug-induced lupus. This type of lupus is caused by certain medicines, and usually goes away after the medicine is stopped. 

These antibodies can accelerate clot formation. That can lead to problems like blood clots in the legs or lungs, stroke, heart attack, or miscarriage. Nearly 3 in every 10 people with lupus will test positive for aPLs. But not everyone who has aPLs will have problems caused by them. 

These antibodies target proteins that help control chemical activities of the cell. Anti-RNPs are found with many autoimmune conditions. They’re found in very high levels in people whose symptoms combine features of several diseases, including lupus.

Antibodies to these proteins are often found in people with Sjögren’s disease. Anti-Ro60 will be found in people with a form of cutaneous (skin) lupus that causes a sun-sensitive rash. It’s especially important to test for Ro60 and La antibodies if you’re pregnant, because both antibodies can cause neonatal lupus in the infant. 

These antibodies are found in up to 4 out of every 10 people who have lupus. When antibodies to Sm are found, it almost always means you have lupus.

This test can help diagnose lupus and other types of connective tissue diseases (CTDs). It uses a panel of biomarkers in an algorithm to calculate a person’s likelihood that they have a CTD. , It can help doctors confirm or rule out several different diseases at once, which can help speed up the process of diagnosis. It can also help predict someone’s future risk of developing CTD.

Complements are a group of proteins that strengthen the body’s immune reactions and protect against infections. People with inflammation caused by active lupus often have low complement levels. The two most common complement tests for lupus are C3 and C4. Different complement tests can give doctors different information. They might measure the overall function of complement in the blood  or they might look for signs of active lupus, or information that can help “rule in” lupus and “rule out” other conditions. 

CRP is produced by the liver. High levels of CRP in your blood may mean you have inflammation cause by lupus.

ESR is another test for inflammation. It measures the amount of a protein that makes red blood cells clump together. ESR is usually high in people with active lupus. But it can also be high because of other reasons, like an infection.