Joint Fluid Analysis
Synovial fluid analysis utilized to help diagnose the cause of joint inflammation, pain, swelling, and fluid accumulation.
Diseases and conditions affecting one or more joints and the synovial fluid include: Infectious diseases that may originate in the joint or spread there from other places in the body, bleeding disorders and/or joint injury can lead to blood in the synovial fluid, inflammatory diseases causing crystal formation and accumulation, synovitis, or other immune responses, and degenerative diseases.
Synovial fluid analysis ordered when there is a condition or disease involving one or more of their joints, and when the following signs and symptoms are present: Joint pain, redness over the joint, joint inflammation and swelling, synovial fluid accumulation and sometimes to monitor a known joint condition.
Normal synovial fluid usually contains a small amount of glucose and protein and may have a few white blood cells (WBCs) and red blood cells (RBCs).
Based primarily on the number of cells in the aspirated , joint effusions are classified as non–inflammatory, inflammatory, or highly inflammatory.
Non- inflammatory joint effusions are relatively acellular, usually containing less than 1000 cells per millimeter3 whereas inflammatory effusions such as those seen in rheumatoid arthritis or psoriatic arthritis usually contain 5 to 20,000 cells/millimeter3.
Septic arthritis should be suspected if the synovial fluid cell count is greater than 50,000 cells per milliliter3 and mainly polymorphonuclear leukocytes.
Bloody joint effusions are primarily related to joint trauma or bleeding disorders.
Joint abnormalities including osteoarthritis, rheumatoid arthritis, gout, and infection can cause inflammation, swelling, an accumulation of synovial fluid, and sometimes bleeding into one or more joints.
Synovial fluid’s normal appearance is usually straw colored and clear.
Synovial fluid is moderately viscous and of it from a syringe needle will form a stringlike sibstance a few inches long.
Less viscous fluid may be seen with inflammation, and cloudy appearing synovial fluid may indicate the presence of microorganisms, white blood cells, or crystals.
Reddish synovial fluid suggests the presence of blood, as does cloudy fluid.
Synovial fluid analysis include: glucose, protein, LDH, and uric acid.
Synovial fluid glucose is usually mildly lower than blood glucose levels, but may be significantly lower with joint inflammation and infection.
Synovial fluid protein levels are increased with bacterial infection of the joint.
Lactate dehydrogenase levels may be increased in rheumatoid arthritis, infectious arthritis, or gout.
Synovial fluid uric acid levels increased with gout.
On microscopic examination normal synovial fluid has few white blood cells and red blood cells but no microorganisms or crystals present.
Increased WBCs may be seen with infections and with gout and rheumatoid arthritis.
An increased number of neutrophils in synovial fluid may be seen with bacterial infections.
Synovial fluid with more than 2% eosinophils may suggest Lyme disease.
Synovial fluid is examined under polarized light to identify the presence of crystals.
Needle-like monosodium urate crystals are associated with gout.
Calcium pyrophosphate crystals are associated with pseudogout.
If Infectious disease is suspected Gram stain allows for the direct observation of bacteria or fungi under a microscope.
No microorganisms should be present in synovial fluid, but if there are no microorganisms present, it does not rule out an infection as they may be present in small numbers or their growth may be inhibited because of prior antibiotic therapy.
Less commonly ordered tests include AFB smear and culture, but molecular tests methods for Mycobacteria tuberculosis are more sensitive and specific than traditional cultures.
A blood or urine uric acid or blood glucose should be analyzed to compare concentrations with those in the synovial fluid.