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Septic arthritis may be caused by any number of different microorganisms and results in erythematous, painful, swollen joints.
Tests generally appear in the order most useful for common clinical situations
| Test name: CBC with Platelet Count & Automated Differential |
| ARUP #: 0040003 |
| Methodology: Automated Cell Count with Flow Cell Differential |
| Use: Initial screening test in septic arthritis |
| Limitations: Normal WBC count does not rule out septic arthritis |
| Test name: Cell Count, Body Fluid |
| ARUP #: 0095019 |
| Methodology: Cell Count/Differential |
| Use: Cornerstone test for differential diagnosis on synovial fluid aspirate |
| Test name: Crystals (Local Clients Only) |
| ARUP #: 0009500 |
| Methodology: Microscopy/Polarizing Microscopy |
| Use: Rule out arthritis due to crystalline deposits |
| Test name: Gram Stain |
| ARUP #: 0060101 |
| Methodology: Stain/Microscopic Exam |
| Use: Identify bacteria in the synovial fluid |
| Limitations: Low sensitivity (30-50%) negative gram stain does not rule out septic arthritis |
| Test name: Sedimentation Rate, Westergren (ESR) |
| ARUP #: 0040325 |
| Methodology: Westergren |
| Use: May be helpful in initial diagnosis of septic arthritis |
| Limitations: Normal ESR does not rule out septic arthritis |
| Test name: C-Reactive Protein |
| ARUP #: 0050180 |
| Methodology: Quantitative Immunoturbidimetric |
| Use: May be helpful in initial diagnosis of septic arthritis |
| Limitations: Normal CRP does not rule out septic arthritis |
| Test name: Blood Culture |
| ARUP #: 0060102 |
| Methodology: Continuous Monitoring Blood Culture/Identification |
| Use: Identify presence of bacteremia |
| Limitations: Positive in 50-70% of patients with septic arthritis Time-sensitive test Testing is limited to the University of Utah Health Sciences Center only |
| Test name: Body Fluid Culture (Includes Gram Stain 0060101) |
| ARUP #: 0060108 |
| Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Anaerobe culture performed on properly collected specimens |
| Use: 80-97% sensitivity for non-gonococcal septic arthritis |
| Test name: Tissue Culture (Includes Gram Stain 0060101) |
| ARUP #: 0060127 |
| Methodology: Standard reference procedures for bacterial stain, aerobic culture, and identification. Anaerobe culture performed on properly collected specimens. |
| Use: Identify bacteria in periprosthetic tissues |
| Test name: Borrelia burgdorferi Antibodies, Total by ELISA with Reflex to IgG & IgM by Western Blot (Early Disease) |
| ARUP #: 0050267 |
| Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Qualitative Western Blot |
| Comments: Consider in patient with negative cultures and who resides in an endemic area |