1168: Interstitial Lung Disease-Associated Antibody Testing and Positivity Rates in Systemic Autoimmune Rheumatic Diseases from a National Reference Laboratory

Background/Purpose: Interstitial lung disease (ILD) is frequent in systemic autoimmune rheumatic diseases (SARDs) and is associated with poor prognosis. The prevalence of ILD is approximately 52% in systemic sclerosis (SSc), 41% in myositis, 23% in Sjögren’s syndrome (SS), 21.4% in rheumatoid arthritis (RA), 14.5% in systemic lupus erythematosus (SLE), and 56% in overlap syndromes. While early detection of ILD is crucial, diagnostic imaging is typically limited to high-risk patients. Biomarker testing is a cost-effective method for identifying patients at increased risk of ILD. We examined testing and positivity rates of ILD-associated antibodies in patients with SARDs to assess current screening practices.

Methods: We retrospectively reviewed testing for ILD-associated antibodies (Jo-1, PL-7, PL-12, EJ, OJ, SRP, MDA-5, PM/Scl-100, Ku, and SS-A 52kD) in patients with SSc (N = 87,115), idiopathic inflammatory myopathy (IIM, N = 25,496), myositis (N = 110,645), polymyositis (PM, N = 58,619), dermato(poly)myositis (DM, N = 73,568), SS (N = 365,136), RA (N = 3,837,117), SLE (N = 956,740), and overlap syndromes (N = 104,697) from 2021 through 2024. Patients with interstitial pulmonary disease (N = 190,160) were included for reference. Diagnostic labels reflect provider-assigned ICD-10 codes at the time of testing.

Results: PL-7, PL-12, EJ, OJ, SRP, MDA-5, PM/Scl-100, Ku, and SS-A 52kD were tested in less than 1.7% of patients with SSc, SS, RA, SLE, and overlap syndromes (Figure 1). Testing rates for these antibodies ranged from 3.3 – 4.5% in patients with IIM, myositis, or PM, and 5.9 – 6.2% in those with DM. Among patients with SSc, PM/SCL-100 was the second most tested biomarker at 4.2%.

Jo-1 had the highest testing rate across all SARDs, with 6.7 – 9.6% of patients with SSc, IIM, myositis, PM, DM, SS, SLE, and overlap syndromes tested. Jo-1 positivity rates ranged between 0.2 – 1.4% in patients with SSc, IIM, myositis, SS, RA, SLE, and overlap syndromes (Figure 2). Jo-1 was positive in 7.0% of patients with PM and 2.9% of patients with DM.

Despite lower testing rates, positivity rates for SS-A 52kD were consistently higher than Jo-1, ranging from 13.7% in RA to 29.8% in SS. PM/Scl-100 also showed higher positivity rates than Jo-1 in all SARDs except PM, ranging from 3.7% in IIM to 6.7% in overlap syndromes. High positivity rates for Ku and PL-7 were also found in patients with SSc (3.3%, 2.1%), IIM (1.4%, 0.8%), myositis (2.2%, 1.1%), SS (2.1%, 1.5%), RA (1.8%, 1.1%), and overlap syndromes (3.8, 2.2%). MDA-5 also had high positivity rates in patients with IIM (1.4%) and in patients with DM (2.5%).

Conclusion: While Jo-1 was the most frequently tested antibody across all SARDs, positivity rates were low among patients with SSc, SS, RA, SLE, and overlap syndromes. In contrast, markers such as PL-7, Ku, and SS-A 52kD that were tested less frequently had higher positivity rates. MDA-5 had positivity rates comparable to Jo-1 among patients with IIM and DM. These findings suggest that incorporating a broader panel of ILD-associated biomarkers along with Jo-1 may facilitate early detection of ILD in patients with SARDs.