Table 1.
Comparison of COVID-19 and HIT.
| COVID-19 | HIT | |
|---|---|---|
| Similarities | ||
| Risk of severe disease | 1–5% (?) infected patients develop severe disease | 1–5% heparin-exposed patients develop HIT |
| High frequency of thrombosis | ~40–50% of ICU patients | ~40–50% thrombosis rate |
| Higher frequency of thrombosis with greater disease severity | Thrombosis rate higher in ICU versus ward patients | Thrombosis rate higher in patients with more severe thrombocytopenia |
| Venous versus arterial thrombosis | Venous predominance | Venous predominance |
| Arterial thrombosis hierarchy | Stroke > MI > limb | Limb > stroke > MI |
| Occurrence of unusual thrombi | Yes (e.g., CVST, mesenteric artery or vein) | Yes (adrenal, CVST, mesenteric artery or vein, etc.) |
| Endothelial activation | Yes | Yes |
| Neutrophilia | Yes | Yes |
| Leukocyte activation | Yes | Yes |
| Differences | ||
| Prominent thrombocytopenia | No (mild thrombocytopenia common); moderate to severe thrombocytopenia occurs in some patients with fatal COVID-19 | Yes (>50% platelet fall in ~90% of patients with HIT; median platelet count nadir, 60–70 × 109/L) |
| In situ pulmonary thrombosis | Common | Uncommon |
| ARDS picture | Common | No |
| Pathological criterion indicating risk for thrombosis | No distinct marker for risk for thrombosis | Platelet-activating HIT antibodies detectable by platelet activation assay |
| Thromboprophylaxis and treatment consensus | No consensus re: anticoagulant dosing | Therapeutic-dose anticoagulation generally recommended (even in the absence of documented thrombosis) |
Abbr.: ARDS, adult respiratory distress syndrome; COVID-19, coronavirus disease, 2019; CVST, cerebral venous sinus thrombosis; ICU, intensive care unit; HIT, heparin-induced thrombocytopenia; MI, myocardial infarction.