Dear Brighton Collaboration members:
Please find below a draft Brighton Collaboration case definition for both TTS (thrombosis and thrombocytopenia syndrome) and VITT (vaccine-induced thrombocytopenia and thrombosis).
The online review survey will ask about each case definition level of certainty (TTS and VITT) separately. The proposed TTS case definition is a revision of the version posted to the Brighton Collaboration website in Nov 2021.
There are two reasons for having two separate case definitions.
- The VITT CD is very specific and laboratory-test-oriented. It may not be feasible to apply in some settings where anti-PF4 antibody or D-dimer cannot be measured. It is possible to reach level 3 of VITT without either but any missing clinical or investigative information needed for other VITT criteria could make it difficult to meet any level of certainty. VITT is actually one of the syndromes that falls under the TTS umbrella. Others include TTP (thrombotic thrombocytopenic purpura), HIT (heparin-induced thrombocytopenia) syndrome, and APLS (anti-phospholipid syndrome). If a suspected case of VITT cannot meet any level of certainty for the case definition, it can be assessed against the TTS case definition which is more easily applied in low-resource settings.
- Entities other than VITT fall under the TTS umbrella, and some of these have been reported as being temporally associated with vaccination (TTP, APLS). The TTS CD can be used to classify all the entities without a need for specific laboratory testing. As such it can provide a temporary case ascertainment tool if there is a new safety signal with thrombocytopenia and thrombosis syndrome.