There's even a wikipedia entry: Lab lit, which states Lab lit is a genre of fiction that centres on realistic portrayals of scientists, and science as a profession.
Let's take a step back. What exactly is science fiction? I interviewed one of the world's foremost experts on this in 2007. James E. Gunn said, Science fiction is the literature of change; science fiction is the literature of the human species; science fiction is a (note not "the") literature of ideas. If I had to choose one, slightly longer, it would be: Science fiction is the literature of the human condition experiencing meaningful change.
So, does lab lit fit into this definition? Yes?
As a speculative fiction editor, the question of a story's genre does come up from time to time. I must admit if a story could all be true, I reject it as not speculative fiction. Of course, truth in science is a moving target. Faster-than-light neutrinos would be science fiction. Higgs bosons would not be science fiction.
So, what do you think? Is lab lit a genre? Is it separate from science fiction? I'm undecided...