While true food allergies are rare, a natural diet can help some pets, and the food you are currently feeding is not one I recommend. Too many cats and dogs are placed on “prescription diets” when they really don’t need these and would be better served by a more natural diet devoid of by-products and chemical preservatives and additives. A better diet is always indicated even if the pet doesn’t get better simply by switching diets, as a better diet will go a long way to contributing to health and minimizing disease and reducing inflammation in the pet’s body. If your doctor suspects a food allergy, a feeding trial for 8-12 weeks must be done using a special diet (blood testing for food allergies, while often performed, is not accurate.)
Heavy consumption of the essential amino acid lysine (as indicated in the treatment of cold sores) has allegedly shown false positives in some and was cited by American shotputter C. J. Hunter as the reason for his positive test, though in 2004 he admitted to a federal grand jury that he had injected nandrolone.  A possible cause of incorrect urine test results is the presence of metabolites from other AAS, though modern urinalysis can usually determine the exact steroid used by analyzing the ratio of the two remaining nandrolone metabolites. As a result of the numerous overturned verdicts, the testing procedure was reviewed by UK Sport . On October 5, 2007, three-time Olympic gold medalist for track and field Marion Jones admitted to use of the drug, and was sentenced to six months in jail for lying to a federal grand jury in 2000.