INTRODUCTION:Premature thelarche in girls younger than 4 years of age is a cause for clinical concern and requires reliable assessment tools. Current guidelines, for decision-making and management of girls with premature thelarche in Sweden are based on serum estradiol determination performed by sensitive extraction radioimmunoassay (RIA). However, the extraction RIA has been replaced by a high-sensitivity mass spectrometry (MS)-based estradiol method. The primary aim of the present study was to evaluate the performance of the MS-based method in comparison with extraction RIA. METHODS:In a prospective observational study, 43 serum samples from girls with premature thelarche aged 6-48 months were run in parallel for comparison between the phased-out extraction RIA and the newer high-sensitivity MS-based assay. The lower limits of detection were 4 pmol/L for both methods. RESULTS:There was a significant correlation between the two methods, r=0.67, p=0.000. The MS-based method yielded a mean of 5.3 (±2.7) pmol/L lower concentrations compared to extraction RIA. CONCLUSION:The estradiol upper limit level for what is considered benign in premature thelarche, obtained with extraction RIA, needs to be lowered when analyzed with high sensitivity MS-based methods.

OBJECTIVES:To evaluate changes in health-related quality of life in boys aged 14-16 years with delayed or slowly progressing puberty before and after low-dose testosterone treatment. Delayed puberty can cause short stature, emotional distress, and social challenges. Testosterone therapy promotes growth and masculinization, but its impact on quality of life remains poorly understood. Few studies have assessed psychosocial outcomes using validated instruments. METHODS:Twenty-seven boys enrolled in the Pubertal Replacement in Boys Study and were randomized to testosterone enanthate (75 mg/month for 6 months; n=12) (n=12) or testosterone undecanoate (n=12) (250 mg every 3 months; n=15). Standardized self-report questionnaires assessed generic quality of life (primary outcome), stature-specific quality of life, depressive symptoms, and enjoyment of physical activity. Assessments were conducted at baseline, 6 months, and 12 months. RESULTS:Twenty-six boys completed the study. Both regimens induced pubertal progression and a mean growth of 9.3 cm 12 months after start of replacement treatment. Significant improvements were observed in generic quality of life and depressive symptoms, with early gains sustained through 12 months. No changes were detected in stature-specific quality of life or enjoyment of physical activity. No statistical differences were found between treatment groups at 6 or 12 months. Exploratory analyses suggested that baseline testosterone serum levels were modestly associated with changes in social functioning, whereas later serum levels showed no such relationship. CONCLUSIONS:Low-dose testosterone therapy improves generic quality of life and mood in boys with self-limited delayed puberty, likely reflecting successful pubertal progression. These findings highlight the importance of psychosocial outcomes as indicators of treatment success, beyond growth acceleration, and support structured follow-up to address the emotional needs of adolescents with delayed puberty.

ContextThe use of testosterone enanthate (TE), 50–75 mg intramuscularly (i.m.)/month, for the treatment of boys with delayed puberty or slow progression to induce puberty is the standard of care (SoC) in Sweden. This treatment is empirical and has not been scientifically evaluated. Replacement therapy in hypogonadal boys/young men in Sweden after induction is mainly performed with testosterone undecanoate (TU), 1,000 mg/3 months. TE is only available on license. TE was deregistered in Sweden in 2006. Therefore, this study was initiated to compare the two products.ObjectiveTo clinically evaluate pubertal progression with six injections of TE, 75 mg i.m./month (1/3–1/5 of adult dose), compared with two injections of TU, 250 mg i.m./3 months (1/4 of adult dose).Trial designIn the Pubertal Replacement in Boys Study (PRIBS), boys aged 14–16 years in West Sweden with pubertal delay were randomized in a parallel study to TE or TU for pubertal progression. Inclusion criteria were morning testosterone levels of 0.5–3 nmol/L and testicular volume ≤6 ml. Between June 2014 and Nov 2019, 27 boys were included.MethodsThe primary outcome was testicular enlargement ≥8 ml after 12 months. TU treatment was considered clinically similar if the number of boys with testicular enlargement ≥8 ml was 80%–125% of the number of boys with TE. Fisher’s exact chi-square test was used for this analysis.ResultsBoth treatments were well tolerated. Twelve of 14 (86%) TU-treated boys reached the primary outcome and 12/12 in the TE group. Fisher’s exact chi-square testing indicated a one-sided p-value of 0.28 (the two-sided p-value was 0.483). The TU treatment was considered not clinically different from SoC. A post-hoc study showed 25% power. Therefore, no evidence-based conclusion can be drawn from the results even if the clinical data support a similar effect of the treatments.ConclusionThe present small-scale study supports that both TE and TU had similar effects in terms of pubertal progression.Clinical Trial Registrationhttps://www.clinicaltrials.gov/ct2/home, identifier NCT05417035; https://www.clinicaltrialsregister.eu/ctrsearch/search, identifier EUDRACTEudraCT nr 2012-002337-11.

BACKGROUND:Since there are few treatment options for young people with type 2 diabetes, we aimed to assess the efficacy and safety of dapagliflozin as add-on therapy in children, adolescents, and young adults with type 2 diabetes receiving metformin, insulin, or both. METHODS:This multicentre, placebo-controlled, double-blind, randomised phase 3 study was undertaken at 30 centres in five countries (Hungary, Israel, Mexico, Russia, and the USA). Participants aged 10-24 years with type 2 diabetes and HbA1c concentration of 6·5-11% (48-97 mmol/mol) were randomly assigned 1:1 to oral dapagliflozin 10 mg or placebo during a 24 week double-blind period, which was then followed by a 28 week open-label safety extension in which all participants received dapagliflozin. Participants and study personnel were masked and participants were randomly assigned treatment (placebo or study drug) using an interactive web and voice response system. The primary outcome was between-group differences in change in HbA1c concentration from baseline to 24 weeks (intention-to-treat analysis). A prespecified sensitivity analysis of the primary outcome was also assessed in the per-protocol population, which included only protocol-compliant participants. This trial is registered with ClinicalTrials.gov, NCT02725593. FINDINGS:Between June 22, 2016, and March 15, 2019, 72 participants (19 [26%] of whom were aged 18-24 years) were randomly assigned (39 to dapagliflozin and 33 to placebo). Mean age was 16·1 (SD 3·3) years. In the intention-to-treat analysis, after 24 weeks, mean change in HbA1c concentration was -0·25% (95% CI -0·85 to 0·34; -2·7 [-9·3 to 3·7] mmol/mol) for dapagliflozin and 0·50% (-0·18 to 1·17; 5·5 [-2·0 to 12·8] mmol/mol) for placebo. The between-group difference was -0·75% (95% CI -1·65 to 0·15; -8·2 [-18·0 to 1·6] mmol/mol; p=0·10). In a sensitivity analysis in the per-protocol population (34 in the dapagliflozin group and 26 in the placebo group) after 24 weeks, mean change was -0·51% (-1·07 to 0·05; -5·6 [-11·7 to 0·5] mmol/mol) for dapagliflozin and 0·62% (-0·04 to 1·27; 6·8 [-0·4 to 13·9] mmol/mol) for placebo. The between-group difference was -1·13% (-1·99 to -0·26; -12·4 [-21·8 to -2·8] mmol/mol; p=0·012). Adverse events occurred in 27 (69%) dapagliflozin-assigned participants and 19 (58%) placebo-assigned participants over 24 weeks, and in 29 (74%) participants who received dapagliflozin over 52 weeks. Hypoglycaemia occurred in 11 (28%) dapagliflozin-assigned and six (18%) placebo-assigned participants who received dapagliflozin over 24 weeks and in 13 participants (33%) who received dapagliflozin over 52 weeks; none were considered as serious adverse events. No adverse events of diabetic ketoacidosis occurred. INTERPRETATION:The primary outcome of change in HbA1c concentration was not significant in the intention-to-treat analysis of children, adolescents, and young adults with type 2 diabetes receiving dapagliflozin in addition to standard-of-care treatment. A prespecified sensitivity analysis of protocol-compliant participants showed a significant difference in HbA1c concentration between groups. No new safety signals were identified and there was a low risk of severe hypoglycaemia. FUNDING:AstraZeneca.

Aims Trial protocols routinely exclude adolescents from enrolment in adult trials as 18 years is used as the minimum age eligibility criterion. Due to perceived vulnerability, trials for paediatric patients (children and/or adolescents) are often delayed until after the adult development has demonstrated a positive benefit-risk, relegating paediatric research until after a medicine is authorized for adult use. This approach stems from ethical debates that children must be further protected from unnecessary risks of harm. Across regional jurisdictions, adolescence is typically determined utilizing chronological age, often reflecting the legal age of majority in that region. Globally, the legal definition of adolescence roughly corresponds with the period of time between the ages of 10 and 20 years of life. Adolescence, however, is a period of development characterized by sexual maturation, a variable and accelerated rate of growth and continued neurocognitive development. Methods We evaluated regional and international regulatory guidance and statute for their definition of the adolescent population. In addition to the legal age of majority, we identified two key thematic categories that underscore the adolescent definitions utilized globally - behavioral and developmental/physiological. Leveraging these themes, the research team developed a user-friendly adolescent inclusion decision-tree for use by sponsors, investigators, ethics committees, and reviewing health agencies as they evaluate study protocols. The tool combines a series of considerations that evaluate developmental, therapeutic and disease-related characteristics as a more relevant scientific basis than age alone to inform the appropriateness of adolescent cohorts in adult research. The tool guides users to evaluate seven key as a means to facilitate robust consideration of the role for adolescent inclusion in adult research. These topics include: • Disease • Product • Statistical • Operational • Investigator & Site-focused • Sponsor-focused • Legal & Ethical Results Beta-testing of the tool was launched in January 2022. Testers (academia researchers, coordinators, industry, ethics committee members) have been asked to evaluate each topic section on its unique merits and to assess the tool comprehensively on whether the sections address all elements crucial to age-inclusive research. The objective is to assess the tool for its: 1. Functionality (how ‘useful’ is the tool in your role?) 2. Interpretability (how ‘understandable’ is each component of the tool?) 3. Usability (how ‘easy’ is the tool to use?) Identification of gaps (critical errors of omission) are also intended to be captured. Insights gained during beta-testing will be utilized by the research team to enhance the functionality, interpretability and usability of the adolescent inclusion decision-tree. Conclusion We encourage trial sponsors, investigators, regulators, and ethics committees to challenge research orthodoxy related to adolescent inclusion in adult research and seek trial solutions grounded in science rather legal definitions of age alone. We developed an adolescent inclusion decision tree to facilitate discourse on trial design considerations that facilitate the more timely inclusion of adolescents in research. Inclusion of adolescents within appropriate adult studies not only facilitates the generation of data for use in determination of benefit-risk in the adolescent population, it can also serve as a meaningful pathway to facilitate earlier access for adolescents to efficacious therapies.

The article How is the Pharmaceutical Industry Structured to Optimize Pediatric Drug Development? Existing Pediatric Structure Models and Proposed Recommendations for Structural Enhancement, written by Thomas Severin et al. was originally published electronically on the publisher's internet portal on February 6, 2020 without open access. With the author(s)' decision to opt for Open Choice the copyright of the article changed on April 22, 2020 to © The Author(s) 2020 and the article is forthwith distributed under a Creative Commons Attribution 4.0 International License https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Objective: The aim of this work was to investigate the prevalence of premature thelarche (PT) in 18-month-old girls, and the incidence of clinically evaluated PT for girls aged 18–36 months. Methods: In the prevalence substudy, a prospective population-based cohort of 3,140 girls born at Northern Älvsborg county hospital (NÄL) in Trollhättan, Sweden, was followed for 2 years. Girls with breast development at the 18-month health check were referred to one pediatric center in NÄL for evaluation. All girls with PT were included and followed for clinical outcome and 17β-estradiol. The prospective incidence substudy covered 8 years in a 10-year period and included all girls aged 18–36 months born at NÄL who were clinically evaluated for PT. Results: The prevalence of PT at 18 months in our cohort was 1.6/1,000. The 5 girls with PT no longer showed symptoms at the follow-up 3–6 months later. The incidence was 1.1/1,000 for girls aged 18–36 months and 1.0/1,000 for girls aged 18–30 months who were clinically evaluated for their PT. Conclusion: This is the first prospective population-based study of PT and it shows a prevalence of PT at age 18 months of 1.6/1,000. The incidence of clinically evaluated PT was 1.1/1,000. Our result is in line with other studies reporting the incidence of PT from medical records (0.4–40/1,000). The outcome of PT in our study, as in the other studies, is that the great majority of girls show only benign symptoms.

Background: Most girls with Turner syndrome (TS) require pubertal induction with estrogen, followed by long term replacement. However, no adequately powered prospective studies comparing transdermal with oral 17β-estradiol administration exist. This reflects the difficulty of securing funding to study a rare condition with relatively low morbidity/mortality when competing against conditions such as cancer and vascular disease. Protocol Consensus: The TS Working Group of the European Society for Paediatric Endocrinology (ESPE) has agreed to both a 3-year oral and a 3-year transdermal regimen for pubertal induction. Prerequisites include suitable 17β-estradiol tablets and matrix patches to allow the delivery of incremental doses based on body weight. Study Proposal: An international prospective cohort study with single centre analysis is proposed in which clinicians and families are invited to choose either of the agreed regimens, usually starting at 11 years. We hypothesise that pubertal induction with transdermal estradiol will result in better outcomes for some key parameters. The primary outcome measure chosen is height gain during the induction period. Analysis: Assessment of the demographics and drop-out rates of patients choosing either oral or transdermal preparations; and appropriate analysis of outcomes including pubertal height gain, final height, liver enzyme and lipid profile, adherence/acceptability, cardiovascular health, including systolic and diastolic blood pressure and aortic root diameter and bone health. Conclusion: The proposed model of prospective data collection according to internationally agreed protocols aims to break the current impasse in obtaining evidence-based management for TS and could be applied to other rare paediatric endocrine conditions.

Background: Early onset of breast development in a young girl is usually a benign and isolated prepubertal condition, i.e., premature thelarche (PT), but can sometimes be progressive and the first sign of pubertal precocity (PP). Serum 17β-estradiol (17β-E2) level is a possible marker to differentiate between benign and pathological forms of breast development. We defined an upper serum 17β-E2 level for benign, “classic” PT for girls aged 9–48 months. Methods: Serum 17β-E2 was analysed with a highly sensitive extraction radioimmunoassay (RIA). Gonadotropins, Tanner breast stage, growth, other investigations, and clinical outcome were assessed in 125 girls with breast development, in a population-based study in West Sweden. Results: A total of 125 of 128 girls had a benign form of breast development with a mean serum 17β-E2 level of 15.2 pmol/L and a mean + 2 SD of 31 pmol/L, which was regarded as the upper limit for benign PT; 3 girls with PP had 17β-E2 levels above 70 pmol/L. Conclusion: This is the first study to define an upper serum 17β-E2 level associated with benign PT. Girls aged 9–48 months with PT and Tanner breast stage 2 have 17β-E2 levels below 32 pmol/L using extraction RIA. LH below the detection limit (0.1 IU/L) and measurable FSH support benign PT.

The overall goal of pubertal sex hormone replacement therapy (HRT) in girls is not only about development of secondary sexual characteristics, but also to establish an adult endocrine and metabolic milieu, as well as adult cognitive function. Estradiol (E2) is the first choice for HRT compared to ethinyl estradiol (EE2). E2 is the most potent endogenous estrogen in the circulation, with established levels during spontaneous puberty. Transdermal E2, compared to oral administration, is the first choice to start pubertal HRT. Transdermal application avoids liver exposure to supraphysiologic estrogen concentrations and provides a more physiologic mechanism for hormone delivery. By cutting E2 matrix patches in doses of 0.05-0.07 µg/kg or administrate E2 gel in doses of 0.1 mg/day, serum concentrations of E2 seen in early spontaneous puberty can be obtained. Patches can be removed in the morning and thereby mimic the normal circadian rhythm. For those clinics with access to sensitive E2 determinations methods (extraction followed by radioimmunoassay or mass spectrometry) monitoring the attained E2 serum levels is recommended in order to optimally mimic the levels seen in early puberty as well as growth velocity, breast and uterus development. Mid- and late pubertal HRT is obtained by increased doses of E2, adding cyclic oral or transdermal progestin, as well as testosterone gel over the pubic area if indicated.

Aims: We studied whether first morning voided (FMV) urinary gonadotropin measurements could be used as a noninvasive alternative to the GnRH test in the assessment of the hypothalamic-pituitary-gonadal function in children. Methods: In a single-center study, we compared FMV urinary gonadotropin concentrations with basal and GnRH-stimulated serum gonadotropin levels in 274 children and adolescents (78 girls, 196 boys) aged 5-17 years referred for growth and pubertal disorders. The concordance between FMV urinary gonadotropin concentrations and GnRH test results was assessed. Results: FMV urinary LH (U-LH), urinary FSH (U-FSH) and their ratios correlated well with the corresponding basal and GnRH-stimulated serum parameters (r ≥ 0.66, p < 0.001). Receiver operating characteristic curve analyses using urinary and serum LH and FSH concentrations showed that FMV U-LH and U-LH/U-FSH performed equally well as the GnRH test in the differentiation of early puberty (Tanner stage 2) from prepuberty (Tanner stage 1) (area under the curve 0.768-0.890 vs. 0.712-0.858). FMV U-LH and U-LH/U-FSH performed equally well as basal serum LH in predicting a pubertal GnRH test result (area under the curve 0.90-0.93). Conclusion: FMV U-LH determination can be used for the evaluation of pubertal development and its disorders, reducing the need for invasive GnRH stimulation tests.

Background. Immunoassays have been criticized for poor accuracy at low testosterone concentrations. Mass spectrometry (MS) has been proposed as the only reliable method for testosterone determination. The aim of this study was to compare a sensitive testosterone radioimmunoassay (RIA) with results from different MS. Methods. We compared testosterone concentrations determined by a sensitive testosterone RIA, lower limit of detection 0.03 nmol/L and limit of quantitation 0.1 nmol/L, with four tandem MS that were included in an international external quality assessment program for laboratory medicine. We also compared the morning concentrations of testosterone in girls and boys at different pubertal stages, using results from the RIA, with reported values determined by LC-MS/MS, developed for androgen determination in children. Results. The mean (SD), concentrations were similar between RIA and MS: 1.5 (0.3) and 1.4 (0.4) in the child/women range (0.8-2.6 nmol/L) and 16.0 (3.7) and 17.8 (4.5) nmol/L for the adult male range (10.1-30.0 nmol/L), respectively. The ratio between RIA and MS versus results from mean values of the four MS methods was 1.0 (0.18); 1.1 (0.18) for child/women concentrations and 0.9 (0.13) for male testosterone concentrations. Furthermore, compared to the pediatric reference values determined by LC-MS/MS, the sensitive testosterone RIA delivered similar testosterone values across the different pubertal stages. Conclusions. The comparison between different tandem MS methods and a sensitive testosterone RIA illustrates that there are immunoassays that deliver clinically useful information in prepubertal and pubertal children.

Background/Aim: The goal of estrogen replacement therapy (ERT) in girls with hypogonadism is to achieve the endocrine milieu similar to natural puberty, where transdermal administration is the most physiological route. The aim of the study was to evaluate guidelines for the induction of puberty with transdermal estradiol (E2) patches in a large outpatient setting. Methods: In a retrospective study, serum E2 levels from 18 clinics were analyzed at the Göteborg Pediatric Growth Research Center laboratory, as part of the initiation of ERT in girls with hypogonadism. Exclusion criteria were pubertas tarda and pubertal arrest. Eighty-eight observations (50 with Turner syndrome, TS) were included. Serum E2 levels were determined by extraction + radioimmunoassay (detection limit 4 pmol/l) and analyzed in relation to the dose of Evorel® (25 µg/24 h, containing 1.60 mg estradiol hemihydrate; Janssen-Cilag Pharmaceutica N.V., Beerse, Belgium). Results: There was a linear relationship between serum E2 and the weight-based dose, with r = 0.56, p < 0.0001 for all observations and r = 0.59, p < 0.0001 for the TS study group. Linear regression analysis for doses of 0.05-0.07 µg/kg resulted in serum levels of 17-23 pmol/l (TS 17-24 pmol/l) and doses of 0.08-0.12 µg/kg in 26-39 pmol/l (TS 27-39 pmol/l). Conclusions: For the initiation of ERT with nocturnally administered E2 patches, we recommend reduced starting doses of 0.05-0.07 µg/kg, with the goal of mimicking E2 levels during gonadarche. In older girls, when breast development is of high priority, the starting dose can still be 0.08-0.12 µg/kg.

OBJECTIVE:Different hypothalamic-pituitary-adrenal (HPA) axis function tests are used for diagnosing disease and evaluating suppressive effects of corticosteroid treatment. Our objectives were to evaluate sensitivity and precision of different HPA axis tests to be able to select one that combines good performance with good practicability, suitable for investigation of new corticosteroids in clinical trials.METHODS:In this descriptive, double-blind, parallel-group study, 60 healthy male volunteers were treated with once-daily morning doses of prednisolone for 2 weeks. The volunteers were randomized to 1 of 5 treatment groups (prednisolone 2.5, 5, 7.5, 10, or 15 mg). We compared the plasma-cortisol (p-cortisol) 24-hour average concentration (Cav) with morning (08:00 hours) p-cortisol, daytime p-cortisol Cav, and 24-hour urinary cortisol excretion. Adrenocorticotrophic hormone (ACTH) stimulation tests and the metyrapone test were also performed. Furthermore, we analyzed levels of serum dehydroepiandrosterone sulfate (s-DHEAS), insulin, and markers of bone turnover.RESULTS:Dose-related effects were shown, but the magnitude of effects and sensitivities varied greatly between the tests. P-cortisol measurements over the course of 24 hours were used as the reference method. Low- and standard-dose ACTH tests and morning s-DHEAS levels had similar sensitivity. Urinary cortisol excretion and the metyrapone stimulation test had low sensitivity. The effects of prednisolone on markers of bone turnover were, in general, less than those on the HPA axis. Only osteocalcin, procollagen Type 1 C-peptide and procollagen Type 3 N-peptide were significantly affected. Treatment with prednisolone was well tolerated.CONCLUSION:Changes in s-DHEAS and the low-dose ACTH test combine good sensitivity and precision for evaluation of the suppressive effect of exogenous corticosteroids on the HPA axis, and they are easy to perform.

AimsTo study the effect of exogenous i.m. glucagon on recovery from controlled insulin‐induced hypoglycaemia in patients with type 2 diabetes treated with the novel glucokinase activator AZD1656, in combination with metformin.MethodsThis was a single‐centre randomized, open, two‐way crossover phase I, automated glucose clamp (Biostator®; Life Science Instruments, Elkhart, MD, USA) study (NCT00817271) in eight patients (seven men and one woman, mean age 58.6 years, body mass index 28.1 kg/m2). All patients received a stable dose of metformin twice daily, ranging from 1000 to 2250 mg. A 2‐day titration phase commenced with 40 mg AZD1656 twice daily, escalating to 80 mg twice daily if tolerated. This was followed by a single dose of 80 or 160 mg AZD1656, administered on days 5 and 8 when metabolic studies were performed. After an overnight fast on days 5 and 8, controlled hypoglycaemia was induced using an exogenous i.v. infusion of insulin. Plasma glucose was lowered in a stepwise fashion over 3 h to attain a target nadir of 2.7 mmol/l. This was sustained for 30 min, at the end of which the hypoglycaemic clamp was released. In random sequence, patients either received an i.m. injection of 1 mg glucagon or were allowed to recover from hypoglycaemia by endogenous counter‐regulation. To avoid prolonged hypoglycaemia, a reverse glucose clamp was applied from 4 to 6 h post‐dose.ResultsThree patients received 40 mg AZD1656 twice daily and five patients 80 mg twice daily. Mean plasma glucose at 20 min after release of the hypoglycaemic clamp was significantly lower (3.1 ± 0.3 mmol/l) for AZD1656 alone than for AZD1656 + glucagon (4.9 ± 0.8 mmol/l; p < 0.001 between the groups). Catecholamine and cortisol responses were similar on the AZD1656 + glucagon and AZD alone study days. Growth hormone response was 18% lower for AZD1656 alone (p = 0.01), consistent with the effect of a pharmacological dose of glucagon on growth hormone secretion. No safety or tolerability concerns were observed during treatment with AZ1656.ConclusionsExogenous glucagon was effective as a rescue treatment for hypoglycaemia induced during treatment with AZD1656, given in combination with metformin in patients with type 2 diabetes.

Background/Aims: To study serum testosterone and estradiol in healthy boys in relation to growth during puberty up to peak height velocity (PHV). Methods: Growth velocity was analyzed through testosterone (n = 41) and 17β-estradiol (n = 37) 24-hour profiles in a dose-response model. Participants were 26 healthy boys admitted for short or tall stature or participating as healthy volunteers at the Queen Silvia Children's Hospital. Other inclusion criteria included the following: gestational age 37-42 weeks, birth weight and length >-2 standard deviation score (SDS) and prepubertal height and weight within ±3 SDS. Testosterone was measured using a modified radioimmunoassay (RIA) with a detection limit of 0.03 nmol/l. Estradiol was determined using an ultrasensitive extraction RIA with a detection limit 4 pmol/l. A sixth-grade polynomial was fitted to each child's growth data, giving growth velocity and age at PHV. Results: Growth velocity increased by 50% from prepubertal growth to PHV at a morning testosterone level of 3.1 nmol/l (95% confidence interval 2.4-4.2), EC50. The corresponding EC50 of 17β-estradiol was 6.5 pmol/l (3.2-13). Boys approaching PHV (<4% remaining) had morning testosterone levels >10 nmol/l and 17β-estradiol >9 pmol/l. Conclusion: Observed early puberty/initial mid puberty morning testosterone levels of 2.4-4.2 nmol/l are associated with a 50% increase in growth velocity from prepubertal growth to PHV in healthy boys.