Background/Purpose: The multianalyte assay panel (MAP) consists of cell-bound complement activation products (CB-CAPs) with lupus and non-lupus autoantibodies combined in an algorithm (Dervieux et al., J Immunol Methods 2017). The test is intended for patients suspected of systemic lupus erythematosus (SLE) to aid the diagnosis. We demonstrated previously that the MAP has clinical utility, as it facilitates SLE diagnosis and treatment decisions (Wallace et al., Lupus Sci & Med 2019). As the number of patients with a positive MAP in that study was small, the present study was conducted to enrich the population of the MAP positive patients and to generate additional data on the clinical utility of MAP.

Methods: Systematic multicenter retrospective review of medical charts was conducted at 12 rheumatology practices in the United States. Adult patients for chart review were selected by Exagen based on the MAP score. To decrease the risk of bias, sets of 5 possible eligible patients were identified for each site. Each set included 2 negative (< -0.1) and 3 positive ( > 0.1): tier-1 positive [MAP(Tier1+)]; tier-2 score > 1 [MAP(High+)]; tier-2 > 0.1 and ≤ 1 [MAP(Low+)]). The cutoff of 1 was based on the likelihood ratio positive of the test. Charts were reviewed at T0 (when the MAP was ordered), T1 (when the results were reviewed) and, if available, T2 (latest visit ≥8 months after T1). Statistical analysis (R) consisted of Kaplan-Meier survival analysis with Cox proportional hazard model and ordered logistic regression, as appropriate.

Results: T0 and T1 were performed for 161 patients. All sites but one reviewed charts as multiples of 5 (5 – 25 patients per site). Charts were reviewed also at T2 for a subset of 90 patients (56%). At T0, physician confidence in SLE diagnosis was low for 93 (58%), moderate for 49 (30%), and high for 19 (12%) patients. Odds of higher confidence in SLE diagnosis increased during the study by 1.74-fold for every unit of increase of the MAP score (p< 0.001). The lupus ICD-10 section (M32) was used as a proxy for diagnosis. Positive MAP led to increased assignment of an SLE code by Cox proportional hazard model (Figure 1). In particular, M32 was assigned to 22 of 65 (34%) MAP positive patients who were anti-dsDNA negative. In addition, MAP negative was superior to anti-dsDNA negative at excluding of an SLE code, as more anti-dsDNA negative than MAP negative patients were at risk of M32 assignment (63% vs 52%) (Figure 1B). Only 3 of the 63 MAP negative patients (5%) were assigned a lupus ICD-10 code during the study, indicating a 95% probability of excluding the SLE diagnosis in MAP negative patients. We also evaluated the use of hydroxychloroquine (HCQ) during the study in the 126 patients who were prescribed HCQ after T0. Kaplan-Meier curves and hazard ratios for initiation of HCQ show that MAP positivity led to HCQ treatment, and that MAP negative was superior to anti-dsDNA negative in avoiding HCQ prescription (58% vs. 45%) (Figure 2).

Conclusion: This study demonstrates that the MAP helps to both diagnose and exclude SLE in patients suspected of the disease and, importantly, informs appropriate treatment decisions in this patient population.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-multianalyte-assay-panel-with-cell-bound-complement-activation-products-demonstrates-clinical-utility-for-the-diagnosis-and-treatment-of-systemic-lupus-erythematosus/