The ANA test for drug-induced lupus

As with systemic lupus, most people with drug-induced lupus develop antinuclear antibodies (ANA), although people with drug-induced lupus caused by quinidine and minocycline often are ANA-negative.

Testing for drug-induced lupus

The ANAs seen in drug-induced lupus are primarily autoantibodies that are able to react with a histone-DNA complex (the major component of the nucleus of all cells). A special laboratory test exists to detect Immunoglobulin G (IgG) antibodies to this histone-DNA complex. This is a sensitive marker for lupus-like disease that is actually brought on by certain drugs.

This specific profile of autoantibodies is also present in most people with systemic lupus, although they usually have additional abnormal antibodies.

Quinidine and hydralazine-induced lupus are exceptions, as only about one-half and one-third, respectively, of people with lupus induced by these drugs have this type of anti-histone antibody.

Should I be periodically tested for ANA?

Although the ANA or anti-histone test can help to confirm a diagnosis of drug-induced lupus, it is not useful to periodically test people who have no symptoms. Most medications with a tendency to induce lupus-like disease also produce (at a much higher frequency) a benign type of anti-histone antibody that doesn't cause any symptoms. Commonly used laboratory tests do not distinguish between benign and disease-associated antibodies. There is no evidence that people who develop only ANA without symptoms are at increased risk for future development of drug-induced lupus symptoms.

In most people who develop drug-induced lupus, the symptoms and positive ANA test appear at about the same time. After discontinuing the causative medication, drug-induced ANA should gradually disappear. (A return to normal can take many months and sometimes years.) 

If the ANA is truly drug-induced, its gradual decline after the medication is discontinued can confirm that the diagnosis was correct.