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Introduction/Background The rare heterogenous autoimmune disease Juvenile Dermatomyositis (JDM) relies on prognostic tools including myositis specific antibodies (MSA) and myositis associated antibodies (MAA) to guide early treatment and reduce the risks of poor outcome. However, there is an emerging concern regarding the inter-assay validity due to the current lack of a standardised protocol for MSA/MAA screening across healthcare centres. Among available MSA/MAA screening assays, most laboratories prefer using immunoblot over immunoprecipitation, due to its practicality and lower cost. Notably, blotting-based assays were reported to have reduced specificity at detecting certain MSA/MAA subgroups. Description/Method A total of 472 JDM patients recruited via UK Juvenile Dermatomyositis Cohort and Biomarker Study (JDCBS) were included in this study. For immunoprecipitation cohort, the sera of 383 JDM-diagnosed patients were determined at the University of Bath using radio-labelled protein immunoprecipitation, and 140kDa bands were confirmed with ELISA for NXP2 or MDA5. For immunoblot cohort (n = 89), MSA/MAA results were obtained from the patients’ records at the centre of care. The immunoprecipitation group and immunoblot group were investigated for the frequency of each autoantibody subgroup within each cohort. The objective was to determine the sensitivity of each assay in detecting myositis relevant antibodies (MSA/MAA) in the context of JDM. Discussion/Results Overall, the majority of patients were female, and self-identified as white. Specifically, in immunoprecipitation cohort, 70.9% of the patients were female, while 77.1% of the patients self-identified as white. In the immunoblot cohort, 72.7% of the patient were female, while 65.9% self-identified as white. Regarding MSA/MAA status in each cohort, 225 out of 383 (58%) immunoprecipitation samples were positive for at least 1 myositis relevant autoantibody (MSA/MAA). In the immunoblot cohort the proportion was 53% (47 out of 89 samples). Despite the similar gender and ethnicity distribution, the frequencies of autoantibody subgroups varied between two cohorts. In descending order, the 3 most common MSAs detected by immunoprecipitation group were anti-TIF1γ (18.1%), anti-NXP2 (15.8%) and anti-MDA5 (5.9%). On the contrary, anti-MDA5 (15.5%) was the most prevalent autoantibody detected by immunoblot, followed by anti-TIF1γ (11.3%) and anti-NXP2 (9.3%), respectively. The prevalence of more than one myositis relevant autoantibodies detected in a patient was rare in both cohorts. Specifically, when excluding anti-Ro52, a MAA that is not detected with immunoprecipitation, 2.2% of the total patients in immunoblot cohort had more than 1 MSA/MAA. This rate is lower in immunoprecipitation cohort, as only 0.5% of the patients in this cohort were determined to be positive for more than one autoantibody subgroup. When accounting for anti-Ro52 in immunoblot cohort, 7 out of 8 anti-Ro52 positive patients were also positive for anti-MDA5, making up 7.9% of immunoblot cohort. Key learning points/Conclusion The variance between autoantibody frequencies detected by each method suggested that immunoprecipitation and immunoblot assays do not perform equally for all MSA and MAA. The lower detection of anti-TIF1γ in immunoblot is consistent with previous reports. Additionally, a potential reduction of sensitivity in anti-NXP2 detection using immunoblot is observed for the first time. Higher rate of anti-MDA5 in immunoblot cohort might reflect the earlier pre-treatment samples compared to the samples tested in immunoprecipitation cohort, as the titre of anti-MDA5 was reported to decrease with treatment. As MSA/MAA status are interpreted by clinicians to classify JDM patients into homogenous subgroups for more focused treatment plans, the reliability of autoantibody screening process is an issue of interest. Further investigations are necessary to characterise the sensitivity and specificity of each method.

Background/Aims The RNHRD is a tertiary rheumatology centre offering a fast-track GCA assessment service. A 2018 departmental audit highlighted areas of good practice including timely assessment of cases but demonstrated irregularities in follow up processes. COVID-19 dramatically changed the way we could deliver our GCA service. Additionally, we saw increases in referrals, confirmed diagnoses and complex disease in our local population during the pandemic. This prompted us to undertake a service improvement project. Our main aims were to optimise follow up in line with national guidelines, enhance patient safety and improve the patient experience. Methods We undertook a service review, starting by mapping the patients’ journey. Guidelines were reviewed and stakeholders consulted. We identified several areas for improvement including; consultant-led risk stratification of patients, formalised follow up pathways and closer collaborative working with relevant departments. Additionally, we sought to streamline our processes to accommodate the increased COVID-19 workload. Results A risk stratified follow up pathway was created. Patients are stratified at initial review, by consultants, into low and high-risk pathways. Follow up intervals have been standardised in line with BSR guidance. Follow up patients are reviewed in a dedicated clinic; medical and nursing clinics run supervised by a vasculitis specialist. Patients transfer between different clinics, dependent on clinical stability. Patient information provided has been standardised, with increased emphasis on flare management and steroid side effects. In collaboration with patients this is being incorporated into a “GCA patient passport”, offering a consistent information resource for patients and clinicians. The nurse-led patient advice line is used frequently by GCA patients. All GCA queries are now directed to the on-call registrar, to ensure same day responses. Temporal artery ultrasound is well utilised and completed efficiently; 82% of scans between September 2019 and September 2021 occurred within 48 hours of referral. Via close working with vascular ultrasound, we have been able to create dedicated daily ultrasound capacity. Collaborative working with our Ophthalmology department has increased; communication channels between departments have been agreed, and education sessions have been provided. Processes for new GCA patients were streamlined, for example moving location of reviews. This ensured ongoing timely review of new GCA patients despite increased referral numbers. Conclusion COVID-19 had a significant impact on service delivery but provided a catalyst to develop our service. By engaging with stakeholders across disciplines, and reacting to patient feedback, we have been able to institute effective and meaningful change. This process is iterative and we plan further assessment of outcomes including co-morbidities and complications. Further formal patient surveys and development of a GCA expert patient group are underway and will inform further service development. Disclosure B. Mulhearn: None. J. Ellis: None. S. Smith: None. S.L. Tansley: None. S. Skeoch: None.

Objectives In order to address the reliability of commercial assays to identify myositis-specific and -associated autoantibodies, we aimed to compare the results of two commercial immunoassays with the results obtained by protein immunoprecipitation. Methods Autoantibody status was determined using radio-labelled protein immunoprecipitation for patients referred to our laboratory for myositis autoantibody characterization. For each autoantibody of interest, the sera from 25 different patients were analysed by line blot (Euroline Myositis Antigen Profile 4, EuroImmun, Lübeck, Germany) and dot blot (D-Tek BlueDiver, Diagnostic Technology, Belrose, NSW, Australia). Sera from 134 adult healthy controls were analysed. Results Overall commercial assays performed reasonably well, with high agreement (Cohen’s κ >0.8). Notable exceptions were the detection of rarer anti-synthetases with κ Conclusion The assays analysed do not perform well for all myositis-specific and -associated autoantibodies and overall false positives are relatively common. It is crucial that clinicians are aware of the limitations of the methods used by their local laboratory. Results must be interpreted within the clinical context and immunoprecipitation should still be considered in selected cases, such as apparently autoantibody-negative patients where anti-synthetase syndrome is suspected.