Haven't eaten much food, most food had gluten I think but today I only had a cucumber before celiac blood test, could lack of gluten give false neg?

Gluten testing. If avoided gluten for > 2 weeks, antibody testing may be negative since no antigen( culprit i.e. gluten) to cause the body to make antibodies . But 1 day of -no gluten -unlikely. Also can be gluten "sensitive/intolerant" and react to gluten-gas, anemia without celiac disease. Sometimes elimination of a food from diet is the best to see what is causing problems. f/u/ w/allergist.