Studies for synovial fluid analysis
What studies should be performed for synovial fluid analysis?
Visual inspection commenting on synovial fluid clarity and color should be performed. Because the single most important determination of synovial fluid analysis is for the presence of infection, Gram stain and culture should be performed on samples from joints with even relatively low suspicion for infection. Determining total leukocyte count and differential helps in differentiating between noninflammatory and inflammatory joint conditions. Lastly, polarized microscopy should be performed to evaluate for the presence of pathological crystals. Chemistry determinations, such as glucose and total protein, are unlikely to yield helpful information beyond that obtained by the previous studies; therefore, they should not be routinely ordered. Normal synovial fluid glucose is within 20 mg/dL of the serum value unless inflammation or infection is present. Normal synovial fluid protein averages around 2 g/dL (33% of the serum total protein) and increases with inflammation. Lactate dehydrogenase, uric acid, pH, electrolytes, and immunological studies are of no value and should not be ordered. New techniques to detect indolent infections including PCR using organism-specific primers or amplifying bacterial 16S ribosomal sequences may be useful but are less sensitive on synovial fluid than synovial tissue. Synovial fluid alpha-defensin levels are elevated in >95% of periprosthetic joint infections