AUBF Synovial

• Synovial fluid, also known as joint fluid, contains high levels of Hyaluronic acid, which is derived from the Latin term for egg, ovum.
• Normal viscous synovial fluid resembles an egg white.
• Synovial fluid is the fluid circulating in the moveable joints (diarthroses) of the body.
• Synovial fluid is formed as an ultrafiltrate of plasma across the synovial membrane.
• The functions of synovial fluid include reducing friction between bones during movement, providing lubrication in the joints, providing nutrients to the articular cartilage, and lessening joint compression during walking and jogging.
• The method of collection for synovial fluid is arthrocentesis, which involves a syringe moistened with heparin.
• The three tubes used for synovial fluid collection are: Tube 1 for heparinized tube or SPS for Microbiology (gram stain & culture), Tube 2 for heparin or Liquid EDTA for Hematology (cell count), and Tube 3 for plain tube for chemistry and other significant tests (sodium fluoride tube for glucose analysis).
• Do not use powered anticoagulant in synovial fluid collection as it interferes in crystal identification.
• Microbiological tests for joint infections include Gram stain and culture, and organisms implicated in joint infections include S. aureus, Streptococcus, Haemophilus spp., N. gonorrheae, and B. burgdorferi.
• Testing on synovial fluid is done on a STAT basis to avoid cell lysis and possible changes in the crystals.
• Uric acid levels in synovial fluid are equal to blood uric acid levels.
• Uric acid levels are increased in cases of GOUT.
• Serological tests for joint infections are usually done in patients with Rheumatoid Arthritis and Systemic Lupus Erythematosus because they cause severe inflammation of the joints.
• Identification of antibodies against B. burgdorferi is done in cases where arthritis is present as a complication of Lyme disease.
• Streptococcus, Haemophilus spp., and N. gonorrheae are also implicated in joint infections.
• B. burgdorferi is a common organism in cases of Lyme disease, and serologic tests are preferred for its detection.
• S. aureus is the most common cause of adult joint infections.
• S. aureus is responsible for most adult joint infections.
• Normal value for synovial fluid volume is less than 3.5 mL, indicating inflammation or infection.
• Synovial fluid with a milky appearance indicates the presence of crystals.
• Normal color for synovial fluid is colorless to pale yellow.
• Normal clarity for synovial fluid is clear.
• Viscosity of synovial fluid must form a 4-6cm long string (String Test).
• Lactate differentiates inflammatory from septic arthritis, with a normal value < 250 mg/dl and lactate values > 250 mg/dl seen in cases of septic and rheumatoid arthritis.
• Glucose is the most frequently done chemical test in synovial fluid, with a normal value < 10mg/dl lower than blood glucose and markedly decreased associated with inflammatory (Group II) or septic (Group III) disorders.
• Total protein in synovial fluid is approximately 1/3 of serum TP, with a normal value < 3 g/dl and increased TP associated with inflammatory and hemorrhagic disorders.
• Routine synovial fluid differential count includes white blood cells (WBC), monocytes and macrophages, neutrophils, lymphocytes, and red blood cells (RBCs).
• Other tests for synovial fluid include Hyaluronate Polymerization Test (Rope’s Test/Mucin Clot Test), reagent: 2-5% acetic acid, grading: Good – Solid clot, Fair – Soft clot, Poor – Friable clot, Very poor – No clot.
• Very viscous fluid must first be pre-treated by adding one drop of 0.05% hyaluronidase in phosphate buffer/mL of fluid and incubating at 37 ° C for 5 minutes.
• No dilution is necessary for clear fluids, but dilute if cloudy or milky.
• Other crystals in synovial fluid include hydroxyapatite crystals (Calcium Phosphate) resulting from calcified cartilage degeneration, cholesterol crystals, corticosteroids from injections, and calcium oxalate crystals (envelope) from renal dialysis patients.
• Synovial fluid crystals are normally absent, but can be identified as needles in cases of gout and as rods or rhombic shaped crystals in cases of pseudogout.
• Septic inflammation is characterized by increased neutrophils, while non-septic inflammation is characterized by increased lymphocytes.
• Total WBC count is the most frequently performed test on synovial fluid.
• Synovial fluid contains hyaluronic acid which acts as a shock absorber