CDC recommends prophylaxis only if the tick is engorged. In my country, guidelines do not recommend prophylaxis at all (for better or worse - personally, I would take a single doxycyclin dose for a >24h high-risk tick bite, Lyme is no joke).

However, guidelines universally recommend against testing ticks. For instance, IDSA says this:

> Knowing tick characteristics (ie, species, life stage, and an assessment of the degree of blood engorgement) is helpful for anticipatory guidance and in determining if antibiotic prophylaxis to prevent Lyme disease is appropriate [127]. Tick identification is available in most commercial laboratories and at some local health departments. Studies from the United States and Europe have shown that detecting B. burgdorferi sensu lato in Ixodes spp. ticks, however, poorly predicts either subsequent disease (0–12.4%) [126, 128–133] or asymptomatic seroconversion (0–4.7%) [126, 129, 130, 132, 134]. This is likely due to a variety of factors that influence the likelihood of transmission and the observation that most Ixodes spp. ticks discovered by patients have been attached for <48 hours [61, 62, 135].

(https://www.idsociety.org/practice-guideline/lyme-disease/)

The point is that the test is likely not useful to reliably inform any sort of prophylactic treatment, especially if the risk of transmission is high enough to warrant prophylactic treatment in the first place, in which case the PEP is indicated regardless of the tick test.

Sure, it modifies the prior probabilities, but what's the clinical significance of that?