How to read the Condition Atlas
A reader’s guide to the 199-condition catalog and the Tier A/B/C evidence system.
The Condition Atlas is a catalog of 199 conditions that appear in the medicinal-leech therapy literature. It exists for education and research orientation, not for treatment guidance. Each entry classifies the published evidence into one of three tiers — Tier A, Tier B, or Tier C. This page explains how to read those tiers, and, just as importantly, what each tier does not mean.
A catalog, not a treatment plan
Listing a condition in the Atlas describes the state of the published evidence for that condition. It is a bibliographic and regulatory map. A catalog entry is not a treatment claim, a recommendation, or a statement that hirudotherapy works for that condition. The tier is a description of evidence quality — it is not a ranking of how strongly any use is advised.
Nothing in the Atlas asserts a cure, guarantees a benefit, or substitutes for the judgment of a qualified clinician who knows an individual patient. Read every entry as “here is what the literature says,” never as “here is what you should do.”
The three tiers, and what they do NOT mean
Every condition in the Atlas carries one tier badge. Here is how to read each one.
FDA-cleared device-indication context
What it means: the entry sits within the context of the FDA device clearance for Hirudo medicinalis (K040187, June 21 2004) for venous congestion in surgical flaps. This is the only formally cleared indication, and Tier A flags that regulatory context.
What it does NOT mean: Tier A does not mean “cure,” and it does not mean leech therapy is first-line for everything. The clearance is narrow and surgical; it says nothing about the many other conditions in the catalog.
Off-label, RCT-supported
What it means: there is at least one randomized controlled trial or systematic review in the published literature for a use outside the FDA-cleared indication. The entry summarizes that evidence.
What it does NOT mean: Tier B does not mean the use is FDA-approved, endorsed, or recommended by ASH. “Off-label” means exactly that — any such use is an individualized clinical decision made under informed consent, not a blanket recommendation.
Investigational / early evidence
What it means: the entry rests on mechanistic rationale and limited human evidence — case series, small pilots, or preclinical extrapolation. It is cataloged so researchers can find it, not because it is established.
What it does NOT mean: Tier C does not mean proven, effective, or safe for that use. Early-stage evidence is hypothesis-generating; it is the beginning of a research question, not an answer.
What a tier does NOT mean (summary)
- A tier is not a treatment recommendation — it describes evidence, not advice.
- A higher tier does not mean a stronger recommendation; it means a different kind of evidence exists.
- No tier on any entry asserts a cure or a guaranteed benefit.
- Tier A (FDA-cleared context) does not make leech therapy first-line for other conditions.
- Tier B (off-label, RCT-supported) does not mean FDA-approved or endorsed.
- Tier C (investigational) does not mean proven, effective, or safe for that use.
- Listing a condition in the catalog is not a claim that hirudotherapy works for it.
Reading an entry in practice
- Start with the tier badge. It tells you what kind of evidence exists, so you can calibrate how much weight the literature carries.
- Read the “does NOT mean” framing on every Tier B/C entry. Each condition page carries an explicit boundary box clarifying evidence limits in plain language.
- Check the citations, not just the conclusion. The Atlas links to the underlying PMIDs so patients and researchers can read the primary sources directly.
- Take questions to a qualified clinician. The catalog informs a conversation; it does not replace individualized medical advice.
Related pages
Conditions Registry
The searchable list of individual condition entries and their citations.
Browse conditions →How Evidence Is Graded
The full Tier A/B/C framework and GRADE-aligned ratings behind every entry.
Read the method →