Can You Test Positive for Multiple Anti-ARS Antibodies?

Testing positive for multiple antisynthetase (anti-ARS) antibodies—such as having both anti-Jo-1 and anti-PL-12 on your lab report—is very uncommon. While it is technically possible, a “double positive” on standard commercial blood tests often warrants confirmation. In many cases, an unexpected second positive result, particularly if the test’s signal is weak, may be a testing artifact rather than a sign of multiple antibodies.

Why Do Tests Show “Double Positives”?

Many standard laboratories use a commercial blood test called a line blot (or line immunoassay). This test checks for many different antibodies at the same time by looking for reactions on a test strip. These tests are convenient, but they can sometimes cross-react or flag an antibody that isn’t really there ^[1]. This is especially common if the test only detected a weak signal strength (meaning the chemical reaction on the test strip was faint) ^[2].

In large medical studies, finding multiple myositis-specific antibodies (the broad family of antibodies that includes anti-ARS, linked to inflammatory muscle diseases) is rare. For example, in one European study of over 1,600 patients with inflammatory myopathy, researchers used a highly specialized testing method and found that only 0.2% of patients had more than one myositis-specific antibody ^[3]. Because of this, medical experts generally consider antisynthetase antibodies to be mutually exclusive, meaning a patient will usually only have one type ^[3].

When researchers looked at a different group of patients whose blood showed multiple antibodies on a standard line blot, those extra results were not confirmed when re-tested using a different, specialist method called immunoprecipitation ^[4].

(Note: Your test might also show a positive for an antibody like anti-Ro52. This is a myositis-associated antibody, which frequently occurs alongside anti-ARS antibodies. This is a common finding and is very different from having two distinct anti-ARS antibodies ^[5].)

What Happens Next?

If your lab report lists two or more antisynthetase antibodies, your doctor may want to verify the results before finalizing your diagnosis ^[6]. An antibody result alone does not diagnose antisynthetase syndrome, determine your disease severity, or dictate your treatment.

To figure out what is really going on, your care team may:

• Check the signal strength: Doctors will look at whether the positive results were marked as “weak” or “strong” on the lab report. Cutoffs differ between labs, but low-positive (weak) results are generally less reliable, particularly when they conflict with your actual symptoms ^[7][8].
• Order a confirmation test: Your doctor might send your blood to a reference laboratory (a specialty lab) for advanced testing. Depending on the antibody, they may use RNA immunoprecipitation (a specialized technique that isolates specific genetic and protein material to confirm antibodies) ^[6][7]. While no test is perfect, these specialist methods are often better at telling apart true antibodies from testing artifacts.
• Look at the big picture: Your doctor will compare your lab results to your physical symptoms. Because line blots can sometimes be misleading, experts recommend diagnosing the condition based on a combination of your symptoms, imaging (like X-rays or CT scans), and confirmed lab work ^[9].

Important Safety Note: Antisynthetase syndrome can cause serious complications, including interstitial lung disease (lung scarring). Never delay medical care while waiting for antibody confirmation. If you experience new or worsening shortness of breath, persistent cough, low oxygen readings, trouble swallowing, or marked muscle weakness, contact your clinical team promptly.