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When Tg levels are so low or even undetectable that everything is fine?
Thyroglobulin (Tg), as one of the most commonly used indicators to monitor the recurrence and metastasis of differentiated nail cancer, can be said to be loved and hated!
Serum thyroglobulin levels are a sensitive indicator
of the presence of thyroid tissue in the body.
Physiologically, TSH is the most important regulator of thyroglobulin production and release
.
The normal value of Tg in normal people is 3-40μg/L
.
One
So, is it only normal thyroid tissue that synthesizes Tg?
Of course not!
We all know that normal thyroid tissue and differentiated thyroid cancer cells are the only source of Tg in peripheral blood, and the detection of Tg level is a sensitive and specific method in the follow-up of DTC patients, which is also an important theoretical basis for Tg to detect the recurrence and metastasis of differentiated thyroid cancer: Tg is a specific indicator of differentiated nail cancer in patients with differentiated nail cancer after total thyroidectomy and iodine-131 removal of residual thyroid tissue.
Tg should disappear completely or be at very low levels; If the reappearance or elevation of Tg is a sign of uncured, recurred, or metastatic differentiated nail cancer, then the patient is likely to have thyroid cancer recurrence or persistent cancer lesions
.
Two
When Tg levels are so low or even undetectable that everything is fine?
Of course not!
There are many factors that affect Tg:
1.
Residual thyroid tissue
.
When there is more residual nails, there is no doubt that Tg will increase, and conversely, Tg will decrease
.
This is why TG cannot be used as the only test indicator for patients who have only undergone subtotal thyroidectomy
.
In fact, residual nails do not have much effect
on fluctuations in Tg concentration.
2.
Serum TSH index
.
TSH is the most important regulator of thyroglobulin production and release, TSH can promote tumor cells to produce Tg, Tg at this time is also called stimulant Tg; When TSH is inhibited, tumor cells produce Tg and also downregulate, and Tg at this time is called inhibitory Tg
.
This is why thyroid hormones need to stop for a while before doing iodine-131, and the elevated TSH makes the sodium iodine co-transporter (NIS) on the capsule of differentiated thyroid cancer cells fully expressed, and the uptake of iodine-131 is enhanced
.
Generally, when TSH > 30Mμ/L, it can significantly increase the uptake
of iodine-131 by cancer cells.
3.
Thyroglobulin antibody (TgAb).
When TgAb is elevated, the clinical value of Tg is greatly affected, and in most cases Tg levels are very low, when the reference value of Tg is low
.
However, studies have shown that in the follow-up of patients with A cancer, the presence of circulating TgAb may be associated with
recurrence after the lesion is still present.
However, some studies have shown that the reduction or disappearance of TgAb after treatment is an important favorable prognostic factor; After treatment for A cancer, even if Tg is negative, the persistence of Tgab, especially high levels of Tgab, may indicate the presence of recurrent or metastatic lesions; When the blood Tgab level after surgery for thyroid cancer > 1000 IU/L, it should be considered in follow-up; There is separation between Tgab, Tg and iodine-131 concentration, so the comprehensive application of the three can improve the detection rate of DTC metastasis or recurrence, which is helpful for the detection and treatment
of A cancer after surgery.
4.
Size and degree of differentiation of
lesions.
In general, the lesion is small and limited, the amount of Tg secreted is small, and the amount of Tg secreted will increase
if the lesion is large or distant metastases.
Whether the degree of differentiation of the lesion correlates with Tg levels has not been definitively studied
.
Therefore, the low level of Tg can not completely exclude the possibility of recurrence and metastasis in the body, and it is necessary to consider the above factors comprehensively, but also combine thyroid and cervical lymph node ultrasound, CT, PET/CT, MR and other examination results
if necessary.
Three
TG levels are very low, is iodine 131 treatment necessary?
Although the application of Tg-differentiated nail cancer is important, whether differentiated nail cancer needs to do iodine 131 is not just a reference to Tg
.
It is also necessary to divide patients after surgery for thyroid cancer into low-risk, intermediate-risk, and high-risk recurrence risk
according to clinicopathological characteristics.
Therefore, whether to be treated with iodine 131 after thyroid cancer surgery, Tg is not the only basis, but also needs to look at the clinicopathological features
of the patient.
When at high risk of recurrence, iodine-131 therapy must be given as soon as possible, and iodine-131 therapy is recommended in most cases when at intermediate risk of recurrence
.
Where to see more endocrinology clinical knowledge?
Come to the "doctor's station" and take a look 👇
SourceThyroid Doctor
Responsible editorTangerine
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