Cytology
From Memory Alpha, the free Star Trek reference.
Cytology is the branch of biology the deals with the structure, function multiplication pathology and life history of cells.
In 2371, the Doctor was required to do a complete pyrocyte replacement to the sole survivor of a Kazon raider in order to keep him alive. In preparation of the procedure, Kes offered to run a cytological screening of USS Voyager's crew in order to find a compatable donor. (VOY: "State of Flux")
