Health Questions and Answers

Question: What are the “string” and “mucin clot” tests?


The primary component of joint fluid is hyaluronic acid. It is quite viscous and makes a “string” when expressed from a syringe as a single drop. Dilute acetic acid causes hyaluronate and protein to clump and fall to the bottom of a test tube (producing the famous “mucin clot”). Inflammatory mediators cause fragmentation of the hyaluronate-protein complex, rendering it unable to form a good mucin clot.

Reference:  Hochberg MC (ed). Rheumatology, 3rd ed. St. Louis, Mosby, 2003

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