Differential diagnosis between iTTP and VITT
| Disease . | iTTP . | VITT . |
|---|---|---|
| Presenting symptoms | Variable with frequent neurological presentation* | |
| Platelets | Severe thrombocytopenia (frequently <30 × 109/L) | |
| Microangiopathic hemolytic anemia | Present: low hemoglobin, LDH elevation, undetectable haptoglobin, schistocytes on blood smear | Usually absent† |
| Anatomical distribution of thrombosis | Microvascular | Macrovascular |
| D-dimers | Usually <4000 FEU | Usually >4000 FEU |
| Fibrinogen | Within normal range or slightly increased | Usually decreased |
| Specific diagnostic tests | ADAMTS13 <10% | Anti-PF4 antibodies |
| Anti-ADAMTS13 antibodies | ||
| Type of vaccine‡ | No increased incidence observed with any COVID-19 vaccines | Adenoviral vector–based |
| Disease . | iTTP . | VITT . |
|---|---|---|
| Presenting symptoms | Variable with frequent neurological presentation* | |
| Platelets | Severe thrombocytopenia (frequently <30 × 109/L) | |
| Microangiopathic hemolytic anemia | Present: low hemoglobin, LDH elevation, undetectable haptoglobin, schistocytes on blood smear | Usually absent† |
| Anatomical distribution of thrombosis | Microvascular | Macrovascular |
| D-dimers | Usually <4000 FEU | Usually >4000 FEU |
| Fibrinogen | Within normal range or slightly increased | Usually decreased |
| Specific diagnostic tests | ADAMTS13 <10% | Anti-PF4 antibodies |
| Anti-ADAMTS13 antibodies | ||
| Type of vaccine‡ | No increased incidence observed with any COVID-19 vaccines | Adenoviral vector–based |
FEU, fibrinogen equivalent units; PF4, platelet factor 4.
As cerebral venous thrombosis represents the most common location of macrovascular thrombosis during VITT.
Overt signs of microangiopathic hemolytic anemia should argue in favor of iTTP over VITT. However, theses biological variables are rarely mentioned in VITT reports; therefore, their true prevalence is unknown in such condition.
As triggering factors for iTTP vs etiological agent for VITT.