Diagnostic Utility of Antibodies to Extractable Nuclear Antigens in the Absence of Positive Antinuclear Antibodies

TL;DR

This study finds that testing for antibodies to nuclear antigens is not useful when antinuclear antibody tests are negative.

Contribution

The study is the first to evaluate the diagnostic value of isolated positive ENA tests in ANA-negative patients over time.

Findings

Only 4.5% of ANA-negative patients tested positive for ENA.

Just 5.6% of ENA-positive, ANA-negative patients received a new autoimmune diagnosis.

Most positive ENA results in ANA-negative cases are likely false positives.

Abstract

Objective: The antinuclear antibody (ANA) test by indirect immunofluorescence (IFA) is highly sensitive for systemic autoimmune rheumatic diseases (SARD), however, its specificity is low, necessitating additional testing for antibodies to extractable nuclear antigens (ENA). The American College of Rheumatology recommends screening with the ANA by IFA but advises against testing further if the ANA is negative. This is based primarily upon consensus opinion and a limited number of studies. This study further investigates the utility of an isolated positive ENA in patients with negative ANA followed over time and evaluated by a rheumatologist, the first such study to do so.

Methods: All patients aged ≥18 years seen at the University of Cincinnati Medical Center who tested negative for ANA and positive for ENA within a 30-day window between April 2015 and April 2024 and were evaluated by a rheumatologist on at least one occasion constituted the study population. Clinical diagnoses were established by board-certified rheumatologists and independently verified through electronic medical record review by a second rheumatologist.

Results: Among 4,462 patients undergoing ANA testing with subsequent rheumatology evaluation, 1,594 had concurrent ENA testing. Of these, 72 patients (4.5%) exhibited ENA positivity despite negative ANA results. Only four of the 72 ANA-negative, ENA-positive patients (5.6%) received a new diagnosis of a SARD.

Conclusions: The utility of testing for ENA when the ANA by IFA is negative is low. The vast majority of positive tests are false positives that lead to additional testing at additional costs.

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