Heparin

Heparin is a glycosaminoglycan (a long, negatively charged sugar chain) stored in mast cell granules. Inside the granule, it serves as a structural scaffold — Histamine, Tryptase, and other mediators are ionically bound to the heparin matrix. During Degranulation, heparin is released along with everything bound to it.

What It Does Once Released

Heparin’s primary known function is anticoagulation — it inhibits blood clotting by activating antithrombin III, which in turn inhibits thrombin and factor Xa in the coagulation cascade.

In the context of MCAS, heparin release can contribute to:

• Easy bruising
• Heavy menstrual bleeding
• Prolonged bleeding from minor cuts
• Potentially, over long periods, bone density loss (heparin promotes osteoclast activity)

As a Diagnostic Marker

Heparin is one of the mediator markers that can be measured in blood during suspected mast cell activation episodes. It’s included in some MCAS diagnostic workups but is not routinely tested in most clinical settings.