This is indicated and indeed obligatory in any patient with a monarthritis where crystal synovitis (gout or pseudogout) or septic arthritis is considered part of the differential diagnosis. It is one of the few tests where failure to undertake the synovial fluid analysis is likely to significantly influence making a correct diagnosis and, consequently, initiating appropriate therapy. Thus, synovial fluid culture and polarized light microscopy are essential. Reliance on synovial white count alone is often misleading.

Learning Points

• Rheumatologic diagnoses are principally clinical in nature.
• There are few diagnostic tests and the use of screening panels is unhelpful and often misleading.
• Most serologic tests lack specificity and sensitivity.
• Hyperuricemia and gout, although associated, are not synonymous.
• Synovial fluid analysis is useful, particularly in acute monarthritis.

Suggested Reading

Shojania K. Rheumatology: 2. What laboratory tests are needed? CMAJ 2000;162:1157-63.

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