Shoulder Arthrocentesis Laboratory Medicine

Updated: Feb 13, 2023
  • Author: Stephen Kishner, MD, MHA; Chief Editor: Erik D Schraga, MD  more...
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Laboratory Medicine

Laboratory Medicine Summary

Synovial Fluid Analysis

The following may be included in analysis:

  • Gram stain and culture should be performed on all samples suspicious for infection.
  • Total Leukocyte count and differential support differentiation between noninflammatory and inflammatory joint conditions.
    • If macrophage predominance (>80%): consider "Milwaukee shoulder"
  • Polarized microscopy evaluates for the presence of pathological crystals.
  • If inflammation or infection is not present, normal synovial fluid glucose is within 20 mg% of serum value.
  • Inflammation increases normal synovial fluid protein, and the average is approximately 2 mg% (33% of the serum total protein).
  • 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:

  • Appearance of artifactual crystals
  • Decrease in leukocyte count (from cell disruption)
  • Decrease in number of crystals (especially calcium pyrophosphate dihydrate) [5]

Please refer to Joint Fluid Interpretation / Overview/Joint Fluid Interpretation for additional information.