Yes, my son's doctor routinely asks for a 24 hr. urine sample to check for 17-ketosteroid levels, in addition to bloodwork. I don't believe he uses it to check renin on a regular basis. As far as I know, my son's renin level was only measured once, at the time of initial diagnosis, when it was determined that he was not a salt-waster. I am sorry that I cannot better explain what ketosteroids are, but as far as I know, they are essentially a measurement of metabolized androgens or male sex hormones. Since hormone levels change throughout the course of the day and bloodwork numbers seem to vary greatly depending on the time of day the sample was drawn and whether or not it was taken before or after meds., my son's doctor feels that the urine sample gives a better indication of whether or not a patient is actually well controlled, since it takes into account hormone levels over a 24 hr. period. Hope this helps!