A likely cause of foamy urine is proteinuria, or excessive protein in the urine, states Mayo Clinic. Excess protein in urine can indicate kidney problems or other serious ailments, notes Vetinfo.
Damage to or diseases of the kidneys and liver are common causes of proteinuria, but the condition can also indicate a urinary tract infection, notes Vetinfo. Urinary tract infections can alter the makeup of urine and cause high protein levels. Immune diseases that cause the body to attack its own tissue can also cause the condition, and cancer is a potential cause. Some cats are genetically more likely to develop this condition, as are diabetic cats and cats with Cushing's disease. Lungworm, heartworm and Lyme disease are parasitic diseases that can cause it.
Any additional symptoms the cat experiences depend on the cause, but they may include frequent urination, heightened water consumption, weight loss, decreased appetite, jaundice and agitation, states Vetinfo. A diagnosis of proteinuria requires urine analysis by a veterinarian and a comparison of protein to creatinine levels to determine severity. Additional tests are necessary to assess the underlying cause of proteinuria, and treatment depends on the cause. Cutting down on dietary protein helps cats with kidney damage.