B-182 Clinical Utility of the 14-3-3eta Protein in Seronegative Rheumatoid Arthritis

Abstract

Early identification of rheumatoid arthritis (RA) remains challenging in patients who lack traditional serological markers such as rheumatoid factor (RF) and anti-CCP antibodies. This seronegative population often experiences delays in diagnosis and treatment initiation despite active inflammatory disease. Importantly, emerging epidemiologic data indicates that the global incidence of seronegative RA is increasing representing up to 30% of the RA population, highlighting a growing segment of patients who remain difficult to classify using standard serology. The serum-based protein marker, 14-3-3eta has emerged as a mechanistically relevant biomarker associated with joint damage pathways that may also help uncover inflammatory activity in patients who are seronegative by conventional criteria. The primary objective was to assess the prevalence of 14-3-3eta protein positivity in seronegative rheumatoid arthritis subsets, specifically RF-negative, anti-CCP-negative, and double-negative patient groups. We conducted a pooled analysis of two independent, retrospectively assembled early arthritis cohorts from Netherlands (n=202) and Canada (n=40). Clinical and serological data including RF, anti-CCP, demographic variables, and baseline disease characteristics were available with diagnosis being confirmed by a rheumatologist. 14-3-3eta protein concentrations were measured in banked baseline serum samples using the 14-3-3eta ELISA assay [Augurex Life Sciences]. 14-3-3eta positivity was defined as =0.19 ng/mL. A total of 242 early RA patients were included, of whom 26% were male, with similar sex proportions across anti-CCP-negative, RF-negative, and double-negative groups. Mean age and disease duration were generally comparable across serologic subsets, although patients negative for both RF and anti-CCP had a slightly longer median disease duration (6.35 years). Median 14-3-3eta protein levels were 0.41 ng/mL (IQR 0.07–3.48) in the overall cohort. Median values in the seronegative groups were 0.07 ng/mL (IQR 0.02–0.34) for anti-CCP-negative patients, 0.06 ng/mL (IQR 0.02–0.26) for RF-negative patients, and 0.10 ng/mL (IQR 0.05–5.72) for patients who were negative for both RF and anti-CCP. Importantly, 14-3-3eta protein positivity was observed in 30% of anti CCP-negative patients, 28% of RF-negative patients, and 20% of double-negative patients. These findings demonstrate that the 14-3-3eta protein detects a clinically meaningful proportion of patients who lack conventional autoantibodies, capturing nearly one-third of individuals who are anti-CCP-negative or RF-negative, and 1 in 5 among those negative for both markers, thereby underscoring its complementary role in identifying seronegative RA within early disease. In the context of current diagnostic practice where rheumatologists rely on both anti-CCP and/or RF, these results position the 14-3-3eta as a valuable, complementary biomarker that can enhance early detection, support diagnostic confidence, and potentially accelerate treatment decisions in patients with seronegative presentation.