Thursday, June 11, 2015

Diagnosing Hypothyroidism in Dogs

I have a 7-year old spayed Golden Retriever who weighs about 110 lbs. No signs of hypothyroidism except for being overweight with a borderline high serum cholesterol concentrations (256 mg/dl). The serum T4 value was slightly low at 0.9 µg/dl (reference interval, 1.0-4.0 µg/dl).

Is this slightly low serum T4 concentration diagnostic for hypothyroidism? Would you start her on levothyroxine (L-T4) and retest T4 levels in a month?

I'd appreciate your thoughts and recommendations.

My Response: 

I would never base the diagnosis on only a resting serum T4 value alone. We commonly find low values that fluctuate in and out of the reference range in dogs that are clinically normal and never develop hypothyroidism. In addition, most non-thyroidal illness will lower the total T4 values in dogs, and these dogs would not benefit from thyroid hormone supplementation (1). It certainly doesn't sound like your dog is sick or acting ill in any way, so this latter explanation probably doesn't apply here.

For your dog, I'd recommend that your veterinarian collect more sera to do a complete thyroid panel, which should include the following tests (2-4):
  • Serum T4 concentration
  • Serum T3 concentration
  • Serum free T4 by dialysis
  • Serum TSH concentration
  • Serum levels of thyroglobulin autoantibodies
If you have it available in your area, thyroid scintigraphy (nuclear medicine scan) is actually the best and most accurate way to diagnose hypothyroidism in dogs (4.5).

  1. Kantrowitz LB, Peterson ME, Melian C, et al. Serum total thyroxine, total triiodothyronine, free thyroxine, and thyrotropin concentrations in dogs with nonthyroidal disease. J Am Vet Med Assoc 2001;219:765-769. 
  2. Peterson ME, Melian C, Nichols R. Measurement of serum total thyroxine, triiodothyronine, free thyroxine, and thyrotropin concentrations for diagnosis of hypothyroidism in dogs. J Am Vet Med Assoc 1997;211:1396-1402.  
  3. Nachreiner RF, Refsal KR, Graham PA, et al. Prevalence of serum thyroid hormone autoantibodies in dogs with clinical signs of hypothyroidism. J Am Vet Med Assoc 2002;220:466-471. 
  4. Diaz Espineira MM, Mol JA, Peeters ME, et al. Assessment of thyroid function in dogs with low plasma thyroxine concentration. J Vet Intern Med 2007;21:25-32.  
  5. Shiel RE, Pinilla M, McAllister H, et al. Assessment of the value of quantitative thyroid scintigraphy for determination of thyroid function in dogs. J Small Anim Pract 2012;53:278-285. 


Unknown said...

I had a full thyroid panel run on my dog (Vizsla) due to the fact that he recently started having seizures. His TgAA was positive/elevated (29) and the lab results stated he has autoimmune thyroiditis and recommends Soloxine and retesting in 8-12 weeks. The veterinarian who reluctantly ran the test for me, does not agree with the recommendation of medication and does not believe that my dog has a thyroid issue because T4 was normal. How should I proceed?

Dr. Mark E. Peterson said...

Was the free T4. T3 and TSH also normal? If so, I agree with your veterinarian. The presence of thyroid antibodies does not equate to hypothyroidism. Just means that we need to monitor thyroid function closely in the future.

Unknown said...

Yes to T4 and T3 being normal. TSH was not run. I will continue to monitor.

catarina said...

HI Dr. Mark.I have a persian cat that eat renal food for three years now,and today I made her blood analysis and the urea was 35, normal, and the creatinine 1.7,she has this value for the last 2 years...But phosphorous, that she never made before is too high is almost 12...What should I do? I wanted to know your opinion..Is this because of the kidneys? Or anything else? Should I try to giver her aluminium hidroxyde to low the levels?
Hope you can help me.

Dr. Mark E. Peterson said...

Why are you posting this question under dogs and hypothyroidism? Yes, hyperphosphatemia is likely the result of worsening kidney disease and phosphate binders can be helpful. Talk to your vet.