Thyroid Tests Can Be Wrong

Buzz`s case

Buzz is a happy little Yorkie who has been generally healthy, is slightly overweight, and has chronic knee (patella) problems that were addressed surgically several years ago. Early in September, Buzz became acutely ill with vomiting and was started on antibiotics. Blood taken when she was acutely ill showed no anemia and no elevated cholesterol. One of the five types of white blood cells was low (lymphopenia), which is common in stress. Neutrophils, the white blood cells that are elevated in acute infection were normal. Her T4 and free T4 were both low. (Normal T4 is 13-53 ; Buzz`s T4 was 11.6 Normal free T4 is 7.7-47.6 ; Buzz`s was 6.4.) The veterinarian commented on the blood test that Buzz was lethargic with vomiting, anorexia and fever (pyrexia). The pathologist who reviewed the blood test noted the low free T4 and diagnosed hypothyroidism. Buzz`s vet told the family that based on this single lab test taken when she was acutely ill, Buzz will need medication for life.

Is this hypothyroidism or euthyroid sick syndrome?. “Eu” thyroid means “good” thyroid.

It may be that Buzz has euthyroid sick syndrome and the diagnosis of hypothyroidism is premature. I recommend that the family wait 4-6 weeks, and when Buzz is healthy, she can receive a physical exam that includes reflexes. IF she is symptomatic for hypothyroidism, run a repeat T4. If the T4 is abnormal, add on a free T4 and TSH. In the meantime, it is not recommended to give thyroid meds to euthyroid sick dogs. Dogs with a sudden (acute) illness or with a chronic illness may have abnormally low thyroid tests without having an abnormal thyroid gland. These dogs have euthyroid sick syndrome

Let’s discuss euthyroid sick syndrome by answering 5 questions:

1. How does a dog with a normal thyroid look and function?
2. How does a dog with an abnormal thyroid (hypothyroidism) look and function?
3. How does the blood of a healthy dog look?
4. How does the blood of a hypothyroid dog look?
5. Is Buzz taking medication that affects thyroid function?

1.       How does a dog with a normal thyroid look and function?

Dogs with healthy thyroid glands have a normal amount of energy and appear healthy. Skin cells maintain a full, shiny coat. Gut cells maintain good digestion and regular stools. Nerve cells maintain normal reflexes, including patellar reflexes and proprioception. Bone marrow produces red blood cells so that haemoglobin and hematocrit are normal (no anemia). The brain is active and dogs want to play. The face is happy and relaxed. The weight is normal. The thyroid helps all this occur because it helps determine the rate that cells burn fuel (metabolic rate). Every cell in the body is influenced by the thyroid.

2.       How does a dog with an abnormal thyroid (hypothyroidism) look and function?

Hypothyroid dogs look sluggish. They have a sad, “hang dog” expression caused by fluid collection (myxedema). Hypothyroid dogs are often overweight with a thinning hair coat, especially noticeable over the flanks and the tail. They often have dry skin or dander, increased tendency toward skin infections, and hyperpigmentation. They are lethargic, don’t enjoy toys, aren’t eager for walks. Hypothyroid dogs may have slow, weak reflexes, poor proprioceptive placing.

3.       How does the blood of a healthy dog look?

Healthy dogs are not anemic and have normal red blood cells. They don’t have infections and have normal white blood cells. Healthy dogs have normal cholesterol levels. Thyroid tests are within normal limits, including T4, free T4, T3, TSH, and thyroid autoantibodies.

4.       How does the blood of a hypothyroid dog look?

Hypothyroid dogs usually have nonregenerative anemia and elevated cholesterol. Their white blood cells remain normal. T4 is usually low; free T4, low; TSH, normal or high; autoantibodies, elevated early in disease before the thyroid is obliterated.

5.      Is Buzz taking medications that affect thyroid function?

Buzz has knee problems and may take joint meds, but is not reported to be using any meds that affect the thyroid.

Medications that affect thyroid tests

Some meds affect thyroid tests and give the impression of hypothyroidism. Among the meds that cause an artificially low T4 are

·         Aspirin

·         Amitriptyline

·         Clomipramine (Clomicalm)

·         Phenobarb

·         Steroids, oral or in eye or topical medications

·         Sulfa

·         Zonisamide

Meds that don’t affect thyroid

·         Meloxicam (Metacam)

·         Carprofen (Rimadyl)

·         Glucosamine

 Thyroid Function During Critical Illness

Humans, like dogs, may develop thyroid disease, and research done on humans helps us understand what happens to dogs with thyroid disease.  The following abstract is from Thyroid Function During Critical Illness by Foteini, et al published in Hormones 2011 Apr-Jun;10(2):117-24.  This research shows why using blood test taken while Buzz was acutely ill should not be used to diagnose hypothyroidism.

The metabolic support of the critically ill patient is a relatively new target of active research and little is as yet known about the effects of critical illness on metabolism. The nonthyroidal illness syndrome, also known as the low T3 syndrome or euthyroid sick syndrome, describes a condition characterized by abnormal thyroid function tests encountered in patients with acute or chronic systemic illnesses. The laboratory parameters of this syndrome include low serum levels of triiodothyronine (T3) and high levels of reverse T3, with normal or low levels of thyroxine (T4) and normal or low levels of thyroid-stimulating hormone (TSH). This condition may affect 60 to 70% of critically ill patients. The changes in serum thyroid hormone levels in the critically ill patient seem to result from alterations in the peripheral metabolism of the thyroid hormones, in TSH regulation, in the binding of thyroid hormone to transport-protein and in receptor binding and intracellular uptake. Medications also have a very important role in these alterations. Hormonal changes can be seen within the first hours of critical illness and, interestingly, these changes correlate with final outcome. Data on the beneficial effect of thyroid hormone treatment on outcome in critically ill patients are so far controversial. Thyroid function generally returns to normal as the acute illness resolves.

 

Based on research, history, and the family’s observation of Buzz, I think Buzz has euthyroid sick syndrome. The family should consult another veterinarian who looks at the whole picture. If Buzz appears symptomatic for thyroid disease in a month, her blood tests can be repeated. Let's get the diagnosis correct before telling this family their pet has  a disease that requires lifelong treatment.

 

 

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