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Off-the-chart TSH and heterophilic antibodies
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A 40-year-old woman, several years post-thyroidectomy for management of thyroid cancer with concomitant parathyroidectomy, had been doing very well until about 2 years before I saw her as a patient.
A few days before her clinic visit, her primary care provider sent me the most comprehensive clinical encounter report that I have seen in a long time, and several items caught my attention immediately.
As you can see from the table below, the patient had struggled for a few years to maintain a euthyroid state on a 200-mcg dose of thyroxine and a 25-mcg dose of T3. She reported that she was having trouble tolerating some oral medications, particularly her thyroid medicines, and transdermal thyroid hormone was being considered.
Source: Michael Kleerekoper, MD, MACE
I have done an extensive search on PubMed and found no information about transdermal thyroxine in humans. When I performed a Google search, I found a plethora of websites, but only one of the first 50 that I looked at had anything to say about transdermal thyroxine. There was, however, plenty of information about transdermal estrogen and transdermal methimazole, but the latter was for dogs, not humans.
The day after receiving the clinical encounter note from the patient’s PCP, I received the lab data and could not believe the TSH result.
Clinically, my patient was not feeling up to par, but there were no significant findings on examination that were consistent with under- or overtreated thyroid or parathyroid disease.
She was very patient and pleasant as the resident and I reviewed all the data that we had from the history, physical, PCP encounter note and off-the-wall TSH.
I was very confident that the reported TSH of 427 was a lab error and was very surprised to see that a second lab came up with nearly the same value. I contacted the lab to express my concern and was floored by the pathologist’s response: “Sometimes we see high values.”
That was clearly an inadequate response, and I am very confident that the reported, exceptionally high TSH values were related to heterophilic antibodies. That said, I have had a tough time finding appropriate literature to explain this phenomenon. The best I can find is a recommendation to measure TSH values by several of the available assays.
Help from readers of this blog would be appreciated.