Hyperthyroidism is common in older cats. It is caused when the cat's thyroid glands produce too many hormones. Symptoms often include weight loss, increased appetite and irritability. If you suspect your cat may have this condition, your vet can confirm it fairly easily.
The Physical Exam
The first thing the vet will do is give Fluffy a basic physical exam. This includes feeling her neck area to see if her thyroid glands are swollen. Usually the vet will feel a pea-sized enlargement, but occasionally the glands will feel normal. If her symptoms and the physical exam warrant it, the vet will order tests to verify the condition.
Testing T4 Levels
A physical exam is not enough to confirm hyperthyroidism. Often the vet will order a urine test to rule out other diseases (such as kidney failure). A blood test is necessary to determine the level of T4, a thyroid hormone that regulates metabolism. T4 is usually high in cats with hyperthyroidism, and this is often enough to confirm the disease.
When the T4 Test Doesn't Tell the Story
Some cats with hyperthyroidism can be difficult to diagnose, particularly if it is in the early stages. In these cases, the blood test will reveal a normal T4 level. T4 levels can vary over time, so the test may need to be run more than once. If T4 levels are normal, yet the vet still suspects hyperthyroidism, a T3 suppression test may be necessary. This test, which determines the level of another thyroid hormone, is more complex and requires the owner give the cat a pill three times a day for two days. After this, the cat gets a blood test. The final way to diagnose hyperthyroidism is a nuclear medicine scan, which will show the affected area very easily. However, the equipment necessary isn't always readily available to all vet clinics.
After the Diagnosis
Most cats with hyperthyroidism are fairly easily diagnosed. If Fluffy has been declared to be hyperthyroid, the tests will also help to determine how best to treat her. Hyperthyroidism is a disease that is fairly easy to manage—and may even be curable, depending on the treatment option you and your vet decide on.