Growth Hormone Responses to Provocative Tests in Children with Short Stature

Abstract

Growth hormone deficiency (GHD) is defined as a serum peak GH concentration <10 ng/mL with provocation as tested by a combination of at least two separate tests. The aim of this study was to compare two standard tests, insulin and levodopa (L-dopa), with a primary focus on specificity and accuracy. Clinical data were collected retrospectively from a review of 120 children who visited the pediatric endocrine clinic at Chonnam National University Hospital for the evaluation of short stature between January 2006 and April 2014. Subjects underwent GH provocation tests with insulin and L-dopa. Blood samples were obtained at 0, 15, 30, 45, 60, 90, and 120 min after administration, and GH levels were measured. In the insulin test, serial glucose levels were also checked, closely monitoring hypoglycemia. A total of 83 children (69.2%) were diagnosed with GHD and 37 children (30.8%) were diagnosed with idiopathic short stature (ISS). Peak GH levels were achieved an average of 45 min after the administration of insulin and L-dopa for both groups. The specificity and accuracy were 78.4% and 93.6% for the insulin test and 29.7% and 79.2% for L-dopa test, respectively. In the ISS group, the cumulative frequency of a GH cutoff value of >10 ng/mL at 120 min was 75.6% after insulin stimulation compared with 35.1% after L-dopa stimulation. Considering these results, we recommend performing the insulin test first to exclude ISS and then the L-dopa test for the diagnosis of GHD. This way, ISS patients are diagnosed after a single test, thus reducing hospital days and the burden of undergoing two serial tests.

Full text

33
Original Article
www.cmj.ac.k
r
http://dx.doi.org/10.4068/cmj.2015.51.1.33
Ⓒ Chonnam Medical Journal, 2015
Chonnam Med J 2015;51:33-38
Growth Hormone Responses to Provocative Tests in Children
with Short Stature
Noorisaem Rhee, Ka Young Oh, Eun Mi Yang and Chan Jong Kim
*
Department of Pediatrics, Chonnam National University Medical School and Hospital, Gwangju, Korea
Growth hormone deficiency (GHD) is defined as a serum peak GH concentration ＜10
ng/mL with provocation as tested by a combination of at least two separate tests. The
aim of this study was to compare two standard tests, insulin and levodopa (L-dopa),
with a primary focus on specificity and accuracy. Clinical data were collected retro-
spectively from a review of 120 children who visited the pediatric endocrine clinic at
Chonnam National University Hospital for the evaluation of short stature between
January 2006 and April 2014. Subjects underwent GH provocation tests with insulin
and L-dopa. Blood samples were obtained at 0, 15, 30, 45, 60, 90, and 120 min after
administration, and GH levels were measured. In the insulin test, serial glucose levels
were also checked, closely monitoring hypoglycemia. A total of 83 children (69.2%) were
diagnosed with GHD and 37 children (30.8%) were diagnosed with idiopathic short stat-
ure (ISS). Peak GH levels were achieved an average of 45 min after the administration
of insulin and L-dopa for both groups. The specificity and accuracy were 78.4% and 93.6%
for the insulin test and 29.7% and 79.2% for L-dopa test, respectively. In the ISS group,
the cumulative frequency of a GH cutoff value of ＞10 ng/mL at 120 min was 75.6% after
insulin stimulation compared with 35.1% after L-dopa stimulation. Considering these
results, we recommend performing the insulin test first to exclude ISS and then the
L-dopa test for the diagnosis of GHD. This way, ISS patients are diagnosed after a single
test, thus reducing hospital days and the burden of undergoing two serial tests.
Key Words: Growth hormone; Dwarfism; Child
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial
License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use,
distribution, and reproduction in any medium, provided the original work is properly cited.
Article History:
received 6 March, 2015
revised 31 March, 2015
accepted
3 April, 2015
Corresponding Author:
Chan Jong Kim
Department of Pediatrics, Chonnam
National University Medical School
and Hospital, 42 Jebong-ro,
Dong-gu, Gwangju 501-757, Korea
TEL: +82-62-220-6645
FAX: +82-62-222-6103
E-mail: cjkim@jnu.ac.kr
INTRODUCTION
The diagnosis of growth hormone deficiency (GHD) in
children with short stature is based on clinical features.
Children with GHD usually present with short stature and
a low growth velocity for age and pubertal stage.
1,2
Alterna-
tive causes of poor growth need to be considered and ex-
cluded. One of the normal variants is idiopathic short stat-
ure, a group of short children with no definitely recogniz-
able underlying disease. It is important to distinguish be-
tween the child with GH deficiency and the short normal
child.
GH secretion is regulated by multiple physiologic fac-
tors, including age, onset of puberty, nutritional status,
and body weight.
3-6
GH secretion is pulsatile and serum
concentrations are low during the daytime. Thus, provoca-
tive tests of GH release, rather than a single basal GH esti-
mation, are used to determine GH status. Immunoradio-
metric assays (IRMAs) are commonly used to determine
the level of GH.
7
The standard method for the diagnosis of GH deficiency
is to confirm insufficient responses to GH provocation
tests. GH deficiency is defined as a serum peak GH concen-
tration ＜10 ng/mL on provocation with a combination of
at least two separate stimulation tests.
8,9
GH stimulation
tests are performed with various stimuli, such as insulin,
L-dopa, arginine, and growth hormone releasing hormone
(GHRH).
10
The test using insulin as a stimulus is classi-
cally recommended, but this test has potential risks such
as hypoglycemia. In this study, we compared two standard
provocation tests, insulin and L-dopa, with a primary focus
on specificity, accuracy, and safety.

34
Growth Hormone Responses to Provocative Tests in Children
TABLE 1. Clinical and biochemical parameters of patients with GHD or ISS
GHD group (N=83) ISS group (N=37) p value
Gestational age (wk)
Birth weight (kg)
Chronological age (yr)
Bone age (yr)
CA-BA (yr)
Height age (yr)
Height SDS
MPH (cm)
Body weight SDS
BMI SDS
IGF-1 (ng/mL)
IGFBP-3 (ng/mL)
Peak GH-L (ng/mL)
Peak GH-I (ng/mL)
39.44±2.00
2.98±0.46
9.99±2.60
9.05±2.63
0.69±0.57
7.13±2.29
−2.60±0.08
164.59±6.94
−1.59±0.11
−0.25±0.13
171.86±96.95
2431.40±656.96
5.17±2.63
4.03±2.60
39.56±0.89
3.05±0.48
9.64±2.78
8.61±2.60
0.69±0.81
6.66±2.11
−2.69±0.10
164.73±6.80
−2.31±0.14
−0.98±0.16
170.75±98.60
2677.87±889.49
10.62±8.37
14.71±8.78
0.646
0.473
0.521
0.392
0.998
0.276
0.499
0.920
＜0.001
0.001
0.954
0.136
＜0.001
＜0.001
V
alues are presented as mean±standard deviation (SD). GHD: growth hormone deficiency, ISS: idiopathic short stature, CA: chrono
-
logical age, BA: bone age, SDS: standard deviation score, MPH: midparental height, BMI: body mass index, IGF-1: insulin-like growt
h
factor-1, IGFBP-3: IGF binding protein-3, Peak GH-L: L-dopa, Peak GH-I: insulin.
MATERIALS AND METHODS
1. Subjects
This retrospective study was done by reviewing the med-
ical records of children who visited the pediatric endocrine
clinic at Chonnam National University Hospital. A total of
120 children with short stature who completed a GH stim-
ulation test from January 2006 to April 2014 were enrolled
in this study. All patients had a height less than the third
percentile. Children with central nervous system neo-
plasms, multiple pituitary hormone deficiencies, and hy-
pothyroidism were excluded. Children who had been tak-
ing drugs that may affect endogenous GH secretion, such
as antipsychotic drugs and corticosteroids, and children
with congenial disorder (e.g., Russel-Silver syndrome)
were also excluded.
GH deficiency was defined as a serum peak GH concen-
tration ＜10 ng/mL on provocation with a combination of
at least two separate stimulation tests. Idiopathic short
stature (ISS) was classified as a height less than the third
percentile with a serum peak GH concentration ≥10 ng/mL
with provocation.
Data for height, weight, pubertal status, insulin-like
growth factor (IGF-1), insulin-like growth factor binding
protein (IGFBP)-3, thyroid function, and peak GH levels
after stimulation were collected. Pubertal status was as-
sessed by Tanner stage of breast development for females
and genital development for males. Bone age was eval-
uated by the method of Greulich and Pyle.
11
All GHD sub-
jects had normal magnetic resonance imaging findings of
the hypothalamic-pituitary region. This study was ap-
proved by the Institutional Review Board of our hospital
(CNUH-2014-295).
2. GH stimulation test
After an overnight fast, an intravenous cannula was
inserted. All provocation tests were performed in the morn-
ing hours with a 1-day interval between the two stimulation
tests. To assess GH secretion, dopamine (Sinemet
Ⓡ
, MSD,
Whitehouse Station, NJ, USA; body weight more than 30
kg, 500 mg; body weight 15 to 30 kg, 250 mg; body weight
less than 15 kg, 125 mg of L-dopa) was administered orally.
Blood samples were drawn immediately before the medi-
cation and 30, 45, 60, 90, and 120 minutes later to obtain
the serum GH concentration for each time point. Insulin
(0.1 IU/kg) was administered as an intravenous bolus at
time 0 to induce a fall in the blood glucose level to 50 mg/dL
or less (or one-half of the baseline glucose level). Blood sam-
ples were obtained immediately before injection and at 15,
30, 45, 60, 90, and 120 minutes after injection. No patients
were primed with sex steroids before the provocation tests.
3. Hormone assays
GH levels were measured by IRMA with the detection
limit of 0.03 IU/mL. The intra-assay coefficients of varia-
tion (CVs) were 1.3% to 2.1%, and the inter-assay CVs were
3.8% to 5.0% (Cisbio Bioassays, France). Serum IGF-1 lev-
els were measured by using an IRMA with an analytical
sensitivity of 2 ng/mL, intra-assay CV of 2.4% to 6.3%, and
inter-assay CV of 5.3% to 6.8% (IRMA IGF-1, Immunotech,
Czech Republic). Serum IGFBP-3 levels were measured by
using an IRMA with an analytical sensitivity of 50 ng/mL,
intra-assay CV of 4.6% to 10.2%, and inter-assay CV of 6.3%
to 12.4% (IDS S.A, Belgium).
4. Analysis
Categorical data were described as number (percentage)
and continuous data were presented as the mean±standard
deviation (SD). Comparisons between groups were per-
formed by using independent-sample t-tests. Statistical
significance was defined as p＜0.05. Statistical analysis
was performed by using SPSS (version 22.0; SAS Institute,

35
Noorisaem Rhee, et al
FIG. 1. Comparison of peak GH concentrations following L-dopa (A) and insulin (B) stimulation tests between the GHD patients (n=83)
and the ISS patients (n=37). Box-plots show the median, interquartile range, outliers, and extreme cases. GH: growth hormone, GHD
:
growth hormone deficiency, ISS: idiopathic short stature.
FIG. 2. Comparison of GH concentrations at each time point after L-dopa (A) and insulin (B) stimulation tests between the GHD and
ISS patients. Data are presented as median and 95% confidence interval (CI). GH: growth hormone, GHD: growth hormone deficiency,
ISS: idiopathic short stature.
Chicago, IL, USA) and GraphPad Prism (version 5;
GraphPad Software Inc, La Jolla, CA, USA). Specificity
was defined as the number of true negative results divided
by the total number of results. Accuracy was defined as the
number of correct results divided by the total number of
tests.
RESULTS
1. Subjects’ characteristics
The clinical and laboratory data are summarized in
Table 1. Of the 120 children who underwent the GH stim-
ulation test, 83 children (69.2%) were diagnosed with GHD
and 37 children (30.8%) were diagnosed with ISS. A total
of 83 children (69.2%) were boys and 37 (30.8%) were girls.
The mean age of the children was 9.99±2.60 years in the
GHD group and 9.64±2.78 years in the ISS group. A total
of 92 children (76.7%) were prepubertal (Tanner stage 1)
and 28 children (23.3%) were pubertal (Tanner stage 2 or
3). The IGF-1 and IGFBP-3 level of the patients at the time
of the stimulation test showed no significant difference in
either group. In the GHD group, the mean IGF-1 level was
171.86±96.95 ng/mL, similar to that in the ISS group
(170.75±98.60 ng/mL, p=0.954).
The mean body weight standard deviation score (SDS)
of the GHD group was −1.59±0.11, which was higher than
that of the ISS group of −2.31±0.14, which was a statisti-
cally significant difference (p＜0.001). Also, the mean body
mass index (BMI) SDS of the GHD group was higher (−
0.25±0.13) than the mean BMI SDS of the ISS group (−
0.98±0.16, p=0.001; Table 1).
2. Comparison of peak GH levels
Peak GH levels were achieved on average 45 min after
the administration of insulin and L-dopa in both groups.
In the test with insulin (peak GH-I), the mean peak GH lev-
el of the ISS group (14.71±8.78 ng/mL) was significantly
higher than that of the GHD group (4.03±2.60 ng/mL, p
＜0.001). Also, in the test with L-dopa (peak GH-L), the
mean peak GH level of the ISS group (10.62±8.37 ng/mL)

36
Growth Hormone Responses to Provocative Tests in Children
TABLE 2. Frequency (%) of a growth hormone cutoff value of ＞10 ng/mL at each time point during the L-dopa and insulin stimulatio
n
test in patients with idiopathic short stature
Basal 15 min 30 min 45 min 60 min 90 min 120 min
L-dopa
Cross-sectional (%)
Cumulative (%)
Insulin
Cross-sectional (%)
Cumulative (%)
0 (0)
0 (0)
0 (0)
0 (0)
-
-
7 (18.9)
7 (18.9)
2 (5.4)
2 (5.4)
13 (35.1)
14 (37.8)
9 (24.3)
9 (24.3)
14 (37.8)
21 (56.7)
3 (8.1)
10 (27.0)
13 (35.1)
24 (64.8)
3 (8.1)
11 (29.7)
7 (18.9)
27 (72.9)
4 (10.8)
13 (35.1)
3 (8.1)
28 (75.6)
TABLE 3. Comparison of specificity and accuracy of insulin and
L-dopa stimulation test
Specificity (%) Accuracy (%)
Insulin
L-Dopa
78.4
29.7
93.6
79.2
was significantly higher than that of the GHD group (5.17±
2.63 ng/mL, p＜0.001; Fig. 1).
The mean peak time was on average 45 min for both
groups for both tests. We also compared the peak GH con-
centrations versus time after the L-dopa and insulin stim-
ulation tests between the GHD and ISS patients (Fig. 2).
In both tests, the peak GH concentration was much higher
in the ISS group.
Table 2 shows the differences between the cross-sectional
and cumulative frequency of a GH cutoff value of ＞10
ng/mL at each time point during the insulin and L-dopa
stimulation tests in ISS patients. The cumulative fre-
quency at 120 min was 75.6% after insulin stimulation
compared with 35.1% after L-dopa.
Also, we compared the specificity and accuracy of the two
tests. In the case of insulin, the specificity was 78.4% and
the accuracy was 93.6%. On the other hand, the specificity
for the L-dopa stimulation test was 29.7% and the accuracy
was 79.2% (Table 3).
DISCUSSION
Children with short stature visit the outpatient depart-
ment for the evaluation of short stature and reduced
growth velocity. The diagnosis of GHD is classically based
on clinical features, but can only be confirmed by a GH stim-
ulation test using different stimuli.
12
Because GH secretion
is regulated by multiple physiologic factors, including age,
onset of puberty, nutritional status, and body weight, the
reliability of the pharmacological tests used for the evalua-
tion of GH secretion has been repeatedly questioned.
13,14
However, the GH stimulation test is still considered to be
the gold standard when diagnosing GHD. It is defined as
a serum peak GH concentration ＜10 ng/mL on provocation
with the combination of at least two separate stimulation
tests.
15-17
Classically, a child whose height is below the third per-
centile will undergo a GH stimulation test using L-dopa
and insulin. A diagnosis is made by assessing the peak GH
level.
18
If the peak GH level is higher than 10 ng/mL, at any
time point on a single test, the child is diagnosed as having
ISS.
19,20
In both tests with L-dopa and insulin, the mean
peak GH level of ISS children was significantly higher than
that of the children with GHD.
A relationship exists between body weight, BMI, and
GHD. The mean body weight SDS of the GHD group was
−1.59±0.11, which was higher than that of the ISS group
of −2.31±0.14 (p＜0.001), and the mean BMI SDS of the
GHD group was higher (−0.25±0.13) than that of the ISS
group (−0.98±0.16, p=0.001). According to a recent study,
BMI is one of the predictors of peak GH.
21
Stanley et al. dem-
onstrated that the peak GH response to a provocative test
decreases with increasing BMI SDS in healthy children
with short stature.
22
A higher BMI is associated with lower
GH secretion.
23-25
The peak GH concentration was higher in the ISS group
but the time to the peak GH level was similar in both groups
(mean peak time of 45 min). There were differences be-
tween the cross-sectional and cumulative frequency of the
GH cutoff value of ＞10 ng/mL at each time point during
the insulin and L-dopa stimulation tests in ISS patients.
As shown in Tables 2 and 3, the cumulative frequency at
120 min was 75.6% after insulin stimulation compared
with 35.1% after L-dopa stimulation. Thus, we suppose
that the stimulation test with insulin is better for diagnos-
ing ISS than the test with L-dopa.
One of the most important results of this study was the
difference in specificity and accuracy between the two prov-
ocation tests (Table 3). Also, the frequency (%) of a GH con-
centration ＞10 ng/mL in the ISS group was higher with
the insulin test (75.6%) than with the L-dopa test (35.1%).
This result suggests that it would be beneficial to perform
the ISS test first before the L-dopa test. In this way, ISS
patients who show a peak GH ＞10 ng/mL can be ruled out
by use of a single test.
The provocation tests have some side effects because of
the drugs used as stimuli.
26
L-Dopa can cause adverse re-
actions, commonly gastrointestinal problems (e.g., nau-
sea, vomiting), and insulin has the potential to induce seri-
ous hypoglycemia. Thus, close monitoring for adverse re-
actions, especially for hypoglycemia during a provocation
test using insulin, is needed.
27,28
In our study, among the

37
Noorisaem Rhee, et al
120 patients who underwent the insulin stimulation test,
the lowest serum glucose level was less than 40 mg/dL in
58 patients, and 119 patients showed a glucose concen-
tration under 50 mg/dL. The mean glucose level was 38.5
mg/dL. In a total of 71 patients (59.1%), the lowest glucose
level was recorded at 20 min after insulin administration
(mean, 21.6 min). The most common hypoglycemic symp-
tom was dizziness, and these patients recovered soon after
drinking juice or eating candy. However, one patient with
serious hypoglycemia (serum glucose, 21 mg/dL) showed
mental change (drowsy mental status) and recovered after
intravenous administration of 10% dextrose water.
Considering the outcomes, although the insulin test has
the potential to evoke hypoglycemia, we suggest perform-
ing the insulin stimulation test first to rule out ISS (with
close monitoring for hypoglycemic symptoms) and then the
L-dopa test for the remaining patients to confirm the GHD.
This is cost-effective because the diagnosis of ISS can be
made shortly after a single test. Also, the burden of doing
two serial tests is reduced.
CONFLICT OF INTEREST STATEMENT
None declared.
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