A "stab lab" is a plasma
donation center, such as those run by the Alpha Therapeutic Corporation
. The name refers to the needle
which is stuck in donors' arms for an hour or so each visit.
Ironically, I have most often heard this derisive term used by youths who sell their plasma for beer money.
(To be fair, donated plasma is used for therapeutical products which are vital in saving the lives of many hospital patients. Don't get me wrong - it's just the impersonal, often careless and exploitative method of extracting the plasma that some people have a problem with.)