Do I need to boil kidneys?
It's perfectly safe to eat kidneys unwashed. But almost nobody enjoys smelling ammonia, urea or nitrogenous wastes in general when eating food.

You can boil them to remove that taste.

But a better alternative is to leave them covered with salt in a colander (so what everybody thinks there's in kidneys for a moment  will fall off). Leave there for about two hours, and then rinse them with water with vinegar.



Source: I asked a nephrologyst who prepares one of the best Riñones al Jerez (in English kidneys in Sherry) I've ever tasted.