We are in Australia and we have been doing the filter paper testing for about 3 years now for our 6 year old SWCAH daughter.  It works really well for her because it gives a reading over the whole day (6am, 12noon, 6pm and 11pm) and not just in the morning which was what we previously did when she had her blood drawn at the pathologist.   We simply prick her finger (same as a diabetic) and blot the blood onto the filter paper, refrigerate the paper and then post all 4 filter paper samples to the hospital the next day.  Very convenient and less stressful for our daughter.