I don't think the allergy testing is wrong. Could it be that maybe his sensitivity level has increased? Or that your mom recently vacuumed and dusted before this time? Dog allergies are caused by their saliva and dander. And if someone has a dog but recently washes the dog, vacuums, dusts etc.....it can be easier on a dog allergy sensitive person. Allergies can occur at any time with no rhyme nor reason and they can go just as quickly or "outgrow" them. My son had severe dog allergies when he was little, we had to get rid of one dog but kept another that had wiry hair. His allergies lessened over time, until eventually I believe that his body built up enough antibodies to fight off his dog allergies. He is still sensitive to dogs but not as severely as before.
Ask your mom if perhaps she vacuumed, dusted or bathed the dog to see if that is why he didn't have a reaction before. Obviously you can't avoid seeing your mom, but have you tried Benedryl for those times that your son has to go over there? Or any other allergy med?
~Uc(Left-sided) since 1992 - Colazal, 6MP, Biotin, Forvia-In Remission~
~Secondary Raynauds Syndrome since 2004-Meds-Norvasc..Fibromyalgia since 2006, Acid Reflux - Prilosec OTC~
~~Help others such as yourself by donating to Healingwell, every penny counts!~~
@--->--Co-mod for Ulcerative Colitis...Moderator for Allergies/Asthma--<---@