florinef and skin testing

my daughter has postural orthostatic tachycardia syndrome/chronic fatigue syndrome.  she has been on Florinef for about 4 months.  her dose at first was 0.1 mg and 4 weeks ago it was increased to 0.2 mg once a day.  
Yesterday we saw an allergist/immunologist.   they did skin testing on her.  when they injected the histamine(?) into her arm for a test dose, she reacted.  it itched and turned red and a small weal appeared.   when they did the full skin testing - all over her back - nothing reacted, not even the control.  Could the Florinef cause this?  he wants to do some other immunological blood work, would it be helpful if she's on the florinef?  
thanks so much for your time.  
rbird

[National Jewish Health]

It is unlikely that the skin tests were negative because of the Florinef® (fludrocortisone), since she reacted to the histamine, which is the positive control.  The control that she did not react to would most likely have been the saline, which is the negative control.