I am not really sure if they can wait that long for the lytes to come back.  When they send filter papers away they go to a National Screening lab which is often not in your State whereas they can check electrolytes and blood sugar etc on site at the hospital labs and it needs a quicker diagnosis so that they can act.  I know that they checked the blood sygar last time at hospital with a glucose meter every now and again and they drew blood off to send to the lab to check for infection and also the electrolytes.  These tests tend to get priority over finding out what the 17 OH is which as far as I knew was the only thing they tested for where CAH is concerned.  They probably could check the lytes using that method but it will be no doubt decades away yet.  They can do cortisol and 17 OHp levels from saliva, but this also takes a while to get the results back.

For electrolytes you need the results back pronto.  When Ashley was diagnosed or whenever he has been sick and admitted they have done bloods and had the results for the lytes back more or less overnight.  At diagnosis they saw that the sodium was virtually nil and the potassium levels were very high.  The blood sugars also plummet in a crisis, so they can check those and diagnose adrenal insufficiency within a few seconds by just doing a prick with a glucose meter.  I would say they need to still get the electrolytes and check for infection though which can be done on site often within the labs there at the hospital.   They need to know what they are dealing with and how to treat asap.