Hi Louise, After the short synacthen test, my son then had the long synacthen, whereby he is taken off his medication for for 5 days and given daily injections to stimulate the adrenal glands.  His ACTH levels were up in the thousands, yet it was not until the last day that we had any 17OHP reading and even then it was only about 30 - it should have been in the thousands too.  However this was progress, the adrenals were ’reactivated’ and when he had a 17OHP profile about a month later, he had reasonable levels of 17OHP. My son’s adrenal glands had probably been dormant for years though (probably since shortly after birth) and he was 13 years old by the time it was realised that apart from the initial 17OHP level to diagnose him, he had not had a level >1 since!  17OHP was not used as a measurement of control at the hospital he was under.  At that time he was on a very low cortisol level for his age (7.5mg daily), he also had a bone age that was 6 years delayed. 

Your son’s adrenals may have shut down too but it has been discovered much earlier.  They therefore may not take so much to get ’kick started’.  I actually sometimes wonder if my son would have been better off if we hadn’t gone to such lengths to re-activate them as he was able to exist on a much lower dose of hydrocortisone (treated more in line with Addison’s) and although 17OHP level was non-existant, he still produced average levels of testosterone for his age and it therefore didn’t affect pubertal development.

I think growth and weight can be difficult in a baby with CAH anyway - if your son is on a low dose of hydrocortisone, it shouldn’t be responsible for his poor growth and weight gain   Is his fludrocortisone dose adequate though?  My son’s initial growth was poor due to this - he did catch up though!

I think your son’s endo is probably right, wait for the DNA results and if is shows CAH, just continue to treat him and eventually the adrenals should just kick-start but until they do, he will no doubt be able to get by on a lower than normal dose of hydrocortisone for a child with CAH.  Sounds as if your son is well monitored for this to have been noticed so early, so I doubt you have anything to worry about and feel his height and weight will level out as he grows.