What does it mean to dream about kidney?
A kidney often points to filtering and balance, the quiet work of clearing what the body does not need, and in old usage to a person's inner nature.
Four ways to read it
Each reading below comes from a named tradition and a cited source, so you can see where it came from and decide what fits your dream.
Freud
Freud would read the kidney as a hidden organ tied to the body's cleansing and to fears about inner health. Trouble there can stand for something the dreamer senses is amiss beneath the surface.
After Freud, The Interpretation of Dreams (Brill trans., 1913), public domain.Jung
Jung would see the kidneys as an image of inner sorting, the work of keeping what nourishes and letting the rest go. They may mark a need to clear away what no longer serves the self.
Jungian concept (our summary).Modern
Continuity ties the kidneys to waking concerns about health and the body's unseen upkeep. They tend to appear when a person has been anxious about wellbeing or has been told to take better care.
Continuity hypothesis (our summary).Mythological
Older traditions named the kidneys, or reins, as a seat of the inward self, the part searched by a god to know a person's true mind. To be tried in the reins was an old image of having one's hidden character weighed.
Rosmerta Publishing editorial synthesis (after Brewer; Bulfinch).