Lupus - Diagnosing lupus

Systemic lupus erythematosus (SLE) can be difficult to diagnose, as it has similar symptoms to several other, far more common, conditions.

Diagnosis may also be difficult because symptoms can vary greatly from person to person, and they may change over time. For example, there may be periods where your symptoms are not very noticeable, or times when they flare up and become more severe.

For a confident diagnosis of SLE to be made, you will need to have several symptoms of lupus and a number of blood tests may need to be carried out.

Blood tests

Some of the blood tests that may be carried out are described below.

Erythrocyte sedimentation rate (ESR) test

A blood test called the erythrocyte sedimentation rate (ESR) test can be used to determine whether there is any inflammation in your body.

This can be useful in diagnosing SLE because the condition can cause many areas of the body to become inflamed (swell), including the joints and internal organs.

The test works by measuring how long it takes for red blood cells to fall to the bottom of a test tube. The quicker they fall, the more likely it is that there are high levels of inflammation.

Anti-nuclear antibody test

An anti-nuclear antibody test checks whether there is a certain type of antibody cell in your blood, known as the anti-nuclear antibody. Approximately 95% of people with SLE have this antibody.

However, it is possible to have the anti-nuclear antibody without having SLE, so the anti-nuclear antibody test is not a definitive way of testing for the condition. Other blood tests will also be needed to confirm the diagnosis.

Anti-DNA antibody test

An anti-DNA test also checks for a certain type of antibody in your blood, known as the anti-DNA antibody. If you have the anti-DNA antibody, it is highly likely that you have SLE. However, the antibody is only found in around 70% of people with the condition.

The level of anti-DNA antibodies increases when SLE is more active, so during a flare-up of symptoms your reading from this test may be greater than normal.

Complement level test

Complement is a chemical in the blood that forms part of your immune system. The level of this chemical may be tested to check how active your SLE is. The level of complement in your blood decreases when SLE is more active.

Other tests

Once you have been diagnosed with SLE, you will normally need regular monitoring to see how the condition is affecting your body.

If you have SLE it is possible you may develop other conditions, such as kidney problems. Monitoring your condition will allow your doctor to check for these complications and, if necessary, treat them as soon as possible.

You may need to have scans, such as an X-ray, ultrasound scan, magnetic resonance imaging (MRI) scan or a computerised tomography (CT) scan to check whether SLE is affecting your internal organs.

Read more about the complications of lupus.