Understanding Your Lupus Lab Work

Lupus causes the immune system to attack normal cells throughout your body. It is often difficult to diagnose. For example, there is no single blood test to determine if you have lupus.^1,2

But laboratory testing (also called lab work or labs) and your symptoms can help doctors make the diagnosis. Test results are also used to guide and monitor treatment. Here, we discuss the basics of common lab work for people with lupus.^1,2

How results are reported

Lab work for people with lupus may include tests on blood, urine, and tissue samples. Each test provides information about how lupus is affecting your body. Making sense of your lab results before talking with your doctor can be challenging. Here are some general terms to help you understand your results.^3,4

Positive, negative, or inconclusive

• Positive means the condition or level being tested for was found. This is generally an “abnormal” result.^3,4
• Negative means the results do not show the condition or level being tested for. This is generally a “normal” result.^3,4
• Inconclusive means the results are unclear and further testing may be needed.^3,4

Reference range (normal value)

The reference range, or normal value, includes the high and low results considered normal. Normal values are based on results from large groups of healthy people. These ranges can vary slightly from one testing facility to another.^3,4

If your test results are higher or lower than the normal value, it may indicate a problem. But a result outside the normal range is not always cause for alarm. Talk to your doctor to see what your results mean.^3,4

Lab work to diagnose lupus

Doctors use lab results in combination with other information from your history and physical exam to diagnose lupus. Here are common lab tests doctors use when diagnosing lupus:^5,6

• Antibody tests: Antibodies are substances the immune system makes to fight illness. When certain antibodies show up on blood tests, that can mean your immune system is mistakenly harming healthy cells (“autoimmune activity”). In addition to those listed below, there are additional antibody tests that your doctor may order to rule out problems other than lupus.^2,7-9 Interpreting the results of these tests is complex. It is best to discuss your results with your doctor.
• Anti-double-stranded DNA: Specific for (unique to) lupus. About 30 percent of people with lupus have a positive test. A positive test may indicate more severe lupus, especially affecting the kidneys.^2,7-9
• Anti-histone: Can be positive with lupus but not specific.^2,7-9
• Anti-La/SSB and anti-Ro/SSA: Can be found with lupus and other autoimmune diseases. Up to 15 percent of healthy people can also have low levels. People with lupus who plan to become pregnant should be checked for these antibodies. The antibodies have been linked to health problems in babies.^2,7-9
• Antinuclear antibody: Of people with lupus, 98 percent test positive for antinuclear antibody. But you can have a positive test without having lupus.^2,7-9
• Antiphospholipid (aPL): Include anti-cardiolipin (aCL), anti-Beta-2 glycoprotein-1, and lupus anticoagulant (LAC). About half of people with lupus have positive aPL tests. Positive aPL tests, especially LAC and aCL, are linked to increased risk of blood clots. People without lupus can also have positive aPL tests.^2,7-9
• Anti-Smith: Specific for lupus. Positive in about 20 percent of people with lupus.^2,7-9
• Anti-U1RNP: Found in about 25 percent of people with lupus, but can also be positive with other autoimmune diseases.^2,7-9
• Complement proteins: These proteins are part of the immune system and include C3 and C4. Low levels indicate inflammation and can be seen with lupus.^2,7-9
• Skin or kidney biopsy: Effects of lupus on the skin and kidney can be seen in tissue samples.⁵

General lab work

In addition to tests used to diagnose lupus, some tests help doctors monitor your overall health and manage treatment. These tests give doctors clues about how lupus is affecting your body.^2,6

Complete blood count: Your blood is made up of red blood cells, white blood cells, platelets, and serum. Low levels are abnormal and are common in people with lupus.^2,5

C-reactive protein: This measures inflammation. An elevated level is abnormal, but it is not specific to lupus.²

Erythrocyte sedimentation rate (ESR): This measures the activity of red blood cells. An abnormal result can indicate inflammation in the body. ESR is not specific for lupus. It can be elevated in cases of autoimmune disease, infection, and cancer.^2,10

Kidney and liver function tests: A complete metabolic panel (CMP) includes several blood tests to monitor kidney and liver function. The CMP also includes additional tests to check your overall health.^2,8

• Kidney function – measured by sodium, potassium, chloride, creatinine, and blood urea nitrogen
• Liver function – measured by aspartate transaminase, alanine transaminase, alkaline phosphatase, and bilirubin

Urinalysis: A sample of urine (pee) is checked for signs of kidney damage. Protein or blood in the urine is abnormal and may occur if lupus is affecting your kidneys.^2,5

Talk with your doctor about your lab results. If you don’t understand something, ask for more information.