Most ped endo in the United States (trained in the US) do blood work vs the urine test. When I asked why... they said it was too much trouble to collect (especially for an infant) and not as accurate.

The plasma renin blood test need to be taken. Plasma renin is a blood test that reflects blood volume and therefore is very useful in determing the adequacy of mineralocorticolid replacement in primary (or classical) CAH adrenal insufficiency. Cortef and Florinef are mineralocorticoid and glucocorticoids replacement drugs. When these are low... the blood pressure is low which can lead to adrenal crisis or shock and death.  The child is very sleepy, dizzy, weight loss, dark skin or dark circles under the eyes. Difficult symptoms to spot in a infant or small child.

If the plasma renin blood test is too high (it should be very low... 0 or 1..2, etc) then then child is not getting enough drug replacement or been ill... or not enough salt in the diet (usually in an infant and the doctor did not prescribe enough salt in the diet) - and it affects the mineralocorticoid and glucocorticoids (mostly the mineralcorticoid or florinef medication) levels.

The 17-OHP blood test..is the most important (done between 6 and 8 am without the morning meds and it send to endo lab in CA). Adrenal gland  deficiency results in the accumulation of precursor steroids such as 17-hydroxyprogesterone as well as abnormal levels of other steroid hormones, specifically increasing androgens and decreasing glucocorticoids.  Other steriod hormone blood tests that my ped endo doctor orders - testosterone and adrostenedione.

The annual bone growth x-ray is important too. (most agree start looking at it at age 3). And chart growth and weight (at any age).

I personnaly disagree with doctors that just prescribe the meds without looking at the all blood work or go only by body mass or growth. How do you really KNOW the medications are working. And if CAH is not properly managed the child with not grow to proper height and fertility problems that can not be fixed (no magic wand... even with growth shots or more hormones)... and not to mention possible death from an adrenal crisis!!!