24th February 2025

Investigation of RA

RA is essentially a clinical diagnosis; however, specific auto-antibodies are useful investigations which can confirm or refute the provisional diagnosis: rheumatoid factor (RF; 69% sensitivity, 85% specificity) and anti-cyclic citrullinated peptide (anti-CCP; 67% sensitivity, 95% specificity). If both RF and anti-CCP are positive, there is a 100% positive predictive value for a diagnosis of RA. Interestingly, a diagnosis of seronegative RA can be made without positive auto-antibodies if the clinical features and other investigations are suggestive of RA. This can be challenging as other diagnoses, such as spondyloarthritis (including psoriatic arthritis), need to be considered and are often later thought to be the actual diagnosis.

Inflammatory markers such as CRP and ESR are often useful adjuncts and can be repeated to assess the response to therapy. An FBC can be useful to look at the haemoglobin (anaemia of chronic disease) and white cell count (inflammation/infection), and LFTs and U&Es to get a baseline (as these are required prior to and for ongoing monitoring of most DMARDs). X-rays (joint erosion and fusion; see Figure 5) and ultrasound (synovitis and effusions) are useful in assessing painful joints, and bone density scanning (DEXA, dual-energy X-ray absorptiometry) to assess bone mineral health (particularly in the context of repeated corticosteroid courses).

Left: Image source: Wikimedia Commons (2017). Rheumatoid arthritis with unaffected carpal bones 2009, Licensed under a Creative Commons licence. Available for free at:  https://commons.wikimedia.org/wiki/File:Rheumatoid_arthritis_with_unaffected_carpal_bones_2009.jpg (Accessed: 17 January 2024).

Right: Image source: Wikimedia Commons (2017). Rheumatoid arthritis with carpal ankylosis 2017, Licensed under a Creative Commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Rheumatoid_arthritis_with_carpal_ankylosis_2017.jpg (Accessed: 17 January 2024).

Alongside clinical judgement, the ACR/EULAR (American College of Rheumatology/European League Against Rheumatism) Classification Criteria (2010) can be used to identify those with early RA who are likely to develop chronic RA. It cannot be used to exclude RA, and indeed, over time, the score may change as the condition evolves. In those who have clinical synovitis in one joint or more, which is not better explained by another pathology, a score of six or more is suggestive of definite RA (points scored for joint involvement, serology, acute phase reactants and duration of symptoms).