My 24-hour urine histamine is in the middle of the reference range.  My doctor wants me to take Xyzal (5 mg.) and Zantac (75 mg. am and pm) initially.  I am going to take 2.5 mg. of Xyzal in the morning and 2.5 mg. at bedtime.

Why would antihistamines help me if my histamine levels are normal?

At what point have your doctors added mast cell stabilizers to the antihistamine regimen?

There is also the possibility of a false negative as well as that of chronic release of histamines versus acute histamine release.  

Yet there are also recognized problems with the testing in that the researchers don't understand why we don't all show positive tests.  It could be that you do have histamine release going on and one 24 hr reading won't show it.  You need to do several for histamine has a very short time span that it's within the system.  So, just because you didn't find it on this one reading doesn't mean it's not going on.  I f you respond well to the meds, this is an important indication that you are releasing histamine into your system.  

Buster, the researchers still can't figure it all out yet.  They have found some IA patients who have negative markers for masto ended up having the defect upon their mast cell, but in all other ways of trying to find the disease, their tests totally failed!  The researchers will openly admit that there are too many patients falling through the diagnostic cracks and now they are finally recognizing that this is likely due to the testing not being specific enough.  Thus they keep seeking for more understanding and better, more reliable markers.

Lisa