Glossary
A-Z reference of hirudotherapy, leech biology, and clinical terms
Last Updated: May 27, 2026Reviewed by: Andrei Dokukin, MD
Medical terminology glossaryReference dictionary
Last updated: November 1, 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, with Aeromonas species together accounting for about 88% of leech-associated infections.
- Antistasin
- A 119-amino-acid Factor Xa inhibitor (Kunitz-type serine protease inhibitor) from leech salivary 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 binds collagen and inhibits collagen-mediated platelet adhesion and aggregation. Proposed as one of the factors contributing to the prolonged bleeding after a leech bite. 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). Designed from the X-ray structure of thrombin bound to the synthetic inhibitor NAPAP, not from hirudin. 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 (Val1-Val2 desulfatohirudin, i.e. the natural HV1 sequence; marketed as Iprivask). FDA-approved 2003 for DVT prophylaxis in hip replacement surgery.
- Destabilase
- Unique bifunctional enzyme with isopeptidase and lysozyme activity. Can cleave the isopeptide bonds that stabilize cross-linked (aged) fibrin clots, a mechanism distinct from plasmin-based thrombolytics. Crystal structure solved at 1.1 Å resolution (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). Of the approved DTIs, lepirudin and desirudin are recombinant hirudins and bivalirudin was designed partly on the C-terminal sequence of hirudin; argatroban is not leech-derived and dabigatran was designed from NAPAP.
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, taking a single large blood meal (up to roughly ten times body weight) that is digested slowly over several months.
- 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 salivary glands. Parent molecule of all DTI drugs.
- Hirudotherapy
- The clinical application of medicinal leeches (Hirudo spp.) for therapeutic purposes. FDA 510(k)-cleared as an adjunct to graft tissue healing when venous congestion may delay healing, or to overcome venous congestion by creating prolonged localized bleeding.
- 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 21, 2004). Cleared as an adjunct to the healing of graft tissue when problems of venous congestion may delay healing, or to overcome problems of venous congestion by creating prolonged localized bleeding; later clearances (K132958, K140907) use differently worded indications.
- 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 (Bayer discontinued production).
M
- Microsurgery
- Surgical specialty using microscope-assisted techniques. Medicinal leeches are FDA-cleared as an adjunct to graft tissue healing when venous congestion may delay healing, or to overcome venous congestion by creating prolonged localized bleeding.
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 (venous return is typically established by about postoperative day 5-7).
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 medicinal-leech salivary gland secretion (a powder in gelatin capsules, enriched with the leech's own proteinase inhibitors). 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 roughly 60–75% in rat carotid endarterectomy models. No approved pharmaceutical analog.
- SGS (Salivary Gland Secretion)
- The secretome of the medicinal leech salivary glands. Mass spectrometry identified 189 proteins in the salivary secretion of H. medicinalis (Babenko et al. 2020).
- 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 for which the medicinal leech is an FDA-cleared 510(k) device (K040187) in reconstructive 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.