# What is your thyroglobulin level after I131 ?



## Want2FeelGood

For over a year after I131, my thyroglobulin has been 0.5 - 0.8. Seems disappointing. Should it actually go to zero with successful treatment ? Does a low level for months to years always mean residual PTC ?


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## joplin1975

Mine was 0.3 one year out and I was told that was "prefect."


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## Abcdefg

Mine is currently at least 350. My mind can't wrap around it Eek

I hope it is able to decrease to a lower level after treatment, but I imagine it'll be tested quite frequently.


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## Want2FeelGood

joplin1975 said:


> Mine was 0.3 one year out and I was told that was "prefect."


Doesn't thyroglobulin go to zero with successful treatment?


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## joplin1975

I was never under that impression...I was told some -- in fact many -- patients have very low levels of thryoglobulin after successful treatment. I had a RAIU, ultrasound, and thryoglobulin levels run and there is no evidence of disease.

http://www.cornellsurgery.org/pro/services/endocrine/thyroid-follow-up.html

Therefore, a serum thyroglobulin level above 5 ng/mL after rhTSH stimulation is highly sensitive in identifying patients with persistent disease. Furthermore, the clinical significance of minimally detectable thyroglobulin levels is unclear, especially if only detected after TSH stimulation.


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## joplin1975

Also:

The prevalence of postablation thyroid cancer recurrence is predicted by the rhTSH-Tg
response with an optimal Tg threshold of 2.5 ng/ml. Still, recurrent disease occurs in some patients with an initial rhTSH-Tg of 0.5 ng/ml or less.

http://jcem.endojournals.org/content/95/12/5241.full.pdf

I think the take home message is that Tg is a marker, but not a definitive tool for assessing recurrence.


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## joplin1975

One more:

Undetectable thyroglobulin levels while the patient is on thyroid hormone usually indicate that there is no evidence of residual or recurrent thyroid cancer. Similarly, a detectable but low (<1) thyroglobulin level that is stable over time usually indicates that there is no evidence of residual or recurrent thyroid cancer.

...

This study shows that only 4% of thyroid cancer patients with a thyroglobulin level <1 on thyroid hormone have a recurrence of their cancer 5 years after their initial treatment. A stimulated thyroglobulin test identified these patients with cancer recurrence. Thus, this study shows that performing a repeat stimulated thyroglobulin test is reasonable 5 years after initial treatment for thyroid cancer in patients with low but detectable thyroglobulin levels on thyroid hormone treatment. Further, this study suggests that no further stimulated thyroglobulin tests are necessary if the test is negative at 5 years.

http://www.thyroid.org/wp-content/uploads/publications/ctfp/volume5/issue8/ct_patients_v58_5_6.pdf


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## Want2FeelGood

What's strange is that the thyroglobulin peaks after they decide whether or not to treat with I131 by using the I123 scan. I had TG 0.6 baseline, then after two days of thyroxin, my TG was 0.4 and I123 scan negative so no I131 was given. But three days after the 123 scan my TSH was 20 and TG was 0.9 . That 0.9 doesn't look good. Is that bad ?

How many of you get your TG checked 4-5 days after thyrogen ? Has it been zero ? So does the 0.9 value mean next year I131 will be needed ?


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## joplin1975

Any reason they tested your tg four days out? I can't imagine any reason to do so.

But, no, I don't think it's bad. If you read the links, they said anything under one is a-ok. Combine that with good WBS scan results and, well, I think at this point you are borrowing trouble by worrying about this.


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## Want2FeelGood

joplin1975 said:


> Any reason they tested your tg four days out? I can't imagine any reason to do so.


Good question. Maybe the reason = that's when thyroglobulin peaks. When the thyroglobulin is measured at the time of I123 administration, or during the time of the I123 scan, that is not the peak of thyroglobulin.

Guess this peak value helps determine if I131 should be given in a year. Anyone know ?


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## joplin1975

Don't know...

This says it reaches maximum levels 72 hours after final injection: 
The maximum Thyrogen Tg value was obtained 72 hours after the final Thyrogen injection, and this value was used in the analysis (see DOSAGE AND ADMINISTRATION).

http://www.theodora.com/drugs/thyrogen_for_injection_genzyme.html

ETA: Did you have a neck ultrasound with your scan? You could ask about that and the ultra-sensitive Tg assay: http://www.ncbi.nlm.nih.gov/pubmed/21399390


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