Joint fluid aspiration analysis
| Gout / Pseudo-gout | Septic arthritis | |
|---|---|---|
| Colour | Yellow | Yellow |
| Clarity | Cloudy | Cloudy / opaque |
| Viscosity | Decreased | Decreased |
| WBC | 2000 – 50,000 cells/mm3 | > 20,000 cells/mm3 |
| Neutrophils | ≥ 50 % | ≥ 75 % |
| Gram stain | Negative | Positive but may be negative |
| Crystals | Gout – needle negative birefringent crystals Pseudogout: rhomboid positively birefringent crystals | Negative |
Typical joint fluid analysis findings in non-inflammatory joint effusions (e.g., trauma, osteoarthritis) include:
- WBC: 200 – 2000 cells/mm3
- Neutrophils: < 25 %
- Gram stain: negative
- Crystals: negative