I make diagnoses from tissues (biopsies, surgical specimens) and fluids (e.g. Pap smears, blood drawn from a vein).
Occasionally, it involves doing autopsies, but people seem to be most interested in that.
Here's a view of a breast biopsy from a woman who felt a lump and had a suspicious mammogram:
Looks like cancer... but it's not, so a benign diagnosis saves this lady from the complications of a lymph node dissection.
