The best way to diagnose your dog's illness is to take it to a veterinarian, according to Pet Health Network. The specific diagnostic methods vary depending on the individual dog, but they may include urinalysis and blood tests.
You can get some idea of what may be wrong with your dog by using a symptom checker, such as that created by PetMD. However, many symptoms can be signs of multiple diseases, according to WebMD. For example, if your dog is urinating more frequently, it can be a sign of diabetes, liver or kidney disease. Only further testing can determine the underlying cause.
Preventative care is also important for diagnosing canine illnesses, according to Pet Health Network. Dogs should generally see a veterinarian every year for a routine exam. The veterinarian may notice subtle signs of illness that you cannot see yet. Early diagnosis may help keep your dog from suffering and improve its chances of recovery. This practice also establishes a baseline for your individual dog, so if it does get sick, your veterinarian can tell what is wrong more easily.
If your dog has noticeable symptoms, consult with your veterinarian as soon as possible, suggests WebMD. Even if the symptoms are mild and related to aging, such as mild arthritis pain, your veterinarian may be able to help your dog and slow the progression of the disease.