T4 Thyroid Testing for Dogs and Cats

What is a T4 test for pets?

A T4 test (thyroxine test) is a simple blood test used to evaluate your pet’s thyroid function. The thyroid gland plays an important role in regulating metabolism, energy levels, weight, and overall health.

This test is one of the most common and effective ways to screen for thyroid disease in both dogs and cats.

Why is T4 testing important?

Thyroid conditions are common in pets and can significantly impact their quality of life. A T4 test helps detect these issues early so treatment can begin as soon as possible.

  • In dogs, T4 testing is primarily used to diagnose hypothyroidism (low thyroid levels)

  • In cats, it is most commonly used to diagnose hyperthyroidism (high thyroid levels)

Signs your pet may need a T4 test

In dogs (possible hypothyroidism):

  • Weight gain without increased appetite

  • Low energy or lethargy

  • Hair loss or thinning coat

  • Dry skin or recurring skin infections

In cats (possible hyperthyroidism):

  • Weight loss despite normal or increased appetite

  • Increased vocalization or restlessness

  • Vomiting or diarrhea

  • Increased thirst and urination

What to expect during the test

A T4 test is quick and minimally invasive:

  • A small blood sample is taken from your pet

  • Results may be available the same day or within a few days

  • No anesthesia is required

In some cases, additional thyroid testing (such as free T4 or a full thyroid panel) may be recommended for a more accurate diagnosis.

Understanding your pet’s results

  • Low T4 in dogs may indicate hypothyroidism

  • High T4 in cats is often diagnostic for hyperthyroidism

Your veterinarian will interpret results alongside your pet’s symptoms and overall health to determine the best next steps.

When should your pet be tested?

We may recommend T4 testing if your pet:

  • Is showing symptoms of a thyroid condition

  • Is a senior pet (routine screening)

  • Has unexplained weight or behavior changes

Schedule a thyroid test for your pet

If you’ve noticed changes in your pet’s weight, energy, or behavior, a T4 test can provide valuable answers.

Contact our team today to schedule an appointment or learn more about thyroid testing for your dog or cat.