Endokrynologia Pediatryczna Pediatric Endocrinology

Vol. 6/2007 Nr 3(20)
Endokrynologia Pediatryczna
Pediatric Endocrinology
Reliability of 4-day Variant of Insulin-like Growth Factor- I Generation Test
in Children with a Short Stature and Normal Growth Hormone Secretion in
Stimulating Tests
Ocena wiarygodności 4-dniowego wariantu testu generacji
insulinopodobnego czynnika wzrostowego-I u dzieci niskorosłych z
prawidłowym wydzielaniem hormonu wzrostu w testach stymulacyjnych
Joanna Smyczyńska, Maciej Hilczer, Renata Stawerska, Andrzej Lewiński
Department of Endocrinology and Metabolic Diseases, Medical University of Lodz, Polish Mother’s Memorial Hospital – Research Institute, Lodz, Poland
Klinika Endokrynologii i Chorób Metabolicznych Uniwersytetu Medycznego w Łodzi, Instytut Centrum Zdrowia Matki Polki w Łodzi
Adres do korespondencji:
prof. Andrzej Lewiński, Klinika Endokrynologii i Chorób Metabolicznych Uniwersytetu Medycznego w Łodzi, Instytut Centrum
Zdrowia Matki Polki, 93-338 Łódź, ul. Rzgowska 281/289, tel. 042 271 17 15, fax 042 271 13 43,
e-mail: [email protected]
Key words: insulin-like growth factor-I (IGF-I), growth hormone, IGF-I generation test, short statureIntroduction
Słowa kluczowe: insulinopodobny czynnik wzrostowy-I (IGF-I), hormon wzrostu, test generacji IGF-I, niedobór wzrostu
ABSTRACT/
ABSTRACT/STRESZCZENIE
Background. Insulin-like growth factor-I (IGF-I) is the main growth hormone (GH)-dependent mediator of GH
activity. In the patients with a short stature and excluded GH deficiency, IGF-I generation test should be performed.
However, there is no uniform standard of both the test protocol and the interpretation of results. The aim of the study
was to determine the possibly short time period of recombined human GH (rhGH) administration that allows to obtain
reliable test results. Material and methods. The analysis comprised the results of IGF-I generation test, performed
in 40 children with short stature, normal GH secretion and decreased IGF-I concentration. Blood samples for IGF-I
assessment were collected before and after 1, 4 and 7 days of rhGH administration in daily dose 0.1 IU/kg (samples
0, 1, 4 and 7). Results. Significant increase of IGF-I concentration was found in sample 1 vs. 0 and in sample 4 vs.
1, while the difference between samples 4 and 7 was insignificant. Strong correlations were observed between IGF-I
concentration in samples 4 and 7, as well as in samples 0 and 1 (r=0.86 and r=0.85, respectively; p<0.05). Conclusion.
4-day variant of IGF-I generation test seems to be optimal to assess IGF-I response to rhGH administration.
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Praca oryginalna
Endokrynol. Ped., 6/2007;3(20):27-33
Wstęp. Insulinopodobny czynnik wzrostowy I (IGF-I) jest najważniejszym obwodowym mediatorem działania hormonu wzrostu (GH). Test generacji IGF-I powinien być wykonywany u pacjentów z niedoborem wzrostu, u których
wykluczono niedobór GH. Dotychczas nie opracowano ani jednolitego standardu wykonywania testu, ani też obowiązujących zasad interpretacji jego wyników. Celem pracy było ustalenie możliwie najkrótszego okresu stosowania
preparatu ludzkiego rekombinowanego GH (rhGH), pozwalającego na uzyskanie wiarygodnych wyników testu. Materiał i metody. Analizą objęto wyniki testu generacji IGF-I, wykonanego u 40 dzieci z niedoborem wzrostu, z prawidłowym wydzielaniem GH i obniżonym stężeniem IGF-I. Próbki krwi na oznaczenie stężenia IGF-I pobrano przed
oraz po 1, 4 i 7 dniach podawania preparatu rhGH w dawce 0,1 IU/kg m.c./dzień (punkt 0, 1, 4 i 7). Wyniki. Stwierdzono znamienny wzrost stężenia IGF-I w punkcie 1 względem 0 i w punkcie 4 względem 1, podczas gdy różnica pomiędzy punktami 4 i 7 okazała się nieznamienna. Wykazano istnienie silnych korelacji pomiędzy stężeniami IGF-I w
punktach 4 i 7 oraz w punktach 0 i 1 (r=0,86 i r=0,85, odpowiednio, p<0,05). Wniosek. 4-dniowy wariant testu generacji IGF-I wydaje się optymalny dla oceny wpływu zastosowania preparatu rhGH na wydzielanie IGF-I.
Endokrynol. Ped., 6/2007;3(20):27-33
Background
Growth hormone (GH) is the main hormonal factor necessary for normal linear growing. Standard
procedures in diagnosing GH deficiency (GHD) are
GH provocative tests with different pharmacological stimuli. It is well known that disorders of spontaneous GH secretion (so-called neurosecretory
dysfunction – NSD), as well as decreased GH bioactivity may exist despite normal results of provocative tests. In both of the above situations, the therapy with recombined human GH (rhGH) is potentially effective. Thus, further diagnostic procedures
are necessary for proper identification of those patients, who may benefit during rhGH therapy.
Growth hormone activity is mediated by insulin-like growth factors (IGFs), particularly the most
important of them – IGF-I (previously known as somatomedin C). The decreased IGF-I secretion in the
patients with normal GH peak in stimulating tests
may be observed not only in the patients with decreased GH sensitivity but also in those with either
NSD or the decreased GH bioactivity [1]. In every
case, other disorders that may disturb IGF-I synthesis in terms of normal GH secretion (such as: hypothyrosis, malnutrition, malabsorption syndrome, liver diseases) should be excluded.
Diagnostic algorithm in children with short stature but excluded classic form of GH deficiency
provides IGF-I generation test, i.e. an assessment of
IGF-I secretion before and during short-term application of rhGH specimen. An increase of IGF-I concentration supports the usefulness of rhGH therapy
in such patients, while the lack of IGF-I increase indicates GH insensitivity and speaks against rhGH
application. In Poland, IGF-I generation test has
been included in diagnostic algorithm in children
28
qualified to rhGH therapy [2] but not as an obligatory procedure in any clinical situation.
Until now, there is neither the standard of test
protocol applied nor the uniform interpretation of
results in such a test. In previous studies, different
periods of rhGH application (most frequently either
7 or 4 days), different daily doses of rhGH (from
0.075 IU/kg to 0.2 IU/kg), as well as different principles of interpretation of test were applied (IGF-I
increase assessed as sufficient ranged from 15 ng/
mL to over 100 ng/mL) [3, 4, 5, 6, 7, 8]. The variety of test variants speaks for the necessity of introduction of the uniformed standard of IGF-I generation test at least for children qualified to rhGH therapy in Poland.
The aim of the study
The aim of the study was to compare IGF-I serum concentration before and after 1, 4 and 7 doses of rhGH in order to find a possibly short but still
reliable variant of the test. The applied rhGH dose
was similar to those administered routinely in GH
deficiency in children, thus enabling to predict the
possible rhGH therapy effect on IGF-I secretion.
Material and methods
The analysis comprised the results of IGF-I generation test performed in 40 children (33 boys, 7
girls), age 12.6±2.3 years (mean±SD), with a short
stature, slow height velocity and the decreased IGFI serum concentration despite normal GH secretion
in 2 routinely performed stimulating tests. A short
stature was defined as patient’s height below 3rd
centile for age and sex according to current reference values for Polish children [9]. Height velocity
was assessed with respect to appropriate normative
Smyczyńska J. i inni – Reliability of 4-day Variant of Insulin-like Growth Factor-I Generation Test...
data according to Romer et al. [2]. Growth hormone secretion was regarded as normal when GH peak
in at least 1 of the stimulating tests was above 10.0
ng/mL. It should be mentioned that the above interpretation, qualifying the patients with probable or
even confirmed NSD as presenting normal GH secretion, was assumed only for the study purpose. In
all the children, any chronic diseases that may disturb IGF-I synthesis, including malabsorption syndrome, undernutrition, liver diseases, were excluded; all the girls had normal female karyotype.
Blood samples for IGF-I concentration measurements were collected in morning hours before first
rhGH administration (sample 0) and after 1, 4 and
7 rhGH injections (samples 1, 4 and 7, respectively). The injections of rhGH in a daily dose 0.1 IU/kg
(0.033 mg/kg) were applied every day at 8 p.m. for
7 days. Serum IGF-I concentration was assessed by
a solid-phase, enzyme-labelled chemiluminescent
immunometric assay, (IMMULITE, DPC), calibrated to WHO NIBSC 1st IRR 87/518, with analytical sensitivity 20 ng/mL, the calibration range up to
1600 ng/mL, the intra-assay CV 3.1-4.3% and the
inter-assay CV 5.8-8.4%. For comparison among
children with different age and sex, IGF-I concentrations were expressed as SD score (IGF-I SDS),
according to DPC reference data, regarding IGF-I
concentration as decreased when IGF-I SDS was
below –1.0.
Statistical analysis included the comparison of
IGF-I concentrations in particular time points of the
test with the use of statistical tests for dependent
samples (t-Student’s test, Wilcoxon’s test), as well
as the h assessment of correlation coefficients.
The study was approved by local Ethic Committee of Polish Mother’s Memorial Hospital – Research Institute.
Results
Significant progressive increase of IGF-I secretion (expressed as both IGF-I concentration and
IGF-I SDS) was observed during the test. The differences between IGF-I concentrations in samples
0 and 1 as well as in samples 1 and 4 were significant (p<0.0001), while those between samples 4
and 7 remained insignificant. The obtained results
are shown in Table I and in Figure 1.
A significant correlation (p<0.05) was found between both IGF-I concentrations and IGF-I SDS in
subsequent time points (i.e. between samples 0 and
1, samples 4 and 1, as well as samples 7 and 4). The
strongest correlation was found both between IGF-I
concentration and IGF-I SDS in samples 4 and 7
(r=0.86, p<0.05) and in samples 0 and 1 (r=0.85,
p<0.05), as shown in Figures 2-4.
After 4 doses of rhGH, the increase of IGF-I
concentration ranged from 25.1 ng/mL to 551 ng/
mL (from 51% to 374% of initial value), in 8 of the
patients not exceeding 100 ng/mL. In the child with
the lowest IGF-I response to rhGH application, the
extension of the test up to 7 days caused only a minimal increase of IGF-I concentration (from 25.1
to 28.0 ng/mL). In most of patients, i.e. in 29 children (72.5%) after 4 rhGH doses and in 33 children
(82.5%) after 7 doses the increase of IGF-I concentration was higher than 100% of the initial value.
Normal IGF-I concentration (i.e. IGF-I SDS over
–1.0) after 4 days of rhGH application was obtained
in 35 children (87.5%), while after next 3 injections
only in 1 child more.
Discussion
Insulin-like growth factor-I generation test (previously known as smoatomedin generation test) was
introduced as an examination enabling for either
confirmation or exclusion GH insensitivity, accepting only a slight increase of IGF-I secretion as sufficient to exclude GH resistance. However, different
criteria of normal response to rhGH application
are still approved and used. For example, IGF-I
concentration increase during standard 4-day long
generation test sufficient to exclude GH insensitiv-
Table I. IGF-I concentrations in particular time points of the test
Tabela I. Stężenia IGF-I w poszczególnych punktach czasowych testu
sample 0
sample 1
sample 4
sample 7
IGF-I [ng/mL]
138,7±48
198,0±85,2
342,1±147,9*
373,4±162,3*
IGF-I SDS
-2,15±0,83
-1,35±0,97
-0,04±0,95#
0,17±0,94#
all the differences except for those marked * and # highly significant (p<0.0001)
wszystkie różnice z wyjątkiem oznaczonych * i # wysoce znamienne (p<0,0001)
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Praca oryginalna
Endokrynol. Ped., 6/2007;3(20):27-33
a, b, c – significant differences (p<0.0001)
a, b, c – różnice znamienne (p<0,0001)
Figure 1. IGF-I SDS values in particular time points of the test
Rycina 1. Wartości IGF-I SDS w poszczególnych punktach czasowych testu
Figure 2. Correlation between IGF-I SDS values in time points (samples) 0 and 1
Rycina 2. Korelacja pomiędzy wartościami IGF-I SDS w punktach czasowych (próbkach) 0 i 1
30
Smyczyńska J. i inni – Reliability of 4-day Variant of Insulin-like Growth Factor-I Generation Test...
Figure 3. Correlation between IGF-I SDS values in time points (samples) 1 and 4
Rycina 3. Korelacja pomiędzy wartościami IGF-I SDS w punktach czasowych (próbkach) 1 i 4
Figure 4. Correlation between IGF-I SDS values in time points (samples) 4 and 7
Rycina 4. Korelacja pomiędzy wartościami IGF-I SDS w punktach czasowych (próbkach) 4 i 7
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Praca oryginalna
ity varied from 20 ng/mL, according to Tetlow et
Clayton [5] to 100 ng/mL, according to Buckway et
al. [8]. Darendeliler et al. [7] established a slightly
higher cut-off value of IGF-I increase on the level
of 2.0 nmol/L (115 ng/mL). Next, Blair et al. [6]
and Cotteril et al. [10] regarded IGF-I increase as
low, not exceeding the doubled value of the coefficient of variation of the assay. Thus, for the kits
used in the current study, the cut-off value for IGF-I
increase should be established on the level of approximately 17%. In the current study – according
to the latter rule of interpretation of test results – the
increase of IGF-I secretion after 4 doses of rhGH
was sufficient to exclude IGF-I resistance in all the
patients. It should be mentioned that the strong correlation between IGF-I concentrations after 4 and 7
doses of rhGH confirmed the equivalency of both
test protocols, while the similar correlation between
IGF-I concentrations before rhGH application and
after 1st injection indicated poor effect of a single
dose of rhGH on IGF-I synthesis.
Recent studies on IGF-I kinetics after rhGH application are only sparse. The most detailed review
was published in 1997 by Lee et al. [11]. In 1984
D’Ercole et al. [12] showed that IGF-I increase
started about 4 hours after GH injection, almost
simultaneously with the achievement of maximal
GH concentration in serum. Next, Snyder et al. [13]
and Valk et al. [14] stated that stable IGF-I serum
concentration was achieved after 1-2 weeks of daily
GH injections. The unchanged IGF-I concentration
was observed for 24 hours after last GH dose [15].
In 2001, Buckway at al. [8] presented the results of IGF-I generation test, performed in healthy
subjects – children and adults – with 2 different
daily doses of rhGH: 0.05 mg/kg (i.e. 0.15 IU/kg)
and 0.025 mg/kg (i.e. 0.075 IU/kg). A significant
increase of IGF-I concentration was found after 4
doses of rhGH in all the age groups of both male
and female subjects, while further increase of IGF-I
secretion in subsequent days of the test remained
insignificant. Interestingly, the response of IGF-I
to rhGH administration turned out dose-independent. In that study, in most of GH-deficient patients
the increase of IGF-I was significant after both 4
and 7 rhGH application, while in 26% of cases the
response to rhGH administration was below 100
ng/mL, being regarded as poor. In our study, IGF-I
secretion was assessed in the same time points and
an “intermediate” daily dose of rhGH (0.1 IU/kg)
was applied. The poor response to rhGH, according
to the same criteria, was found in 20% of patients.
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Endokrynol. Ped., 6/2007;3(20):27-33
In our opinion, however, the assessment of IGF-I
increase during generation test should take into
consideration the reference data for patient’s age
and – particularly – normalisation of previously
decreased IGF-I level. Under such criteria, normal
values of IGF-I SDS were obtained in 87.5% of
patients. It should be stressed that the patients in
our study were short but no GH-deficient, having
normal GH secretion in stimulating tests.
It seems that administration of rhGH in a daily
dose of 0.1 IU/kg during 4 days is sufficient to obtain reliable results of IGF-I generation test. The increase of IGF-I concentration up to normal value for
age and sex (i.e. IGF-I SDS achieved after 4 doses
of rhGH over –1.0) seems to be a credible marker of
good response to rhGH.
The most important problem in clinical practice
seems to be the relationship between a short-term
increase of IGF-I secretion in response to rhGH
administration and long-term effectiveness of GH
therapy. The data, concerning that issue are rather
scarce and non-consistent. Jorgensen et al. [16] stated that there was no evidence of a correlation between IGF-I and the effects of GH replacement, as
positive correlation between a short-term increase
in serum IGF-I and height velocity was found in
the minority of studies. Furthermore, the increase
of IGF-I secretion after rhGH administration was
observed not only in GH-deficient subjects, but
also in healthy, normally growing ones [8]. On the
other hand, the results presented by Lee et al. [11]
indicated long-term stability of IGF-I concentration on the level close to that achieved during the
initial phase of rhGH therapy. Moreover, Kamp
et al. [17] stated that the response to high dose of
rhGH was a good predictor of growth response to
the therapy. Preliminary results of our studies on
IGF-I secretion during short- and long-term rhGH
administration (unpublished) seem to confirm these
observations, indicating a good correlation between
IGF-I concentration after 1 week, 3 and 6 months,
and 1 year of rhGH therapy. Moreover, in our material, the increase of IGF-I concentration presented
similar in short children with either decreased or
normal GH secretion in stimulating tests [18]. What
is more, long-term studies seem necessary to assess
the effectiveness of rhGH therapy in such patients.
The study was supported by Ministry of Science
and Informatization, Project No 2P05E 030 028
Smyczyńska J. i inni – Reliability of 4-day Variant of Insulin-like Growth Factor-I Generation Test...
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