Synovial fluid analysis
- Dalton E Sholter, MD, FRCPC
Dalton E Sholter, MD, FRCPC
- Associate Clinical Professor of Medicine
- University of Alberta
- Anthony S Russell, MD, FRCPC
Anthony S Russell, MD, FRCPC
- Professor of Medicine
- University of Alberta
- Section Editors
- Robert H Shmerling, MD
Robert H Shmerling, MD
- Section Editor — Diagnostic Issues in Rheumatology
- Associate Professor of Medicine
- Harvard Medical School
- Stephen B Calderwood, MD
Stephen B Calderwood, MD
- Editor-in-Chief — Infectious Diseases
- Section Editor — Bacterial Infections
- Professor of Medicine (Microbiology and Immunobiology)
- Harvard Medical School
Synovial fluid analysis is helpful for determining the underlying cause of arthritis, particularly for septic or crystal-induced arthritis. The white cell count, differential count, cultures, Gram stain, and crystal search using polarized light microscopy are the most useful studies. An overview of synovial fluid analysis in the native joint is discussed here. Septic arthritis, prosthetic joint infections, gonococcal arthritis, and fungal and mycobacterial arthritis are discussed in detail separately. (See "Septic arthritis in adults" and "Prosthetic joint infection: Epidemiology, clinical manifestations, and diagnosis" and "Prosthetic joint infection: Treatment" and "Disseminated gonococcal infection" and "Skeletal tuberculosis".)
Arthrocentesis with synovial fluid analysis should be attempted in all patients who have a joint effusion or signs suggestive of inflammation within the joint, without a known cause. The most important reason to perform a synovial fluid analysis is to evaluate for septic arthritis in a patient presenting with an acutely swollen joint that is painful and warm. (See "Septic arthritis in adults".)
Synovial fluid analysis is also particularly important for definitively diagnosing gout or pseudogout. In combination with a negative Gram stain and bacterial cultures, a diagnosis of gout or pseudogout may be established by confirming the presence of crystals of monosodium urate (MSU) or calcium pyrophosphate dihydrate (CPPD) in a patient presenting with unexplained inflammatory arthritis. (See "Clinical manifestations and diagnosis of gout" and "Clinical manifestations and diagnosis of calcium pyrophosphate crystal deposition (CPPD) disease".)
Synovial fluid analysis is also helpful in narrowing the differential diagnosis by distinguishing between categories of joint effusions (ie, inflammatory versus noninflammatory) (table 1), and to diagnose hemarthrosis (algorithm 1). (See 'Categories of joint effusions' below.)
CATEGORIES OF JOINT EFFUSIONS
Results of synovial fluid analysis can be used to categorize the fluid as noninflammatory, inflammatory, septic, or hemorrhagic based upon the clinical and laboratory analysis (table 2).
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- CATEGORIES OF JOINT EFFUSIONS
- SPECIMEN COLLECTION AND HANDLING
- Microscopic examination
- ROUTINE COMPONENTS OF SYNOVIAL FLUID ANALYSIS
- Gross appearance
- Crystal analysis
- - Monosodium urate crystals
- - Calcium pyrophosphate dihydrate crystals
- - Other crystals
- Nucleated (white) cell count and differential
- Gram stain
- Bacterial culture
- SUMMARY AND RECOMMENDATIONS