Is this test being done specifically to pinpoint oversuppression, or to monitor overall control?  A more comprehensive panel is generally suggested if it is the latter, but if you are JUST trying to confirm oversuppression, I think you can make the argument that it may be enough. 

 

We normally test urine, but once our doctor made a similar comment about blood being more useful for assessing overtreatment, while urine was more useful for assessing undertreatment.  It took me awhile to figure out what he meant by that, but I think it is this:  Basically, if you take blood when ACTH is high in the morning, one would expect that 17-OHP levels would be physiologically high, in response to the high levels of cortisol. If levels are low, in spite of this universal phenomenon, I think it would be very reasonable to conclude that one is being overtreated.  This would only apply, though, to a situation if the test was done in the morning, BEFORE medication, and close to when ACTH levels peak ~8AM.

 

Depending on why you suspect oversuppression, if your child is a salt-waster, a renin number might also be indicated, since one can, apparently, become overtreated with florinef, as well.   Too much florinef will, presumably, not result in the same problems as too much cortisol, but, apparently, it can also result in problems with slow growth.

 

The "nice" thing about overtreatment is that it gives you lots of visual cues, so you can look for those, as well.  In spite of what the numbers say, if there are problems with moon face, disproportionate weight gain, excessive body hair, slow growth, etc. I think there is good reason to question whether oversuppression might not be a problem.  Good luck!