I take 325 mg aspirin for clotting disorder. i had a toxicology screen done once in hospital and it showed my salicylate level was undetectable. not in therapeutic range. does this mean i am aspirin resistant and i need different anti platelet ?

Aspirin is processed out of the body at different rate depending on personal metabolism. Achieving an acceptable salicylate level depends on the dosing interval (often every 6 hours) and the dose (often more than a single 325mg). I have had kids that needed 2 tablets every 6 hours to stay in a good range. Using enteric coated aspirin (Ecotrin) can avoid some of the stomach irritation.

Aspirin at 325 mg/day is below the therapeutic range for pain control. This dose is sufficient to inhibit platelet function. It is unlikely that you are aspirin resident. Talk to your doctor to ascertain if you should be taking aspirin. It has undesirable side effects that may outweigh the benefits. Wish you good health!