They can hear, remember and react. Consequently in my almost 40 years of practice, I've made the habit of never saying anything in the presence of a comatose patient that could hurt her or come back to haunt me. On many occasions, I've been grateful for that lesson learned. However, the test is so cumbersome that many people prefer to avoid it. Furthermore, a basal temperature may be low because of other factors.
Blood tests are quicker and more accurate.
In my opinion, blood tests are the way to go. Basal temperature recordings have largely been confined to women who need to know the time of ovulation so that they can become pregnant.