when do labs matter?

dumb question ik but i've noticed that there have been questions on the nbme forms/free 120 where despite the diagnosis being so clinically obvious, i still choosing something other than the right answer because the corresponding lab values which should be abnormal are normal instead. if this was a set rule, i could just tell myself to ignore the labs when it's obvious, but then there's cases where the negative labs actually do play a part in getting to the right answer. including an example of two diff cases from the new free 120 below in spoiler text!

so basically tldr: in what scenarios (if any) should i just ignore the labs and go with my gut on the real deal? i'm really trying to trust my gut, but it's brutal out here being an anxious girlie 😭 😭

!for the gout question on the new free 120, serum uric acid levels were normal, but gout was still the right answer. then there was the hiv question presenting as acute mono where monospot was negative, effectively ruling out ebv. on the real exam, how can i differentiate between those two question types when looking at the labs to guide me? if it's obvious as hell like the gout question, should i just ignore the labs?!<