左腎 is read as さじん (sajin) and means left kidney.
さじん
sajin
さう
(serving at someone's) side
さそく
left side
さよく
left wing (in soccer, rugby, etc.)
さようなら
farewell
ひだりて
left hand
さわん
left arm
ひだり
left
ひだりきき
fondness for alcohol
させん
demotion
さとう
left-wing party
さかん
plasterer
させつ
turning to the left