Examining people's blood. Or their pees. Or their poops. And sometimes things even much more viscous, rank, and foul. Medical labwork falls under the greater umbrella if Pathology; the study of how illness is propagated within and affects the body.
This means primarily doing tests on these bodily fluids to help gather the information that helps a doctor diagnose what has happened to someone or to track their recovery.
In contemporary practice, there are a lot of machines and analyzers that help carry out these tests. So being a modern lab scientist is sort of like being half-engineer and half-assembly line worker. With some occasional "old-fashioned" stuff sprinkled in, like looking at things under microscopes, doing manual tests on your bench top with beakers and test tubes, or mixing blood and antisera together to see what happens.
Medical lab science! ❤️ Examining people's blood. Or their pees. Or their poops. And sometimes thin