Thyroid Profile: How T3, T4 and TSH Fit Together
Short answer
A thyroid profile measures T4 and T3, the thyroid hormones, and TSH, the pituitary signal that drives them. Read together, the three help a vet see whether a dog's or cat's thyroid is too slow, too fast or normal.
By Pashupatinath Vet Lab Share
A thyroid profile measures three things in the blood. T4 and T3 are thyroid hormones, and TSH is the signal from the pituitary gland, a small gland under the brain, that tells the thyroid to work. Read together, they help a vet see whether the thyroid is too slow, too fast or normal. A registered veterinarian interprets the results.
What does the thyroid do?
The thyroid is a pair of small glands lying on either side of the windpipe in the neck. Its hormones set how fast the body uses energy. Too little hormone slows things down, and too much speeds everything up. Weight, skin, hair, heartbeat and temperament all respond.
How do T4, T3 and TSH fit together?
Think of the pituitary as a thermostat and the thyroid as a heater. When hormone levels fall, the pituitary raises TSH to push the thyroid harder.
- A T4, Total result shows the main hormone the thyroid releases. Most of it travels attached to proteins in the blood.
- T3 is the more active form, and the body makes much of it from T4 in the tissues.
- A TSH result shows how hard the pituitary is pushing.
The Thyroid Profile (T3, T4 & TSH) groups all three on one serum sample. A low T4 with a high TSH points towards an under-active thyroid. A low T4 with a TSH that is not raised settles little, because other illnesses and some medicines can lower T4 without any thyroid disease. That is why vets seldom decide from one number.
Why do dogs and cats differ?
In dogs the usual worry is an under-active thyroid. Typical signs are weight gain without eating more, tiredness, a dull coat with thinning hair, skin trouble and a dislike of cold. The Dog Thyroid Check Panel typically adds cholesterol and a blood count to dog-specific T4 and TSH, because cholesterol can run high when the thyroid is slow. An over-active thyroid is rare in dogs.
In cats it is the other way round. An over-active thyroid is common in older cats, with signs such as weight loss despite a good appetite, restlessness, extra thirst and vomiting. The Cat Thyroid & Kidney Check typically adds kidney, sugar and blood count checks to cat T4, because older cats can have kidney disease at the same time. An under-active thyroid is uncommon in cats. The exact list in either package is confirmed when you book.
What is a free thyroid profile?
Most T4 in the blood is attached to proteins, and only a small part floats free and can enter the tissues. The Free Thyroid Profile (FT3, FT4 & TSH) measures that free part of T3 and T4, along with TSH. A vet may choose it when the usual results are hard to interpret, for example when a pet has another illness. Tell your vet about every medicine and supplement your pet has had, because some can change thyroid results.
How should owners treat the numbers?
A thyroid number is a clue, not a verdict. A pet that is unwell with another condition can show a low T4 without thyroid disease, so a vet may repeat the test after some time or add another one. Please never give thyroid medicine or supplements on your own. They act on the heart, and wrong use can harm. If treatment is needed, the vet plans it.
If treatment is started, the vet may recheck the hormone levels from time to time to see how the pet is responding. Vets also often add a T4 check to the routine tests of older cats. Show your pet to a vet promptly if it is losing weight, drinking a lot or growing unusually sluggish, and do not wait for a scheduled check.
Read next
For a closer look at the signs of an under-active thyroid in dogs and the tests a vet may ask for, read Thyroid Problems in Dogs: Signs and Tests Explained. If you also care for dairy animals, Mastitis Testing: CMT, Cell Count, Culture and RT-PCR shows how a step-by-step testing ladder works for udder infections.
Testing in Bhopal
Thyroid tests use serum, so a small blood draw is all that is needed. Call or WhatsApp +91 88175 01118 to ask for free sample collection anywhere in Bhopal, or bring the sample to C-200, C Sector, Shahpura. If you live outside Bhopal, your vet can send it by courier or bus parcel, and the lab confirms the method, sample needs and reporting time when you book.
This article is general information and does not replace a veterinarian’s advice. Please talk to a registered veterinarian about your animal’s signs, tests and treatment.