Are Antinuclear Antibody Test Results Accurate?

I have a question about some blood results called ANA. I have a very high count — over 600 — and the doctor sent me to a rheumatoid specialist. I have no other symptoms except a high count. I know that it means my immune system is bad, but what does that really mean? Will I get sick very easily with the cold and flu, or does that have nothing to do with the immune system? I am very nervous and confused. The specialist said I have no other symptoms and not to worry about it, so why would my blood count be so high? Have you ever heard of this condition? I am scared I will get really sick soon because of it.

You are referring to the antinuclear antibody test (ANA), a test which is positive often in the disease systemic lupus erythematosus (SLE), or lupus. Your letter brings up two common beliefs about tests and diseases which I want to discuss in this posting.

First is the belief that the examinations and tests that doctors perform to try to diagnose disease are 100 percent accurate; and when positive the tests always indicate that the disease is present. Actually, almost all findings on an examination or results of testing must be interpreted by the doctor in the context of the symptoms presented by the patient, the findings on physical examination, the types of diseases found in the community, the patient’s genetic background, and the degree to which lifestyle and social factors influence the presence or absence of a specific disease. There is no blood test that I can think of offhand where a positive test means that a person has the disease 100 percent of the time, not even the HIV test.

Every test and examination has false positives, meaning that the test shows positive in someone who does not have the disease, and false negatives, meaning that the test shows negative in someone who does have the disease. From knowing the rates of true positives, false positives, true negatives and false negatives, one can calculate the sensitivity of a test and its specificity. The sensitivity of a test is the percentage of people who test positive and actually have the disease. The specificity is the percentage of people who test negative on the test and actually do not have the disease. Ideally one hopes that most tests will have sensitivities and specificities in the high 90 percent range. But even with a test having a sensitivity of 95 percent, one person in 20 will test falsely positive and will not have the disease. Conversely if the specificity of a test is 95 percent, one person in 20 will test falsely negative, and will actually have the disease.

The ANA test has a specificity of around 95 percent, meaning that of 20 people who test negative, 19 actually do not have lupus, but one has tested falsely negative and may have lupus. Its sensitivity is even less, meaning that more than one person out of 20 will test falsely positive but will not have lupus. False positive ANAs are fairly common and occur more frequently in older people, people with other autoimmune diseases, with viral infections, some chronic inflammations, and after taking some medications. Medications notorious for producing positive ANA tests are procainamide, used for some heart arrhythmias, and hydralazine, which used to be frequently prescribed to treat high blood pressure. Positive ANAs may persist for years after someone has taken these drugs.

The other common belief which I want to debunk here is that it is always important, even critical, to treat a disease early in the hopes of producing a cure. This belief probably stems from the emphasis we place on detecting and treating cancer early in its course, and for many cancers, the belief is true; early treatment is much more likely to result in a cure than delay. But this is not the case for many other types of disease, and lupus is one of those. There is no cure for lupus. There are treatments for some of its symptoms and complications, but one would only provide such treatment if the symptom or complication was present and serious. Untreated lupus often progresses, and then remits, and these fluctuations are not predictable. Most of the complications are treated with a cortisone type drug, and there is no evidence that hitting lupus early and hard with such a steroid will in any way change the course of the disease. In fact, in the case of another autoimmune disease, rheumatoid arthritis, it has been shown that steroids do not prevent the long-term complications of the disease, although they do reduce the symptoms.

Steroids of course have many serious long-term side effects, and no doctor would want to prescribe them unless their patient had a serious condition that required it.

I want to reassure you: Listen to your rheumatologist, he’s making a valuable point. You have no symptoms of lupus, this may well have been a false positive test, and there is nothing to be gained by starting any treatment now when you have no symptoms. I also want to mention that, although many patients with active lupus are more susceptible to infections, these tend to be unusual infections — not regular colds or flu — and they are only more susceptible when their disease is active. Since you do not have active lupus, I think you are no more susceptible to infection than any other person of your age.

The information provided on Health Search Online is for educational purposes only and is not a substitute for medical advice, diagnosis or treatment.