
What Causes Abnormal TSH Levels Despite Taking Synthroid?

Thyroid
Detailed Answer:
I follow what you are saying.
Thyroid management can be complex and is best handled by a trained endocrinologist in person.
When I see someone in my practice with similar laboratory results, I order the following tests in addition to a thorough physical examination:
CBC
CMP
TSH
Free T4
Total T3
T3 resin uptake
anti TPO antibodies
anti Thyroglobulin antibodies
Prolactin
FSH
LH
8 am serum cortisol
It is possible that on that basis of findings on physical examination I may order fewer tests or more tests.
There is an uncommon condition called Central or Secondary Hypothyroidism that needs to be ruled out.
Moreover, there are certain types of medications that tend to lower the TSH such as steroids and opioids.


Follow up
Detailed Answer:
You are probably referring to Hashimoto's disease.
Yes it is one of the most commonest causes for a permanently under-active thyroid, necessitating lifelong treatment with levo thyroxine (of which Synthroid is one brand name medication).
The two antibody tests mentioned above are helpful is diagnosing this condition. Other indications as to whether it is present come from physical examination.

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