Glossary
A-Z reference of hirudotherapy, leech biology, and clinical terms
Last Updated: March 5, 2026Reviewed by: Andrei Dokukin, MD
Last updated: March 14, 2026
This glossary provides definitions for key terms used throughout the ASH website, covering hirudotherapy, leech biology, hemostasis, pharmacology, and clinical practice.
A
- Aeromonas hydrophila
- Gram-negative rod bacterium; obligate symbiont in the leech gut. Primary infectious risk of medicinal leech therapy, accounting for 88% of post-treatment infections.
- Antistasin
- A 119-amino-acid Factor Xa inhibitor (Kunitz-type serine protease inhibitor) from leech SGSry glands. Conceptual precursor to modern FXa-inhibitor drugs.
- Apyrase
- Enzyme that hydrolyzes ADP, inhibiting ADP-dependent platelet activation. Part of the leech multi-target anti-hemostatic strategy.
- aPTT (Activated Partial Thromboplastin Time)
- Laboratory test measuring intrinsic pathway coagulation. Prolonged by hirudin and other leech-derived anticoagulants.
B
- Bdellins
- Family of serine protease inhibitors from leech SGS. Inhibit trypsin and plasmin. Named from Greek bdella (leech).
- Bivalirudin
- Synthetic 20-amino-acid peptide DTI (direct thrombin inhibitor), FDA-approved 2000. Derived from leech hirudin structure-activity studies. Class I recommendation for STEMI PCI.
- Bloodletting (therapeutic)
- Historical practice of blood removal for therapeutic purposes. Modern hirudotherapy produces controlled local bloodletting of 35-50 mL per leech.
C
- Calin
- Leech salivary protein that inhibits platelet adhesion to collagen by 85-87%. Responsible for prolonged post-bite bleeding (4 to 24 hours). No pharmaceutical analog exists.
- CBER (Center for Biologics Evaluation and Research)
- FDA center that assumed regulatory jurisdiction over medicinal leeches on December 30, 2024, transferred from CDRH.
- CDRH (Center for Devices and Radiological Health)
- Former FDA center responsible for medicinal leech regulation (until December 2024). Oversaw 510(k) clearance of medicinal leeches as medical devices.
- Complement system
- Part of innate immunity; cascade of proteins (C1-C9) that lyse pathogens. Leech saliva contains complement inhibitors (C1, C3 modulators).
- CPT code 17999
- Unlisted procedure code most commonly used for billing medicinal leech therapy. No dedicated CPT code exists.
D
- Dabigatran
- First oral direct thrombin inhibitor (FDA 2010). Conceptual lineage from hirudin crystallography and structure-activity studies. RE-LY trial: superior to warfarin for AF.
- Decorsin
- RGD-containing GP IIb/IIIa antagonist from the North American leech Macrobdella decora. Related to eptifibatide/tirofiban class.
- Desirudin
- Recombinant hirudin variant 2 (HV2). FDA-approved 2003 for DVT prophylaxis in hip replacement surgery.
- Destabilase
- Unique bifunctional enzyme with isopeptidase and lysozyme activity. Can dissolve aged fibrin clots resistant to all known thrombolytics. Crystal structure at 1.1 angstrom (2023).
- DNIC (Diffuse Noxious Inhibitory Controls)
- Pain modulation mechanism where one painful stimulus inhibits another. Leech bite may activate DNIC via conditioned pain modulation.
- DTI (Direct Thrombin Inhibitor)
- Drug class that directly inhibits thrombin (Factor IIa). All approved DTIs trace their lineage to leech hirudin.
E
- Eglin c
- Small (70 AA) serine protease inhibitor from leech SGS. Potent inhibitor of neutrophil elastase and cathepsin G. Potential for ARDS/COPD therapy.
- Evidence Grade (GRADE)
- Framework for rating evidence quality: High (consistent RCT results), Moderate (RCTs with limitations), Low (observational), Very Low (case reports/expert opinion).
F
- 510(k)
- FDA premarket notification pathway. Medicinal leeches cleared under K040187 (2004), K132958 (2014), K140907 (2015) as FDA-cleared medical devices.
- Factor Xa
- Serine protease in the coagulation cascade. Target of leech antistasin and pharmaceutical drugs rivaroxaban, apixaban, edoxaban.
- Fibrin
- Insoluble protein formed from fibrinogen during coagulation. Forms the mesh structure of blood clots. Cross-linked fibrin is the target of destabilase.
G
- GP IIb/IIIa
- Platelet integrin receptor for fibrinogen binding and aggregation. Target of leech decorsin/ornatin and drugs eptifibatide/tirofiban.
- GRADE framework
- Grading of Recommendations Assessment, Development and Evaluation. Standard methodology for rating clinical evidence quality used throughout this site.
H
- Hematophagy
- Blood-feeding behavior. Medicinal leeches are obligate hematophages, feeding once every 3-6 months in the wild.
- Hirudo medicinalis
- European medicinal leech species. One of three Hirudo species used clinically (with H. verbana and H. orientalis).
- Hirudo verbana
- The species most commonly sold as H. medicinalis. Primary species in commercial leech supply for medical use.
- Hirudin
- The most potent natural thrombin inhibitor known (Kd ~20 femtomolar). 65-amino-acid polypeptide from leech SGSry glands. Parent molecule of all DTI drugs.
- Hirudotherapy
- The clinical application of medicinal leeches (Hirudo spp.) for therapeutic purposes. FDA 510(k)-cleared for venous congestion in microsurgical salvage.
- Hyaluronidase
- Enzyme that degrades hyaluronic acid in the extracellular matrix. Acts as a spreading factor for other salivary components.
I
- Isopeptidase
- Enzyme that cleaves isopeptide bonds. Destabilase is the only known enzyme with this activity, enabling dissolution of stabilized fibrin.
K
- K040187
- First FDA 510(k) clearance for medicinal leeches (Ricarimpex SAS, June 2004). Established the indications language used by all subsequent clearances.
- Kininogenase
- Leech salivary enzyme that cleaves kininogens to release bradykinin, producing vasodilation and increased vascular permeability.
L
- LCI (Leech Carboxypeptidase Inhibitor)
- Inhibitor of carboxypeptidase A and B from leech SGS. Prevents inactivation of bradykinin and other vasoactive peptides.
- LDTI (Leech-Derived Tryptase Inhibitor)
- Potent and specific inhibitor of mast cell tryptase. May contribute to anti-inflammatory effects by preventing mast cell-mediated inflammation.
- Lepirudin
- Recombinant hirudin variant 1 (HV1). FDA-approved 1998 for HIT-associated thrombosis. Withdrawn 2012 due to anti-hirudin antibody formation.
M
- Microsurgery
- Surgical specialty using microscope-assisted techniques. Venous congestion in microsurgical flaps is the primary FDA-cleared indication for medicinal leeches.
N
- NRN (Product Code)
- FDA product code for medicinal leeches under the medical device classification system.
- Neovascularization
- Growth of new blood vessels. In microsurgery, leeches provide temporary venous decompression while neovascularization develops over 3-7 days.
O
- Off-label use
- Use of an FDA-cleared device for indications other than those specified in the clearance. Legal when clinically justified but requires informed consent disclosure.
- Ornatin
- RGD-containing GP IIb/IIIa antagonist from the leech Placobdella ornata. Closely related to decorsin.
P
- Piyavit
- Pharmaceutical formulation derived from whole leech extract. Used in Russian clinical practice. Not FDA-cleared or approved in the United States.
R
- RGD (Arg-Gly-Asp)
- Tripeptide motif recognized by integrin receptors. Found in leech decorsin/ornatin; basis for eptifibatide and tirofiban design.
S
- Saratin
- Leech salivary protein that blocks von Willebrand factor binding to collagen, reducing platelet adhesion by >80%. No approved pharmaceutical analog.
- SGS (Salivary Gland Secretion)
- The complete secretome of the medicinal leech SGSry glands. Contains 434+ identified proteins across multiple functional groups.
- Somatoautonomic reflex
- Neurological pathway by which cutaneous (somatic) stimulation modulates autonomic and visceral organ function via spinal reflex arcs. Proposed mechanism underlying some site-specific hirudotherapy effects.
T
- Thrombin (Factor IIa)
- Central serine protease of the coagulation cascade. Converts fibrinogen to fibrin, activates platelets, and activates Factors V, VIII, XI, XIII. Primary target of hirudin.
- Tier A/B/C
- ASH regulatory classification: Tier A = FDA-cleared, Tier B = clinical evidence (not FDA-cleared), Tier C = investigational/research priority.
- TMP-SMX
- Trimethoprim-sulfamethoxazole (Bactrim). Component of dual antibiotic prophylaxis for Aeromonas prevention in leech therapy.
V
- Venous congestion
- Accumulation of blood due to inadequate venous drainage. The specific pathology addressed by FDA-cleared medicinal leech therapy in microsurgery.
- von Willebrand factor (vWF)
- Glycoprotein mediating platelet adhesion to collagen. Target of leech calin and saratin.
Z
- Head zones
- Dermatomes where visceral organ pathology manifests as referred cutaneous pain/hyperesthesia. Used to guide application point selection in hirudotherapy.