From the Guidelines
The initial laboratory tests for suspected reactive arthritis (ReA) should include C reactive protein (CRP)/erythrocyte sedimentation rate (ESR), full blood cell count, transaminase levels, renal function, and urine analysis. This recommendation is based on the most recent and highest quality study available, which emphasizes the importance of a careful history taking and clinical examination to guide laboratory testing and additional procedures 1.
Key Laboratory Tests
- C reactive protein (CRP)/erythrocyte sedimentation rate (ESR) to assess inflammation
- Full blood cell count to evaluate for any abnormalities in blood cell counts
- Transaminase levels to assess liver function
- Renal function tests to evaluate kidney function
- Urine analysis to assess for any urinary tract abnormalities
While other studies may suggest additional tests such as HLA-B27 testing, autoimmune blood panels, and imaging studies, these are not recommended as part of the initial laboratory workup for suspected reactive arthritis 1. The initial focus should be on identifying inflammatory markers, assessing organ function, and detecting any potential triggering infections.
Additional Considerations
- Joint fluid analysis may be performed if effusion is present to examine for cell count, crystal analysis, and culture
- Serological tests for sexually transmitted infections may be essential in certain cases, but are not part of the initial laboratory workup
- Imaging studies may be ordered subsequently to evaluate joint damage or exclude other conditions, but are not part of the initial laboratory tests.
From the Research
Initial Laboratory Tests for Suspected Reactive Arthritis (ReA)
The initial laboratory tests for suspected reactive arthritis (ReA) are not explicitly stated in the provided studies. However, based on the information available, the following tests may be relevant:
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level, which are commonly used to assess inflammation 2, 3, 4, 5
- Complete blood count (CBC) with differential, which can help identify any underlying infections or inflammatory processes 5
- Rheumatoid factor and anti-citrullinated protein antibody tests, which can help differentiate ReA from other forms of arthritis, such as rheumatoid arthritis 3, 5
- Synovial fluid analysis, which can help diagnose periprosthetic joint infection in patients with inflammatory arthritis 2
Limitations of Laboratory Tests
It is essential to note that laboratory tests have limitations in diagnosing and managing ReA and other rheumatic diseases. For example:
- More than 30% of patients with rheumatoid arthritis have negative tests for rheumatoid factor or anti-CCP antibodies, and 40% have a normal ESR or CRP 3
- The presence of a rheumatoid factor or anti-citrullinated protein antibody, or elevated CRP level or ESR, suggests a diagnosis of rheumatoid arthritis, but these tests are not specific for ReA 5
Key Points
- The diagnosis of ReA is mainly clinical, based on acute oligoarticular arthritis of larger joints developing within 2-4 weeks of the preceding infection 6
- Laboratory tests, such as ESR, CRP, and CBC, can help assess inflammation and identify underlying infections or inflammatory processes 2, 3, 4, 5
- The limitations of laboratory tests should be considered when diagnosing and managing ReA and other rheumatic diseases 3