Nivelnäyte

Nivelnäyte, or synovial fluid sample, is a sample of the fluid found in a joint collected by arthrocentesis for diagnostic evaluation of joint diseases. It is most commonly obtained from the knee but any accessible joint may be punctured.

Procedure and handling: The procedure is performed under aseptic conditions with local anesthesia. A needle is inserted into the joint to withdraw fluid, sometimes with ultrasound or fluoroscopic guidance. The collected fluid is typically divided into tubes for microbiology, chemistry, and cytology. Samples should be processed promptly; if delayed, they are stored at 4°C and handled to preserve cell integrity.

Analyses performed: Macroscopic assessment records color, clarity, and viscosity. Laboratory analyses include cell count with differential, Gram stain and culture for bacteria, and crystal analysis by polarized light microscopy to detect monosodium urate or calcium pyrophosphate dihydrate crystals. Biochemical tests may measure glucose, protein, lactate, and other markers. Cytology can identify malignant cells when indicated.

Clinical interpretation: Normal synovial fluid is clear and pale yellow with low viscosity and a low cell count. Inflammatory effusions show elevated leukocytes and protein. Septic arthritis typically presents with high neutrophils and often reduced glucose; crystal arthritis reveals characteristic crystals. Culture results guide antimicrobial therapy, while crystal analysis helps distinguish gout or pseudogout from infection or other inflammatory conditions.

Safety and limitations: Arthrocentesis is generally safe but carries risks such as bleeding, infection, or joint injury. Results may be nondiagnostic in some cases, and interpretation should consider the clinical context and imaging findings.