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Causality: well established
Causality assessment · Causality: well established
Heparin and Heparin-induced thrombocytopenia (HIT): is the FAERS signal real?
A written Bradford Hill assessment of one drug–event pair. The grade is a judgement about the signal, not a statement that this drug causes this event in any one person; FAERS counts are reports, not rates.
Heparin ↔ Heparin-induced thrombocytopenia (HIT)
n=1,273 co-reports · PRR 533.2 · ROR 587.8
Heparin-induced thrombocytopenia is a distinctive, immune-mediated reaction in which antibodies to the heparin–platelet-factor-4 complex activate platelets, causing a falling platelet count that paradoxically predisposes to thrombosis. It is a genuine drug-specific effect, typically appears 5–10 days after starting heparin, and requires immediate discontinuation and a non-heparin anticoagulant. The very high PRR (533.2) reflects that the term itself is essentially heparin-specific, so it reports back to heparin almost by definition.
Regulatory basis: heparin prescribing information (HIT warning; platelet monitoring). Established HIT immunoassay literature.
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | Falling platelets appear 5–10 days into exposure and recover after heparin is stopped |
| Strength | met | Very high PRR, but partly because the coded term is heparin-specific by name |
| Consistency | met | Reproduced across unfractionated and low-molecular-weight heparins |
| Specificity | met | Distinctive antibody-mediated syndrome tied to the drug–PF4 complex |
| Biological gradient | partial | Risk varies with heparin type, duration, and patient group; not a simple dose gradient |
| Plausibility | met | Anti-PF4 antibody-mediated platelet activation is the defined mechanism |
| Coherence | met | Coheres with routine platelet-count monitoring during heparin therapy |
| Experiment | partial | Consistent with controlled studies of switching to non-heparin anticoagulants |
| Analogy | met | Analogous to HIT-type reactions with other heparinoid anticoagulants |
This page's own qualitative read, not an automated/citation-gated assessment.
✗ The results-posting trial that surfaced (anticoagulation in cancer, NCT03045406) compared apixaban with the heparinoid dalteparin and recorded a single HIT event, on dalteparin — too few to characterise. HIT is rare and detected through routine platelet monitoring, not trial AE tables.