From the FDA Drug Label
The general aim of therapy is to normalize the serum TSH level TSH may not normalize in some patients due to in utero hypothyroidism causing a resetting of pituitary-thyroid feedback. Failure of the serum T4 to increase into the upper half of the normal range within 2 weeks of initiation of levothyroxine sodium therapy and/or of the serum TSH to decrease below 20 IU per litre within 4 weeks may indicate the patient is not receiving adequate therapy
A TSH of 12.8 while on Synthroid for a total thyroidectomy is atypical if the goal of therapy is to normalize the serum TSH level.
- Key points:
- The general aim of therapy is to normalize the serum TSH level.
- A TSH of 12.8 is above the normal range, indicating that the patient may not be receiving adequate therapy.
- Even if T4 and T3 are normal, a high TSH level may indicate that the patient is not receiving adequate therapy or that there are other factors at play, such as poor compliance or abnormal values.
- The FDA label does not provide a specific definition of a "normal" TSH range, but it does indicate that the goal of therapy is to normalize the serum TSH level 1 1.
From the Research
A TSH of 12.8 while on Synthroid (levothyroxine) after a total thyroidectomy is definitely atypical and indicates inadequate thyroid hormone replacement, even if T4 and T3 levels appear normal. This situation requires a dosage adjustment of your Synthroid. After a total thyroidectomy, the goal is typically to maintain TSH in a lower range (often between 0.5-2.0 mIU/L) to ensure proper replacement of thyroid hormone, as suggested by the study published in the Journal of Clinical Medicine in 2022 2. The discrepancy between your elevated TSH and normal T4/T3 levels could indicate several issues:
- Your body may be trying to compensate for insufficient thyroid hormone at the tissue level
- There might be problems with medication absorption
- You could have developed resistance to the current dosage. You should contact your endocrinologist promptly to discuss increasing your Synthroid dose. Do not adjust your medication without medical supervision. Your doctor will likely increase your dose gradually and recheck your levels in 6-8 weeks. Factors that can affect levothyroxine absorption include taking it with food, calcium supplements, iron supplements, or certain medications, so take it on an empty stomach, 30-60 minutes before breakfast or other medications for optimal absorption, as supported by the study published in the European Journal of Endocrinology in 2012 3. Additionally, a study published in the Journal of Surgical Research in 2019 4 developed a decision tree to estimate levothyroxine dose adjustments, which could be useful in your case. It is essential to follow your doctor's instructions and attend regular check-ups to ensure your thyroid hormone levels are within the target range, as emphasized by the study published in Thyroid in 2014 5 and Clinical Endocrinology in 2011 6.