Diagnosing lupus is a complex process. It's not as simple as diagnosing a broken bone, strep throat, or pregnancy. In these conditions there are simple tests which, if positive, point to a single diagnosis. There is no single diagnostic test for lupus. There is a screening test called the ANA (anti-nuclear antibody) test which is often checked when a doctor suspects lupus.

If the ANA test comes back negative it is considered a normal result, and it is very good evidence against lupus as an explanation for the symptoms. If the ANA test result comes back above the normal range the test is said to be positive. A positive ANA test by itself is not proof of lupus.

Understanding the positive ANA test

What does a positive ANA mean? Unlike a pregnancy test, which if positive generally means only one thing, a positive ANA can mean many things. There are many illnesses and conditions associated with a positive ANA, including rheumatoid arthritis, Sjogren's syndrome, scleroderma, and lupus, as well as infectious diseases such as mononucleosis, subacute bacterial endocarditis, and autoimmune thyroid and liver disease.

Certain medications can cause a positive ANA, and many healthy people with no associated illness or condition have a positive ANA. In fact, about 5% of the general population will have a positive ANA. Thus, at least 95% of the people who have a positive ANA do not have lupus! A positive ANA test can sometimes run in families, even if family members have no evidence of lupus.

The ANA is only a test and, like a high cholesterol value, a positive ANA doesn't necessarily equate having a disease. A positive ANA is only an indicator which points in several possible directions, and indicates that further investigation and analysis may be needed.

How does your doctor use the ANA result?

The doctor will view your ANA and other lab results in light of your history and physical exam to determine if there is sufficient evidence to diagnose a specific illness. None of the connective tissue (joints, tendons, cartilage, collagen, muscles and skin) diseases has specific diagnostic tests. Diagnosis is therefore based on meeting certain criteria for the disease which are based on the symptoms you have had, your physical examination, and your blood tests. In systemic lupus, eleven criteria were developed for research purposes but are frequently used to diagnose lupus.

Usually, physicians do not make a diagnosis of lupus unless they determine that the patient has at least four criteria. If only two or three criteria are met, then there may not be enough evidence to support a diagnosis of lupus. Since not all of the criterion are black and white, a physician may sometimes be uncertain whether a patient meets a particular criterion or not. This adds to the difficulty in diagnosis.

Furthermore, if another disease or condition can explain the presence of the criterion in a patient, then it may not indicate lupus. Therefore, it's possible to meet four criteria, and not have lupus.

Why does it take so long to know "for sure"?

If your ANA is positive and you have many symptoms, your doctor may suspect some kind of connective tissue disease. If at that time there aren't enough symptoms and lab work to satisfy the criteria for any one disease, then it is impossible to specify a particular disease or to confirm a diagnosis.

Lupus tends to develop slowly and evolve gradually over time. Many-or even most-people who have just a few of the criterion for lupus never develop this or any other connective tissue disease, and either improve or continue as they are.

Awaiting a diagnosis can be frustrating. If only one or two criteria are satisfied, it's similar to a picture that's only partially developed. No one looking at that picture can accurately identify it. Nor can they predict if it will develop into anything that can be identified, how long it will take before it is developed enough to identify, or if it will develop further at all!

There is no way to hurry the diagnosis of lupus. The length of time it takes can be highly variable; it may take weeks, months or years. In some cases, it can take as long as 10 years before enough evidence accumulates indicating that it is, in fact lupus.

Learn the signs and symptoms of lupus so that if you develop something new, you can tell your doctor so s/he can determine if you have satisfied enough criteria for a diagnosis.

What about a "borderline" ANA?

All tests have a normal range of values. If a test value is at the upper limit of the normal range or slightly over, it's often referred to as "borderline." The importance of a borderline ANA test depends on the other criterion that are present. A borderline positive ANA will probably be ignored by the doctor if there are only one or two other criterion suggesting lupus, yet could clinch the diagnosis if there are already three or four positive criterion.

Is it possible to have lupus with a negative ANA?

More than 95% of people with systemic lupus have a positive ANA. Only a small percentage have a negative ANA, and many of those have other antibodies (such as anti-phospholipid antibodies, anti-Ro, anti-SSA) or their ANA converted from positive to negative from steroids, cytotoxic medications, or uremia (kidney failure).

How high does my ANA have to get before the doctor says it's lupus?

It is not a question of how high the ANA titre is. Even a very high "titre' ANA by itself is never sufficient to diagnose lupus. Other criteria must be satisfied.

A titre (ti-ter) is the number of times a solution (such as a person's blood) can be diluted before a substance (such as an antibody) can no longer be detected. Thus, an ANA titre of 1:80 means that the blood can be diluted to one in eighty parts and the lab technician can still detect the ANA antibody. The dilutions are usually two-fold, so that the next dilution would be 1:160, and the one after 1:320.

Because normal ranges for ANA titres vary from lab to lab, there is no universal normal range. There is no limit to how high the ANA can go.