Yes.

Once, during dinner with some colleagues, I noticed something, but I just couldn’t figure out what! I was having fun, trying to have the “Diagnostic Mode” off. But the next day I remembered a moment during the dinner and that was that one of my colleagues had Hippocratic Fingers. It’s a change in the shape of the fingers:

(Not my pic; Source: Google images)

His case wasn’t so advanced (in fact it was quite subtle). I called him and pointed his attention to that fact and asked him to take a chest X-ray and an echocardiogram (clubbing of the fingers is due to poor oxygenation of the extremities). The most frequent etiologies are Pulmonary or Cardiac.

Turns out he had neither. He had a jaw bone tumor. It was caught relatively small and without metastasis. He underwent surgery and that was that. He is in follow-up (and will be for some years).

The bastard still owes me one dinner he promised for insisting that he was observed and tested and having the tumor caught so early! Eheh!

Edit - WOW, 1,3k upvotes! Thank you my fellow Quorans. But have in mind that I didn’t diagnose my colleague. But by finding a sign I pressed him into doing some exams and one thing lead to the other and he ended up being diagnosed. (As far as I know, the clubbing of the fingers had nothing to do with the jaw tumor. It was a “happy” coincidence to notice the clubbing and nagging him to do some tests).

Still, he owes me one dinner!