While no single test can determine whether a person has lupus, several laboratory tests may help the doctor confirm a diagnosis, or at least rule out other ailments. The most useful tests identify certain autoantibodies that are often present in the blood of lupus patients. A biopsy of the skin or kidneys may also be ordered if those organs are affected. The doctor will look at the entire picture — medical history, symptoms and test results — to determine if you have lupus. Other laboratory tests are used to monitor the progress of the disease once it has been diagnosed.
Guide for Diagnosing Lupus
The American College of Rheumatology provides the following list of symptoms and other measures that doctors can use as a guide to decide if a patient with symptoms has lupus:
- Butterfly-shaped rash over the cheeks — referred to as a malar rash
- Red rash with raised round or oval patches — known as a discoid rash
- Rash on skin exposed to the sun
- Mouth sores: Sores in the mouth or nose lasting from a few days to more than a month
- Arthritis: Tenderness and swelling lasting for a few weeks in two or more joints
- Lung or heart inflammation: Swelling of the tissue lining the lungs (referred to as pleurisy or pleuritis) or the heart (pericarditis), which can cause chest pain when breathing deeply
- Kidney problems: Blood or protein in the urine, or tests that suggest poor kidney function
- Neurologic problems: Seizures, strokes or psychosis (a mental health problem)
- Abnormal blood tests such as:
- Low blood cell counts: Anemia, low white blood cells or low platelets
- Positive antinuclear antibody (ANA) result: Antibodies that can cause the body to begin attacking itself that are present in nearly all lupus patients
- Certain abnormal antibodies: Anti-double-strand DNA (called anti-dsDNA), anti-Smith (referred to as anti-Sm) or antiphospholipid antibodies
Antinuclear Antibody (ANA) Testing
The antinuclear antibody (ANA) test is commonly used to look for autoantibodies that attack components of your cells’ nucleus, or “command” center, triggering autoimmune disorders like lupus. Approximately 95% of people with lupus test positive for ANA, but a number of other, non-lupus causes can trigger a positive ANA, including infections and other autoimmune diseases. The ANA test simply provides another clue for making an accurate diagnosis.
For patients with a positive ANA, more tests are usually performed to check for other antibodies that can help confirm the diagnosis. This series of tests, commonly called an ANA panel, checks for the following antibodies: anti-double-stranded DNA (anti-dsDNA), anti-Smith (anti-Sm), anti-U1RNP, anti-Ro/SSA and anti-La/SSB. Some laboratories also include other antibodies in their panel, including antinucleoprotein, anticentromere or antihistone.
Doctors use these supplemental tests in conjunction with a person’s clinical history to help diagnose or rule out other autoimmune disorders. Specifically, they look for signs of inflammation, active lupus, active autoimmune disease and kidney problems.