Hi.  I am hoping someone can help me with this question.  I have been diagnosed with MCAS but in preparation for an appointment with Dr. Castells, my doctor ordered a 24 hour urine test.  When I picked up the 'jug' (oh my!) from the lab, the instructions indicated that I should stop all antihistamines while doing the test.  Well, like most of you, I take a lot of antihistamines, including, Ketotifen, and I have been advised never to stop them.  So, I did the test and now am wondering whether the fact that I was on the antihistamines will affect the results?  I had a blood test for plasma histamine while still on the medications (except ketotifen) and it still showed elevated histamine.  Many thanks for your help.

Thanks Deborah!  Whew!  I was afraid it would screw up the results and I only have a very narrow window to get it done in the US before I leave.  The woman at the lab wasn't sure and just kept underlining the part that says 'no antihistamines etc etc' and the nurse in my allergist's office wasn't sure either so she put a note in the chart so that the results would be read in light of the meds I am on.  Unfortunately we have had a death in the family - a 4 year old who was having her 3 heart surgery - and so we are leaving the US early to attend her funeral.  Now that I know a little more, I am seeing the relationship between stress/upset and symptoms.  My doctor's office have been incredibly helpful getting stuff done in a hurry for me and best of all - I have an appointment with Dr. Castells when I return to the US in November.  Now to figure out this rash on the back of my neck.  I never have skin symptoms but now have a rough, irritated red patch on the back of my neck about 2inches by 1inch.  It's always something, isn't it!

Thanks for all of your help.  I am finding so much helpful info through this forum.