How is lupus diagnosed?
A diagnosis of lupus is made based on symptoms, a physical examination and blood tests. Tests can help to rule out other conditions.
A number of different blood tests may be used:
- Anti-nuclear antibody (ANA) test
About 95% of people with lupus are ANA positive, but the test can sometimes be positive in people who don't have lupus, so it can’t confirm the diagnosis.
- Anti-double-stranded DNA (anti-dsDNA) antibody test
About 70% of people with lupus have these antibodies. A positive test means that lupus is highly likely as the test is hardly ever positive in people who don't have lupus. The anti-dsDNA level usually goes up when lupus is more active, so repeat tests may be helpful as a means of monitoring your condition and deciding on treatment.
- Anti-Ro antibody test
If you test positive for this autoantibody you may be more likely to get skin rashes and suffer from dry eyes or a dry mouth (Sjögren's syndrome). This autoantibody can pass across the placenta during pregnancy. If you carry the anti-Ro autoantibody and decide to have a baby, your pregnancy will be more closely monitored.
- Antiphospholipid antibody test
A positive test for these autoantibodies may mean an increased risk of miscarriage and developing blood clots.
- Complement level test
Complement refers to a set of proteins in the blood that protect us from infections. Complement levels go down when lupus is more active.
- Erythrocyte sedimentation rate (ESR) test
This test assesses inflammation by measuring how quickly the blood cells settle at the bottom of a test tube. The ESR is often raised in lupus.
- Kidney and liver function tests
These include blood and urine tests, which are carried out regularly so any problems caused by lupus itself or by drug treatment can be recognised and dealt with quickly. A simple urine test can show if there's protein or blood in the urine. This test can help doctors recognise a problem in the kidneys at a very early stage. Further tests, such as kidney filtration tests, may be carried out if necessary. Those with kidney test abnormalities may be asked to have a biopsy which is the most accurate way of finding out how inflamed and damaged the kidneys are.
- Blood cell counts
Haemoglobin, white and red blood cells and platelets are all made in the bone marrow, so blood cell counts can help to show whether the bone marrow is affected, either by the disease or the drugs you're using to treat it.
These tests can also be helpful in monitoring the condition after diagnosis – for example, a combination of higher levels of anti-dsDNA and falling complement levels (often accompanied by a high ESR test) is helpful in predicting a flare-up of lupus. If the C-reactive protein (CRP), another measure of inflammation, is raised, your doctor would also consider whether you have an infection.
A variety of tests are available to check how your heart, lungs, liver and spleen are working. Depending on which organs your doctor thinks may be involved, you may have x-rays, an ultrasound scan, computerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan.
A urine test can show if there's protein or blood in the urine. This can help doctors to recognise a problem in your kidneys at a very early stage. You may need further tests, such as kidney filtration tests.
If you have symptoms such as fever, weight loss and persistent swelling of the lymph glands, your doctor may take a biopsy of lymph gland tissue to rule out cancer, which can also cause these symptoms.