Laboratory tests used in the diagnosis of Lupus

The first laboratory test ever devised was the LE (lupus erythematosus) cell test. When the test is repeated many times, it iseventually positive in about 90 percent of the people with systemic lupus. Unfortunately, the LE cell test is not specific for systemic lupus (despite the official-sounding name). The test can also be positive in up to 20 percent of the people with rheumatoid arthritis, in some patients with other rheumatic conditions like Sjogren's syndrome or scleroderma, in patients with liver disease, and in persons taking certain drugs (such as procainamide, hydralazine, and others).

The immunofluorescent antinuclear antibody (ANA, or FANA) test is more specific for lupus than the LE cell prep test. The ANA test is positive in virtually all people with systemic lupus, and is the best diagnostic test for systemic lupus currently available. If the test is negative, the patient will likely not have systemic lupus. On the other hand, a positive ANA, by itself, is not diagnostic of lupus since the test may also be positive in:

1. individuals with other connective tissue diseases;
2. individuals without symptoms;
3. patients being treated with certain drugs, including procainamide, hydralazine, isoniazid, and chlorpromazine;
4. individuals with conditions other than lupus, such as scleroderma, rheumatoid arthritis, infectious mononucleosis and other chronic infectious diseases such as lepromatous leprosy, subacute bacterial endocarditis, malaria, etc., and liver disease.
   

ANA test reports include a titer. The titer indicates how many times an individual's blood must be diluted to get a sample free of anti-nuclear antibodies. Thus, a titer of 1:640 shows a greater concentration of anti-nuclear antibodies than a titer of 1:320 or 1:160. The titer is always highest in people with lupus. Patients with active lupus have ANA tests that are very high in titer.

Laboratory tests which measure complement levels in the blood are also of some value. Complement is a blood protein that, with antibodies, destroys bacteria. It is an "amplifier" of immune function. If the total blood complement level is low, or the C3 or C4 complement values are low, and the person also has a positive ANA, some weight is added to the diagnosis of lupus. Low C3 and C4 complement levels in individuals with positive ANA test results may also be indicative of lupus kidney disease.

Physicians will sometimes also perform skin biopsies of both the individual's rashes and his or her normal skin. These biopsies can help diagnose systemic lupus in about 75 percent of patients.

The interpretation of all these positive or negative tests, and their relationship to symptoms, is frequently difficult. A test may be positive one time and negative another time, reflecting the relative activity of the disease or other variables. When questions cannot be resolved, consult an expert in lupus.

When someone has many symptoms and signs of lupus and has positive tests for lupus, physicians have little problem making a correct diagnosis and initiating treatment. However, a more common problem occurs when an individual has vague, seemingly unrelated symptoms of achy joints, fever, fatigue, or pains. Some doctors may think the person is neurotic. Others may try different drugs in the hope of suppressing the symptoms. Fortunately, with growing awareness of lupus, an increasing number of physicians will consider the possibility of lupus in the diagnosis.

A patient can help the doctor by being open and honest. A healthy dialogue between patient and doctor results in better medical care, not only for people with lupus, but for anyone seeking medical treatment.

To whom should a person go for a diagnosis of lupus? Most individuals usually seek the help of their family doctor first, and this is often sufficient. However, when unresolved questions arise or complications develop, another opinion from a specialist may be advisable. The choice of specialist depends on the problem. For example, you would see a nephrologist for a kidney problem or a dermatologist for a skin problem. Most often, a rheumatologist or clinical immunologist specializing in lupus is recommended. Referrals can be made through your family doctor, the local medical society, or the local affiliate chapter.