 One hypothesis is the poisoned cat foods might have higher concentrations of melamine than the dog foods.Melamine can be detected in blood or urine tests.Stephen Sundlof, director of the FDA's Center for Veterinary Medicine, says "Melamine is not very toxic as a chemical, so we're wondering why we are seeing the kinds of serious conditions, especially the kidney failure, that we're seeing in cats and dogs... We are focusing on the melamine right now because we believe that, even if melamine is not the causative agent, it is somehow associated with the causative agent, so it serves as a marker".