My son who is just approaching his 13th birthday has had annual bone ages taken since he was diagnosed at 2 weeks. We are aware that the bone age result can have an "error" of 6 months in either direction, but have used them in conjunction with the blood tests. They have proved to be invaluable not only to assess medication changes, but for the orthodontist when Mark had to have braces - the bones give a good indication of teeth maturity .