Could it be a medical problem?
One of the first steps to determining why a cat urinates or defecates on our carpet or bed is to determine whether there is a medical problem.
Your pet's doctor can perform a good physical exam and laboratory tests to diagnose diseases that cause our cats to eliminate outside the litter box, such as diabetes, hyperthyroidism, feline lower urinary tract disease, cancer, neurological disease, intestinal parasites or constipation. Age-related diseases, such as arthritis or impaired cognitive functions, can also influence our cat's ability to get to the litter box in time.
Could it be the litter or the litter box?
Sometimes cats will urinate or defecate outside of the box simply because the box, the litter or the location of the box is not acceptable to them. The box may have an offensive odour because it was cleaned with a harsh chemical. Or, if the box is not cleaned often, the box may smell of urine. (It's recommended that you have two litter boxes for one cat, three boxes for two cats, etc. and clean them daily). Often cats find the texture of some litter distasteful and have a preference for fine or coarse litter, clumping or non-clumping litter. While scented litter appeals to us, many cats find the perfume unsavoury. Also, the location of the box can play a role. For example, the box may be in a high-traffic, noisy, dark or dank area. Or your cat is afraid to use the box because she was terrorised while she was in the box or ambushed as she tried to exit the box (thus, don't capture your cat to give medications while in the litter box).