Laboratory Medicine
Laboratory Medicine Summary
Synovial Fluid Analysis
The following may be included in analysis:
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Gram stain and culture should be performed on all samples suspicious for infection.
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Total Leukocyte count and differential support differentiation between noninflammatory and inflammatory joint conditions.
- If macrophage predominance (>80%): consider "Milwaukee shoulder"
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Polarized microscopy evaluates for the presence of pathological crystals.
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If inflammation or infection is not present, normal synovial fluid glucose is within 20 mg% of serum value.
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Inflammation increases normal synovial fluid protein, and the average is approximately 2 mg% (33% of the serum total protein).
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Ordering the following tests is not recommended due to low clinical significance: lactate dehydrogenase, uric acid, pH, electrolytes, and immunological studies.
Synovial fluid should be analyzed immediately after arthrocentesis. Delayed analysis may cause:
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Appearance of artifactual crystals
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Decrease in leukocyte count (from cell disruption)
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Decrease in number of crystals (especially calcium pyrophosphate dihydrate) [5]
Please refer to Joint Fluid Interpretation / Overview/Joint Fluid Interpretation for additional information.
Media Gallery
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Circle represents coracoid process.
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Shoulder arthrocentesis. Insert needle medial to head of humerus and just below tip of coracoid process.
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Shoulder arthrocentesis. Direct needle slightly laterally and superiorly.
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