SYNOVIAL FLUID MUCIN-CLOT ("Ropes test")
This measures how well-polymerized the hyaluronic acid is.
A few drops of synovial fluid are added to 10 mL or so of 5% acetic acid in a beaker and swirled for a minute. The resulting "clot" is rated:
- good: a solid clot in a clear solution
- fair: a soft clot in a slightly turbid solution
- poor: a friable (crumbly) clot in a turbid solution
- very poor: no clot
Inflammation in the joint space damages the hyaluronic polymers, shortening them.
Thus, the "mucin clot" is:
- GOOD in osteoarthritis, trauma, and hemophilic arthritis
- FAIR in subacute and chronic inflammatory diseases such as lupus or rheumatoid arthritis
- POOR TO VERY POOR in septic and acute crystalline arthritis.
SYNOVIAL FLUID STRING TEST ("Viscosity test")
This test (not to be confused with Ropes, which is a name) measures the polymerization of hyaluronic acid plus how much it has been diluted by the rapid entry of extracellular fluid into an inflamed joint.
All the different ways of doing this test involve stringing a drop of the fluid out (from the end of a syringe, etc., but not between your fingers because of the HIV risk). If you can pull the drop into a string longer than 3 cm, the test is normal.
Interpretation is the same as for the mucin clot test.