Primary care anti-cyclic citrullinated protein antibody testing for rheumatoid arthritis reduces unnecessary referrals
George F G Allen, Timothy J McDonald, Stuart Kyle, Nick KeysellAbstract
Objectives
Rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (ACPA) are alternative diagnostic tests for rheumatoid arthritis with similar sensitivity. ACPA has improved specificity compared with RF and so should result in fewer false positives. A retrospective, observational study was conducted following a change in the primary care pathway and test for inflammatory arthritis from RF to ACPA, assessing real-world impact on referrals.
Methods
The primary care test was changed from RF to ACPA as part of a service development in East and North Devon, UK (population 463,000). Data were monitored post-implementation from 1st March to 31st August 2024. ACPA was made available to primary care. GP order-comms automatically redirected requests for RF to ACPA. Local referral guidelines were implemented recommending ACPA to support referral decisions but not for rule-out of inflammatory arthritis. The equivalent six-month period from 2023 when RF was the primary test for inflammatory arthritis was used for comparison.
Results
Positive tests fell from 10.6% with RF to 3.9% with ACPA. This led to 57 (39%) fewer referrals following a positive test. The false positive rate amongst those referred to rheumatology decreased from 59% (91/148) with RF to 32% (29/91) with ACPA. ACPA and RF detected similar numbers of inflammatory arthritis cases with a case yield of 2.1% for both tests.
Conclusion
Replacement of RF with ACPA within a redesigned inflammatory arthritis pathway reduced unnecessary rheumatology referrals. This could help over-subscribed services reduce waiting times and therefore contribute to timely diagnosis of inflammatory arthritis.