Thyroid Issues After Total Thyroidectomy: Free T4 Levels and Heart Health

Q: Thyroid Issues After Total Thyroidectomy: Free T4 Levels and Heart Health

Dear Ms. <br>Liang：<br>1. <br>After undergoing a total thyroidectomy due to papillary thyroid carcinoma, secondary hypothyroidism often occurs, necessitating long-term thyroid hormone replacement therapy. <br>Levothyroxine (T4) is typically used for this treatment; due to its lon

Thyroid issues?

Hello, doctor! I have undergone a total thyroidectomy due to papillary thyroid carcinoma.
Currently, I am taking Eltroxin 0.1 mg, averaging 1.5 tablets per day.
During my follow-up visits, my doctor has mentioned that my reports are normal.
However, recently I have experienced episodes of my heart skipping beats, and upon visiting a cardiologist, I was informed that my free T4 level is elevated (1.9).
(The metabolic and cardiology departments are in different hospitals.) I would like to ask if the interpretation of free T4 levels is the same for patients who have had a total thyroidectomy compared to those who still have their thyroid gland.
Can an excessive dosage of Eltroxin lead to pulmonary hypertension? (As I have this condition.) Thank you, doctor!

Liangliang, 40~49 year old female. Ask Date: 2017/06/14

Dr. Xiao Yongxun reply Internal Medicine

Dear Ms.
Liang:
1.
After undergoing a total thyroidectomy due to papillary thyroid carcinoma, secondary hypothyroidism often occurs, necessitating long-term thyroid hormone replacement therapy.
Levothyroxine (T4) is typically used for this treatment; due to its long half-life, it is taken once daily, and it takes about 6 to 8 weeks of administration to reach a stable concentration in the body.
2.
As for its toxic reactions or side effects, they are generally directly related to the serum concentration of T4.
Possible symptoms may include nervousness, palpitations, tachycardia, heat intolerance, or weight loss.
3.
Pharmacologically, both T4 and T3 must first dissociate from thyroxine-binding globulin in the plasma before they can enter the cells; this entry can occur via passive diffusion or active transport.
4.
Inside the cells, T4 is converted to T3 through the action of deiodinase enzymes, and T3 subsequently enters the cell nucleus to bind with specific receptors.
The activation of these receptors promotes RNA formation and subsequent protein synthesis, which is the primary action of T4.
5.
Food, calcium-containing medications, and aluminum-containing antacids can reduce the absorption of T4; however, T3 is not affected.
The conversion of T4 to T3 is mediated by one of two specific deiodinase enzymes, depending on the tissue.
6.
The metabolism of thyroid hormones occurs through the cytochrome P450 system; drugs that induce P450 enzymes, such as phenytoin, rifampin, and phenobarbital, can accelerate the metabolism of thyroid hormones.
7.
The above descriptions explain that the levels of T4 or Free T4 can vary due to diet, medications, metabolism, or disease states.
Therefore, it is quite possible that both hospitals' test results are correct.
Although the reference values for Free T4 may vary slightly among different laboratories, the differences should not be significant.
8.
There are many causes of pulmonary hypertension, with common clinical causes including pulmonary embolism, chronic obstructive pulmonary disease, congenital heart disease or vascular lesions, and hyperthyroidism, among others.
I cannot determine the cause in your case; however, excess thyroid hormone can indeed exacerbate hyperthyroid symptoms, including the aforementioned nervousness, palpitations, tachycardia, heat intolerance, or weight loss.
9.
I recommend that you discuss this thoroughly with your endocrinologist before making any decisions.
In fact, after a total thyroidectomy, long-term follow-up is essential.
Once your condition is very stable, the intervals for follow-up can be considered for extension.

Reply Date: 2017/06/14

More Info

After a total thyroidectomy, especially due to conditions like papillary thyroid cancer, managing thyroid hormone levels becomes crucial for overall health. The medication you are taking, Eltroxin (levothyroxine), is a synthetic form of the thyroid hormone thyroxine (T4) and is essential for replacing the hormones that your body can no longer produce due to the removal of the thyroid gland.

Understanding Free T4 Levels
Free T4 is a measure of the unbound thyroxine in the bloodstream, which is the active form of the hormone that can enter cells and exert its effects. In patients who have undergone total thyroidectomy, the interpretation of Free T4 levels can differ from those who still have a functioning thyroid gland. For individuals without a thyroid, the goal is to maintain Free T4 levels within a specific range that mimics normal thyroid function. This range may be slightly higher than that of individuals with a functioning thyroid, as the body is adjusting to the absence of the gland.

In your case, a Free T4 level of 1.9 ng/dL is considered elevated, especially if the reference range for your lab is around 0.93-1.7 ng/dL. This elevation can lead to symptoms of hyperthyroidism, such as palpitations, anxiety, and even heart rhythm irregularities, which you have experienced. It is essential to communicate these symptoms to your healthcare provider, as they may indicate that your Eltroxin dosage needs adjustment.

Eltroxin Dosage and Side Effects
The dosage of Eltroxin you mentioned (0.1 mg, averaging 1.5 tablets daily) may be too high for your needs, especially if your Free T4 levels are elevated. Overmedication can lead to hyperthyroid symptoms and potentially serious complications, including heart issues. While pulmonary hypertension can have various causes, excessive thyroid hormone levels can exacerbate or contribute to cardiovascular problems. Therefore, it is crucial to monitor your thyroid hormone levels regularly and adjust your medication accordingly.

Monitoring and Adjustments
Since you are experiencing symptoms like heart palpitations, it is advisable to consult with both your endocrinologist and cardiologist. They can work together to determine the best course of action. Your endocrinologist may want to lower your Eltroxin dosage to bring your Free T4 levels back into the normal range. It is also important to monitor your TSH (Thyroid Stimulating Hormone) levels, as they can provide additional insight into your thyroid function and medication effectiveness.

Conclusion
In summary, after a total thyroidectomy, Free T4 levels are interpreted with the understanding that the patient is reliant on medication for hormone replacement. Elevated Free T4 levels can lead to significant health issues, including cardiovascular problems. It is essential to work closely with your healthcare providers to adjust your Eltroxin dosage and manage your symptoms effectively. Regular follow-ups and blood tests will help ensure that your thyroid hormone levels remain stable and within the desired range, promoting your overall health and well-being.

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