Body substance isolation (or BSI) is a situation-dependent consideration in TCCC.
For example, in Care Under Fire, there is no time to worry about body substance isolation, although your tactical gloves do offer some level of protection. However, once in Tactical Field Care, whenever possible, responders should don latex-free gloves as a BSI precaution.
Gloves are found in most equipment kits, including the JFAK, CLS bags, and combat medic aid bags.