Evaluation of renal function in hyperthyroid cats before and after I-131 therapy

cat exam
Area of Study: 
Internal Medicine

Purpose of Study: 

Hyperthyroidism is a very common condition of the older cat. It is caused by an overproduction of the thyroid hormone (T4) from a tumor (usually benign) of the thyroid gland, located in the neck near the trachea.

This disease usually results in weight loss, increased thirst, excessive urination, digestive problems, hyperactivity, and heart disease, but also is associated with abnormalities in kidney function.

Because thyroid hormone levels can have important effects on kidney function and because a large proportion of cats with hyperthyroidism also have pre-existing chronic kidney disease, most clinicians recommend assessing kidney function prior to treatment of hyperthyroidism. However, most markers of kidney function are not very sensitive.

A promising new marker, Symmetric DiMethylArginine (SDMA) has recently been shown to reflect renal function more accurately, in comparison to conventional measures (e.g. BUN, Creatinine). However, its accuracy in determining kidney function in cats with hyperthyroidism remains unknown.

The purpose of this study is: To investigate the utility of SDMA (via single blood test) as a marker of kidney function in hyperthyroid cats before and after I-131 treatment. We will evaluate how this test compares to the traditional measures of kidney function markers (BUN, creatinine, urine specific gravity) using renal scintigraphy.


Your cat may qualify for this study if he/she has been diagnosed with hyperthyroidism, and you and your veterinarian are interested in I-131 therapy to treat this condition. Your cat must have been off Methimazole (oral treatment for hyperthyroidism) for at least 10 days before the I-131 treatment.

Client Responsibilities: 

If you agree to enroll your pet in this study, it will involve 3 visits to the hospital over a 3 month period.

These visits are:

  1. The pre-treatment examination and I-131 treatment
  2. 1 month post-treatment recheck exam
  3. 3 month post-treatment recheck exam   

Note that pre-treatment evaluation of kidney function is routinely performed as part of our normal diagnostic workup, and that hospital visits at 1- and 3-months after treatment are routinely performed to assess patient status.

Each visit will require a blood pressure as well as blood collection to evaluate both thyroid status (T4) and kidney function (SDMA, urinalysis, renal profile: BUN and creatinine).

Renal scintigraphy (kidney scan) will also be performed on the day prior to I-131 administration (standard procedure) and at the 3 months post-treatment visit (specific to this study), since this test is the gold standard for measuring kidney function.

Scintigraphy is an imaging method that evaluates the function and anatomy of the kidney by using a small amount of a radioisotope. This procedure will require a brief period of sedation to accurately capture images. This procedure will only be performed if your cat is deemed a safe candidate for the sedative procedure.

For all visits at ISU, a veterinary internist and radiologist will oversee all procedures along with other specialists in the ISU Veterinary Teaching Hospital, as needed. 

Client Benefits: 

You will be compensated for all of the SDMA, renal blood tests, and T4 analyses costs, as well as for the two kidney scan procedures and blood pressure measurements.

You will be responsible for the costs of the routine urinalysis as well as for the cost of the technician visits, as they are part of routine costs for managing a cat with hyperthyroidism.


Dr. Al Jergens, 515-294-4900

Dr Jean-Sebastien Palerme, 515-294-4900