左腎 is read as さじん (sajin) and means left kidney.
さじん
sajin
ひだりがわ
left side
さゆう
(serving at someone's) side
さよく
left wing (in soccer, rugby, etc.)
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
ひだりとう
left-wing party
さかん
plasterer
させつ
turning to the left
さは
left wing