Early stimulated thyroglobulin for response prediction after recombinant human thyrotropin-aided radioiodine therapy
Early stimulated thyroglobulin for response prediction after recombinant human thyrotropin-aided radioiodine therapy
Hee Jeong Park 0 1 2
Jung-Joon Min 0 1 2
Hee-Seung Bom 0 1 2
Jahae Kim 0 1 2
Ho-Chun Song 0 1 2
Seong Young Kwon 0 1 2
0 Department of Nuclear Medicine, Chonnam National University Hospital , 42 Jebong-ro, Donggu, Gwangju 61469 , South Korea
1 Department of Nuclear Medicine, Chonnam National University Hwasun Hospital , 322 Seoyang-ro, Hwasun-eup, Hwasun-Gun, Jeonnam 58128 , South Korea
2 & Seong Young Kwon
Objective Measurement of recombinant human thyrotropin (rhTSH)-stimulated thyroglobulin (Tg) is generally recommended 72 h after the second rhTSH injection. However, due to the acute effect of I-131 on thyrocytes, Tg measured after radioiodine therapy (RIT) would not accurately reflect the thyroid tissue burden. We aimed to determine predictive values of serum Tg level measured just before rhTSH-aided RIT and to compare the results obtained just after RIT in patients with differentiated thyroid carcinoma (DTC). Methods We evaluated 150 patients with DTC who underwent rhTSH-aided RIT (2.96-6.66 GBq) after total thyroidectomy between 2009 and 2014. Serum Tg level was measured 24 h (early Tg) and 72 (or 96) h (delayed Tg) after the second rhTSH injection. An excellent response was defined based on the latest American Thyroid Association Guidelines. Univariate and multivariate analyses were performed for early Tg, delayed Tg, and other clinical variables. Results In the multivariate analysis, tumor size [odds ratio (OR) 1.716; 95% confidence interval (CI) 1.019-2.882; p = 0.042] and early Tg level (OR 2.012; 95% CI 1.384-2.925, p \ 0.001) independently predicted excellent responses. The cutoff for the best early Tg level to predict a non-excellent response was 2.0 ng/mL. Delayed Tg was not a significant predictor (OR 0.992; 95% CI 0.969-1.015; p = 0.492). Conclusions Early stimulated Tg significantly predicted therapeutic response after rhTSH-aided RIT in patients with DTC. Therefore, serum Tg should be measured before RIT to predict therapeutic responses.
Differentiated thyroid carcinoma; Radioiodine therapy; Recombinant human thyrotropin; Thyroglobulin; Therapeutic response
Total thyroidectomy followed by radioiodine therapy (RIT)
is the treatment of choice for differentiated thyroid
carcinoma (DTC) [
]. Although DTC shows a relatively good
response to RIT, unsuccessful ablation is reported in about
6–30% of patients [
], so additional treatments, such as
surgical procedures or repeated RIT, and life-long
followup are required. Serum thyroglobulin (Tg) levels measured
during hypothyroidism, just before RIT, have good
prognostic values for predicting successful ablation [
Recombinant human thyrotropin (rhTSH) represents a
safe and effective means of increasing serum TSH in
preparation for RIT, avoiding signs and symptoms of
hypothyroidism associated with thyroid hormone
withdrawal (THW) [
]. I-131 is usually administered on
the day after the 2nd injection of rhTSH according to the
conventional schedule [
]. On the other hand, serum Tg
should be measured 72 h after final injection of rhTSH,
because this day corresponds to the peak serum Tg levels
]. However, due to the radioiodine-induced damage
to normal thyroid cells and release of stored Tg in thyroid
follicles, the Tg level measured after RIT would not be
reliably predictive [
The present study was undertaken to determine the value
of Tg measured before and after RIT that predicts a
therapeutic response in DTC patients with rhTSH-aided RIT.
determined by IRMA (TSH-CTK-3, DiaSorin, Saluggia,
Italy) with an AS and FS of 0.04 and 0.07 mU/L,
respectively. The cut-off point for TSH, above which
corresponding stimulated Tg levels were acceptable, was
Materials and methods
Between August 2009 and May 2014, 430 DTC patients,
who underwent total or near-total thyroidectomy followed
by rhTSH-aided RIT in our institution, were initially
analyzed. Among these patients, patients with high levels of
serum anti-Tg autoantibodies (TgAbs) more than 100 IU/
mL (n = 37), repeated RIT (n = 27), missing Tg
measurements (n = 109), distant metastases (n = 8), and
insufficient follow-up (n = 99) were excluded. Finally,
150 patients were enrolled in this study. This retrospective
study was performed in accordance with the ethical
standards laid down in the 1964 Declaration of Helsinki and its
later amendments, and ethical approval was obtained from
the local ethics committee (CNUHH-2016-069). For this
type of study, informed consent was waived.
Patients were referred for RIT 0–27 months (mean
4.0 months) after surgery. All patients had received 2
consecutive daily doses of 0.9 mg rhTSH (Thyrogen,
Genzyme Transgenics Corp., Cambridge, USA)
administered by the intramuscular route prior to RIT. According to
the instructions regarding limiting exposure to
environmental iodine, patients consumed a low-iodine diet for
2 weeks prior to RIT. Twenty-four hours after the 2nd
injection of rhTSH, a therapeutic dose of I-131
(2.96–6.66 GBq) was administered. An I-131 whole body
scan was performed 7–8 days after oral ingestion of I-131.
Tg and TSH measurement
For serum Tg measurements, blood samples were collected
two times: before RIT (24 h after the 2nd rhTSH injection)
(early Tg) and after RIT (72 or 96 h after the 2nd rhTSH
injection) (delayed Tg). Serum Tg was measured by an
immunoradiometric assay (IRMA) (RIA Tg-plus,
BRAHMS GmbH, Hennigsdorf, Germany) with an
analytical sensitivity (AS) and functional sensitivity (FS) of
0.08 and 0.2 ng/mL, respectively. Serum TgAbs was
measured by a radioimmunoassay method (RIA anti-Tgn,
BRAHMS GmbH, Hennigsdorf, Germany) with an AS of
5.5 U/mL and FS of \20 U/mL. Serum TSH levels were
The first post-ablation follow-up examination was
performed 6–12 months (mean 9.0 months) after RIT. The
follow-up protocol included neck ultrasound (US) and
serum Tg measurement. Suppressed Tg was measured in
60 patients, and the remainder of the patients (n = 90)
underwent diagnostic I-123 whole body scan (DxWBS)
with stimulated Tg aided by rhTSH or endogenous TSH.
Definitions of therapeutic responses followed the 2015
American Thyroid Association Guidelines [
excellent response—negative imaging and either suppressed Tg
\0.2 ng/mL or TSH-stimulated Tg \1 ng/mL; (2)
biochemical incomplete response—negative imaging and
suppressed Tg C1 ng/mL or stimulated Tg C10 ng/mL; (3)
structural incomplete response—structural or functional
evidence of disease with any Tg level with or without
TgAbs; (4) indeterminate response—nonspecific findings
on imaging studies or suppressed Tg detectable but \1 ng/
mL or stimulated Tg detectable but \10 ng/mL. We
classified patients into 2 groups: the excellent response group
and the non-excellent response group (which included
those showing a biochemical incomplete response,
structural incomplete response, and indeterminate response).
Using a logistic regression analysis, clinicopathologic
variables were tested for their association with an excellent
response using a univariate analysis: early Tg, delayed Tg,
other clinical (age at diagnosis, sex, I-131 dose), and
pathologic markers [American Joint Cancer Committee
(AJCC)/International Union Against Cancer (UICC) TNM
staging (7th edition), presence of extra-thyroid extension,
tumor size, multicentricity, and bilaterality]. Variables with
p value B0.20 were further analyzed by a multivariate
logistic regression analysis using the stepwise backward
]. A p value \0.05 was considered
statistically significant. A receiver-operating characteristic (ROC)
curve analysis was used to define the best cut-off value for
serum Tg at ablation. For the established cut-off value, we
calculated the sensitivity, specificity, positive predictive
value (PPV), negative predictive value (NPV), and area
under the curve (AUC). Statistical analysis was performed
using SPSS version 21.0 for Windows (IBM Corp.,
Patients’ characteristics are summarized in Table 1. The
study population comprised 114 women (76.0%) and 36
men (24.0%), aged 20–79 years (mean 48.8) at the time of
surgery. The histological DTC subtype was papillary in
148 cases (98.7%) and follicular in 2 cases (1.3%). At the
time of RIT, early Tg ranged from 0.1 to 117.9 ng/mL
(mean 3.2) and delayed Tg ranged from 0.1 to 198.7 ng/mL
At the follow-up examination, an excellent response was
observed in 85 (56.7%) patients. In the 65 (43.3%) patients
with non-excellent responses, 10 (6.7%) patients had a
biochemical incomplete response, 10 (6.7%) had a
structural incomplete response, and 45 (30.0%) had an
Variables significantly associated with an excellent
response in the univariate analysis are reported in Table 2.
Older age (p = 0.041), smaller tumors (p = 0.009), and
low level of early Tg (p \ 0.001) significantly predicted an
excellent response. In the multivariate logistic regression
analysis, early Tg [odds ratio (OR) 2.012; 95% confidence
interval (CI) 1.384–2.925; p \ 0.001] and tumor size (OR
1.714; 95% CI 1.019–2.882; p = 0.042) significantly
predicted an excellent response (Table 3). However, delayed
Tg did not show statistical significance for response
prediction after RIT (OR 0.992; 95% CI 0.969–1.015;
p = 0.492).
An ROC curve analysis showed that the optimal cut-off
value for early Tg was 2.0 ng/mL; it had a sensitivity of
46.2%, specificity of 95.3%, PPV of 88.2%, and NPV of
69.8% for predicting a non-excellent response (AUC 0.704;
p \ 0.001) (Fig. 1). In 116 patients with an early Tg level
B2.0 ng/mL, an excellent response was observed in 81
patients (69.8%), whereas only 4/34 (11.8%) patients with
early Tg levels [2.0 ng/mL showed an excellent response
In patients with DTC, the stimulated Tg level measured
just before RIT proved to be a biochemical tumor marker
that could predict persistent or recurrent disease after THW
]. In a recent meta-analysis involving 3947 patients
across a broad spectrum of disease, it was demonstrated
that the pre-ablation Tg level could be a useful negative
predictor of persistent or recurrent DTC. The overall NPV
was 94% when the pre-ablation Tg level was \10 ng/mL
. In addition, the stimulated Tg measured after THW
could be used to predict the volume of the thyroid remnants
or the residual tumor burden [
]. However, there is no
consensus available with respect to the clinical
implications or testing protocol for stimulated Tg at rhTSH-aided
RIT, although rhTSH is now widely used as a method for
From the previous studies, serum Tg should be
measured in the 3 days after the 2nd injection of rhTSH
]. In 1998, Genzyme showed the serial Tg data that
resulted in FDA approval. In that study protocol, 24 h after
the 2nd rhTSH injection, 148 MBq radioiodine were
administered orally and Tg levels were measured on days
1, 2, 3, and 7. They found that maximum serum Tg levels
were observed on day 3 in most patients. However, the
administered dose of radioiodine was not a therapeutic
dose that could cause acute thyroid injury . This timing
of Tg measurement has raised concerns about its reliability
as a tumor marker, because acute thyroid injuries would
contribute to Tg production. Taieb et al. [
sequential elevation of median serum Tg levels during the
48 h after I-131 administration (3.7 GBq) in DTC patients
with hypothyroidism. Tg levels increased due to an acute
effect of I-131 on Tg release. Furthermore, the Tg
increments at 48 h were not correlated with Tg levels
measured before I-131 administration.
There have been inconsistent studies to show the
prognostic value of early Tg and delayed Tg in DTC patients
prepared with rhTSH. Ciappuccini et al. [
] showed a
significant correlation between the rhTSH-stimulated Tg
levels measured immediately before RIT and persistent/
recurrent disease (PRD), defined as evidence of tumor
burden confirmed by histology or radiological modalities
on follow-up. The early Tg levels were significantly lower
in nonstructural (microscopic) than in structural
(macroscopic) residual disease. The reported Tg cut-off value for
predicting PRD was 2.8 ng/mL, closed to the threshold
defined in our study, with a sensitivity of 86%, specificity
of 64%, PPV of 24%, and NPV of 97%. On the other hand,
Melo et al. [
] demonstrated that rhTSH-stimulated Tg
measured 3 days after RIT had a predictive value for
disease persistence or recurrence 1 year later in 131
consecutive patients. From this study, Tg levels ranged from 0 to
1927 ng/mL and were significantly lower in the
diseasefree group (17.9 ± 49.1 vs 136.3 ± 341.0 ng/mL,
p \ 0.001), with an optimal Tg cut-off level of 7.2 ng/mL.
However, there was no previous report to compare the
prognostic value of early Tg and delayed Tg.
Our study showed that rhTSH-stimulated Tg level just
before RIT (early Tg) was an independent predictor of
excellent response on follow-up, whereas there was no
significant difference in Tg levels after RIT (delayed Tg)
between the excellent and non-excellent response groups
(5.3 ± 16.2 vs 14.9 ± 36.0, p = 0.074). Several
explanations could be possible. Compared to the study by Melo
et al., the proportion of patients with structural incomplete
responses among the non-excellent responders were very
low in our study (80.0 vs 15.4%). The Tg levels could also
reflect the proportion of structural incomplete responses in
a group of patients with non-excellent responses between
the two studies. Therefore, the Tg level after RIT (delayed
Tg) might not have a predictive value for a group of
patients with a low proportion of structural incomplete
responses, where acute injury effects of I-131 on Tg release
could affect the total level of Tg to evaluate remnant tissue
Giovanella et al. [
] suggested that even Tg measured
before TSH stimulation can reflect expression of thyroid
remnants by showing a significant relationship between
neck radioiodine uptake measured just before ablation and
Tg level measured before rhTSH stimulation and under T4
treatment. Our study showed that Tg cutoff at 2.0 ng/mL
provided high specificity (95.3%) and PPV (88.2%) for
predicting a non-excellent response, which could be very
helpful to decide follow-up strategy based on early Tg.
However, the early Tg still has several limitations as
predictive factor due to the short TSH stimulation time. In our
study, Tg cutoff at 2.0 ng/mL provided insufficient
sensitivity (46.2%) and NPV (69.8%). Tg cut-off value under
short TSH stimulation could affect diagnostic accuracy.
Our results also indicated that 30.2% of patients with Tg
levels B2.0 ng/mL could not achieve an excellent
response. Most of them belong to an indeterminate
response group (Table 4), which of 13–20% are
reclassified as having PRD over approximately 10 years of
]. Further investigations are necessary to overcome
the physiologic drawbacks of early Tg as a reliable
response, n (%)
response, n (%)
There are several limitations in our study. First, this
study was retrospective, so a selection bias was inevitable.
Especially, our protocol for I-131 dose selection has
changed over the years based on recent studies and
guidelines, which the choice of administered dose was
heterogeneous, although there was no significant difference
in therapeutic response among I-131 dose like previous
studies (Table 2) [
5, 6, 19
]. Second, delayed Tg was
measured 96 h after the 2nd injection of rhTSH in some
patients due to their admission schedules. However,
between the two patient groups undergoing Tg testing in 72
or 96 h, there was no significant difference in the delayed
Tg (9.8 ± 29.7 vs 8.8 ± 21.0 ng/mL, p = 0.832) and
delayed TSH (34.1 ± 27.1 vs 28.0 ± 28.1 mU/L,
p = 0.202) levels. Third, although assessment of
therapeutic responses was based on the latest ATA
guidelines, follow-up protocols were not consistent for all
patients. Some patients underwent DxWBS with
stimulated Tg, and some patients underwent neck US with
suppressed Tg. Further large-scale prospective studies are
required to better determine the significance of early Tg.
In conclusion, the early stimulated serum Tg just before
rhTSH-aided RIT significantly predicted therapeutic
responses after RIT in patients with DTC. Therefore,
physicians should consider measuring the serum Tg level
before RIT to predict the therapeutic response, although the
early Tg does not precisely reflect the remnant thyroid
tissue burden in DTC patients prepared with rhTSH.
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