12.

Chapter 5 Synovial Fluid Analysis

Manual of Rheumatology and Outpatient Orthopedic Disorders


Chapter 5 Synovial Fluid Analysis

Richard Stern

Synovial fluid studies
Diagnosis by fluid group

Synovial fluid analysis is an extremely useful diagnostic tool in the evaluation of rheumatic diseases. It should be included in the initial evaluation of most arthritic conditions. It can yield a specific diagnosis in infectious and crystal-induced arthritis and can be helpful in the diagnosis of other arthritic diseases.

I. Synovial fluid studies

  1. Gross examination alone can be quite helpful in establishing the nature of a joint fluid. After air bubbles are allowed to clear, a heparinized specimen is examined for the following:
    1. Color . Normal synovial fluid is straw-colored. Inflammatory fluids range from yellow to greenish yellow. Hemarthrosis occurs in patients with coagulation disorders, trauma, neoplasms, and tuberculous arthritis and in patients receiving anticoagulant therapy .
    2. Clarity. Normal synovial fluids are clear enough that print can be read through them. As inflammation increases from mild to marked , the fluid becomes first translucent and then opalescent.
    3. Viscosity . Synovial fluid viscosity is tested by allowing a drop of fluid to fall from the needle tip. Normal synovial fluids are quite viscous, and a string of fluid will form. Because viscosity is decreased in inflammatory synovial fluids, no string sign is seen.
    4. Mucin clot. If 1 mL of synovial fluid is added to 3 mL of 2% acetic acid, a firm mucin clot will form. When acetic acid is added to an inflammatory fluid, a poor clot results. This test is rarely used today.
  2. Cell count. This is performed on a counting chamber. However, because often only few cells are present, the initial count can be taken with the specimen undiluted. If there are too many cells to count, appropriate dilution can be achieved with normal saline solution. (Diluents for white blood cells precipitate mucin.) Often, both red and white blood cells can be counted on the same chamber . Remember the ratio of RBCs/WBCs is ~750/1. This can be important in hemorrhagic fluids that are inflammatory or infected.
  3. Polarizing microscopy of a specimen of heparinized fluid is used to perform a crystal examination (see Chapter 37). A useful mnemonic for differentiating urate crystals from calcium pyrophosphate is U-Pay-Peb; urate crystals parallel to the polarizer axis appear yellow, and urate crystals perpendicular to the polarizer axis appear blue. The opposite is true for the calcium pyrophosphate crystals of pseudogout. Urate crystals are needle-shaped and calcium pyrophosphate crystals are rhomboid. Remember that the finding of crystals does not rule out the possibility of an infection.
  4. Microbiologic studies
    1. Stains should include both Gram and acid-fast methods .
    2. Cultures should include routine bacterial studies. Fungal and mycobacterial cultures are ordered as clinically necessary. Synovial fluids and extraarticular sites suspected of harboring gonococci should also be plated on Thayer-Martin material at the bedside, as gonococci are fastidious and difficult to grow.
  5. Biochemical studies
    1. Glucose . Determination of synovial fluid glucose, when interpreted with a simultaneous serum value, is helpful in diagnosing infectious arthritis. In bacterial infection or tuberculosis, the synovial fluid glucose will be less than half the serum value. Occasionally, low values may be seen in rheumatoid arthritis (RA).
    2. Protein determination does not provide additional useful information and should not be routinely ordered.
    3. Complement may be decreased in RA, but the test is rarely helpful for diagnosis because synovial fluid complement is usually normal in early RA.

II. Diagnosis by fluid group (Table 5-1). Synovial fluid can be divided into three groups based on the degree of inflammation.


Table 5-1. Synovial fluid analysis



  1. Group 1 fluids are clear and transparent and have few white cells on cell count. They include normal, osteoarthritic, and systemic lupus erythematosus (SLE) joint fluids.
  2. Group 2 fluids generally have a higher white cell count and are not as clear as group 1 fluids; they appear translucent. This group includes fluids from most noninfectious, inflammatory arthritic conditions such as gout, pseudogout, psoriatic arthritis, Reiter's syndrome, and RA. Leukemia or lymphoma occasionally presents in this category, but the differential count reveals more than 90% mononuclear cells.
  3. Group 3 fluids are opalescent or purulent. Group 3 fluids include those from bacterial infections and tuberculosis (although joint fluid from gonococcal arthritis can be either group 2 or group 3). Group 3 fluids typically have 50,000 to 300,000 white blood cells per milliliter; these are mostly neutrophils. Occasionally, the synovial fluid from a patient with an inflammatory arthritic condition such as RA may have as many as 50,000 to 75,000 white cells per milliliter and appears opalescent or even purulent. As Table 5-1 shows, there is considerable overlap between the various arthritic diseases; this table is meant to serve as a guideline rather than provide a rigid set of criteria.

Books@Ovid
Copyright 2000 by Lippincott Williams & Wilkins
Stephen A. Paget, M.D., Allan Gibofsky, M.D., J.D. and John F. Beary, III, M.D.
Manual of Rheumatology and Outpatient Orthopedic Disorders

-->


Manual of Rheumatology and Outpatient Orthopedic Disorders (LB Spiral Manuals)
Manual of Rheumatology and Outpatient Orthopedic Disorders (LB Spiral Manuals)
ISBN: N/A
EAN: N/A
Year: 2000
Pages: 315

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net