How to Test for Lupus
Diagnosing lupus is notoriously difficult as lupus presents differently from one person to the next. Lupus may not be immediately evident from diagnostic tests and it tends to have symptoms that can point to other diseases. Getting a diagnosis for this condition is a great accomplishment despite learning that you have lupus. Learn here about how to test for lupus and what’s involved for each clinical and lab test.
How Is Lupus Diagnosed?
The gold standard for diagnosing systemic lupus is matching symptoms and test results to the eleven criteria that were created by the American College of Rheumatology. Your rheumatologist will want to check off at least four criteria on the list before giving you a lupus diagnosis, otherwise, you may receive a diagnosis of undifferentiated connective tissue disease or early lupus.
The criteria for diagnosing lupus must include four or more of these symptoms:
- Malar rash
- Discoid rash
- Oral or nasal ulcers
- Lupus arthritis
- Pleurisy or pericarditis
- Kidney involvement
- Neurological involvement
- Blood issues
- Immune issues
- Positive antinuclear antibody (ANA)
Diagnosing discoid lupus may be a simpler process, depending on your symptoms. Signs of discoid lupus, such as skin lesions or rashes, will prompt a skin biopsy. This biopsy is generally all that’s needed to diagnose discoid lupus.
How to Test for Lupus: What Tests Are Used to Diagnose Lupus?
There are a wide variety of tests that can be used to determine if someone has lupus. Your rheumatologist may take blood or urine samples, use imaging tests, or perform a biopsy to get the information they need.
A positive ANA test means there are antibodies in your body that are attacking normal cells and tissues. It can be an ambiguous test; while almost everyone with active systemic lupus has a positive ANA (around 98 percent), most people with a positive ANA do not have lupus.
However, a positive ANA prompts testing for other antibodies. An ANA panel checks for anti-double-stranded DNA antibody (anti-dsDNA), anti-Smith (anti-Sm), anti-Ro/SSA, and anti-La/SSB.
The anti-dsDNA antibody is more specific to lupus – it’s found in up to 90 percent of people with systemic lupus and only one percent of people without lupus. It’s also associated with lupus nephritis, so a positive result warrants a check of kidney function.
The anti-Sm antibody is extremely specific – almost exclusive – to lupus, but it’s only found in 20 percent of patients. Anti-Ro/SSA and Anti-La/SSB antibodies are associated with lupus and primary Sjogren’s syndrome, so they aren’t very specific but can narrow the field.
Complement proteins are consumed by inflammation, so they are low when lupus is active. They are needed to protect against infections, so low amounts are concerning and mean that a person is immunocompromised.
There are nine groups that are identified using “C” and a number, so you may see C3, C4, or subsets such as C4d on your lab work. Each protein is unique and some are more applicable to lupus than others. Definitely ask your rheumatologist why they have chosen to test for specific complement proteins.
Other Blood Analysis
A complete blood count (CBC) test measures several factors, including the number of red blood cells (RBC), white blood cells (WBC), platelets, and hemoglobin. These test results can reveal a number of things, such as anemia, and they can help determine the effects lupus is having on your body and what treatments you may need to correct things.
You may be tested for erythrocyte sedimentation rate (ESR) and c-reactive protein (CRP) as they are both markers of inflammation (high inflammation levels are common with active lupus). While this is good information to have, there are other reasons why these markers could be elevated. High ESR or CRP are too vague for a lupus diagnosis.
There are also blood tests for checking liver and kidney function. These tests are especially important if your lupus medication(s) may be putting a heavy load on those organs.
Urinalysis to Test for Lupus
Testing urine is important since it’s one of the few ways to determine if lupus is attacking the kidneys. You may be asked for a spot sample or to collect urine over a 24 hour period.
Urinalysis determines if kidneys are functioning well and eliminating waste products from the blood. Tests measure cell casts, protein levels, WBC, and RBC in the urine. Cell casts are pieces of cells that should have been removed by the kidneys and found substantial amounts of protein in the urine also means that the kidneys did not filter them correctly.
Lupus-Related Imaging Tests
Imaging tests will be used if inflammation is occurring in your internal organs or if lupus arthritis could be causing damage to your joints. An X-ray can reveal if there is fluid or inflammation in your lungs and an echocardiogram can check for heart damage.
Biopsy Tests for Lupus
With lupus, biopsies are primarily performed on the skin or kidneys. This means that a doctor will remove a small sample of tissue for analysis.
A kidney biopsy will use a small incision and/or needle while a skin biopsy may simply shave off a small piece of skin instead (in some cases a deeper skin sample will be extracted). Samples will be analyzed for inflammation or antibodies within layers of skin.
Seeking a Lupus Diagnosis
It may be frustrating to learn that testing for lupus is not an easy or precise process, especially if your symptoms or lab results fluctuate over time. It may take several doctors’ appointments for you and your rheumatologist to finally observe or find evidence of multiple lupus symptoms.
Coming to the conclusion that you have lupus means that several criteria have been found that strongly indicate lupus. Yet, even a lupus diagnosis isn’t a sure thing – people have been misdiagnosed with lupus only to find out later it was a different disease-causing their symptoms.
You must continue matching symptoms and lab results to certain criteria in order to maintain a lupus diagnosis and the right treatment plan.