The observation that lupus may affect more than one member of the same family has raised the possibility that the tendency to develop lupus may be inherited. Having such a tendency, however, does not predict that a relative will develop lupus. Only about 10% of people with lupus have a close relative with the disease.
How Is Lupus Diagnosed?
Lupus is diagnosed when a person has several features of the disease (including symptoms, findings on examination, and blood test abnormalities). The American College of Rheumatology has devised criteria to assist doctors in making the correct diagnosis of lupus. A person should have at least four of the following 11 criteria, either at the same time or one after the other, to be classified as having lupus. These criteria include:
- Malar rash, a "butterfly" rash that appears on the cheeks.
- Discoid rash, red, scaly patches on the skin that cause scarring.
- Photosensitivity, a skin reaction or sensitivity to sunlight.
- Oral ulcers (open mouth sores).
- Arthritis, pain, inflammation, or swelling of the joints.
- Kidney disorder, either excess protein in the urine (proteinuria) or red blood cells in the urine.
- Neurological disorder, seizures, or psychosis.
- Inflammation of the lining around the lungs (pleuritis) or of the lining around the heart (pericarditis)
- Blood disorder, either low red blood cell count (anemia), low white blood cell count (leukopenia), decrease in lymphocytes (lymphopenia), or decrease in blood platelets (thrombocytopenia).
- Immunologic disorder, including the presence of certain cells or autoantibodies, or a false-positive test result for syphilis.
- Abnormal blood work, a positive antinuclear antibody (ANA) test result from blood work.
What Is an Antinuclear Antibody Test
An antinuclear antibody (ANA) test is a sensitive screening tool used to detect autoimmune diseases, including lupus. Antinuclear antibodies (ANAs) are antibodies that are directed against certain structures within a cell's nucleus (thus, antinuclear antibody). ANAs are found in particular patterns in people with autoimmune diseases (those in which a person's immune system works against his or her own body).
An ANA test is done on a sample of a person's blood. The test determines the strength of the antibodies by measuring how many times the person's blood must be diluted to get a sample that is free of antibodies.