Sometimes they may only run 17 OHP when things appear to be well.  They run a battery of tests when they need to double check the 17 OHP result at times, i.e. when it is too high.  They can check if other hormones are being made after 17 OHP in the metabollic pathway just to make sure it’s not some glitch before they decide to raise the dose.  They will raise the dose if the raise in 17 OHP and the other hormones that follow are persistantly raised above more than one test--or should do.  They may also check these if they feel the child may be a tad over treated.  17 OHP will indicate either scenario--over or under treated.  Often though they need to double check because 17 OHP could be temporairly raised or lowered for several reasons and not necessarily anything to do with either over or under treatment.  I.e. illness and double or triple dosing a few days before blood draw or week before which lowered 17 OHP.  Or maybe illness that was quite out of hand and where 17 OHP levels were still left at very high levels, even after double or triple dosing.    Our sons last Doctor said he worked in this way, but of course the battery of tests he was supposed to do when there were problems never materialised.  But it is a feasible way to control things used effectively.  I.e. when the 17 OHP is out of the normal ranges and until it drops back into the normal ranges.  Renin may only be run 6 monthly also in most cases.