From the Guidelines
For a gout flare, the most important laboratory test is joint fluid analysis, which is the gold standard for diagnosis, as it allows for the identification of monosodium urate crystals under polarized microscopy 1. This test is crucial for confirming the diagnosis of gout and ruling out other conditions like septic arthritis or pseudogout.
- Other laboratory tests that may be recommended during a gout flare include:
- Serum uric acid level
- Complete blood count (CBC)
- Comprehensive metabolic panel (CMP)
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP)
- Renal function tests (BUN, creatinine)
- Liver function tests
- According to the 2018 updated European League Against Rheumatism evidence-based recommendations for the diagnosis of gout, synovial fluid analysis is recommended in every person with suspected gout, as it allows for a definitive diagnosis of gout 1.
- The American College of Physicians also recommends the use of synovial fluid analysis for the diagnosis of acute gout, although the evidence is considered low-quality 1.
- It is essential to note that during an acute flare, uric acid levels may be normal or low, so treatment decisions should not be based solely on uric acid levels during the acute phase 1.
- After the flare resolves, follow-up uric acid testing is recommended to guide long-term management, with a target level below 6 mg/dL to prevent future attacks 1.
From the Research
Laboratory Tests for Gout Diagnosis
The following laboratory tests are recommended during a gout flare:
- Arthrocentesis to analyze synovial fluid for monosodium urate crystals 2, 3, 4
- Synovial fluid or tophus analysis to confirm the diagnosis of gout 2, 3, 4
- Gram staining and bacterial culture to rule out septic arthritis 4
- Soft tissue ultrasonography to detect affected synovial tissue and monosodium urate crystals within the synovial fluid 4, 5, 6
- Dual energy computed tomography (CT) and magnetic resonance imaging (MRI) for certain indications 4
Blood Tests
- Serum uric acid levels, although these may decrease during acute attacks and do not confirm or exclude gout 2
- Renal function tests, such as creatinine levels, to assess kidney function 2, 4