I believe that bone-age advances are due to sex hormone levels, basically testosterone and estrogen. Before a child reaches puberty, those hormones come mostly from the adrenals. The steroid medicines, e.g. hydrocortisone, that CAH children take, are for control of the adrenals. Endos look at a number of different hormone levels---notably 17OHP, androstenedione, and testosterone---to determine whether or not a patient is under good control. They are all related to each other. I think if one number goes down, theoretically the other ones should, too, but I believe that it is the testosterone level that is actually the determining factor in advancing bone age. Once a child reaches puberty, though, even if the adrenal glands are under good control from the meds., the sex hormones start getting produced in the reproductive organs,as well, i.e. testes in boys, ovaries in girls. These also, then, need to be well controlled if bone age is to be kept from advancing. In boys, some docs use visual measures to determine if puberty has started, by measuring the size of the testicles. Others apparently use ultrasounds. I believe the most reliable way is to do a blood test called an LHRH test. This determines if puberty has started chemically, even if it may not have appeared to have started physically. If it is determined that puberty has begun, then docs will usually prescribe Lupron, a monthly injection which halts the pubertal process. So basically, to stop bone age from advancing, both adrenals and gonads have to be well controlled. Sorry to go on for so long, and hope this helps. I have been very lucky to have had an endocrinologist who has been patient enough to share information with me, and explain the medical and scientific reasons for why things are done. I wish more doctors were like him, and realized that if patients and their families were able to understand exactly what was going on, we would actually end up with a lot fewer questions in the end.