Human growth hormone measurement by means of a sensitive ELISA of whole blood spots on filter paper

Estimation of the reference values and decision limits for growth hormone in newborns using dried blood spots

OBJECTIVES

Severe deficiency of growth hormone (GHD) of the newborn is a rare but potentially life-threatening disease. GH measured during the first week of life, using dried blood spots (DBS), may offer several advantages. Aim of the study was to estimate the reference values for GH in newborns by a new analytical method using DBS.

METHODS

Using a new developed analytical method, GH was estimated from DBS of 1,036 healthy newborns attending the Neonatology Unit of Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico of Milan in the period July-October 2021. Reference values for GH deficiency were estimated by the Harrell-Davis bootstrap method, with 90 %CI calculated by the bias-corrected and accelerated bootstrap method.

RESULTS

All GH measurements required 33 analytical sessions (8 months) with a CV% for calibration curve slopes equal to 6.9 %. Intermediate precision evaluated by measurement of low (3 μg/L) and high (10 μg/L) quality controls was, respectively, 14 and 6.5 %. GH reference values, estimated at percentiles 1.0st, 2.5th and 5.0th, and their 90 %CI, were, respectively, 4.5 μg/L (90 %CI 3.8-5.1), 5.9 μg/L (90 %CI 5.4-6.4) and 7.0 μg/L (90 %CI 6.7-7.3). GH levels were not associated with sex, standard deviation scores, birth weight, gestational age, type of delivery or mother's variables (age, smoking habit, gestational diabetes).

CONCLUSIONS

Validation data suggest that this method can be used to measured GH in newborns using DBS. The reference values estimated in this study are in accordance with previous published works using ELISA and may help confirming the clinical suspicion of neonatal GHD.

Development and validation of a LC-MS/MS method for quantitation of recombinant human growth hormone in rat plasma and application to a pharmacokinetic study

Recombinant human growth hormone (rhGH) is a peptide comprising 191 amino acids, that is mainly used to promote the growth of children and plays an important antiaging role. In the present study, a simple and sensitive quantitation method for rhGH in rat plasma was established by LCMS/MS. After simple and rapid enzymatic digestion of the plasma sample, two suitable surrogate peptides (LFDNAMLR and FPTIPLSR) were selected for quantitative analysis. The results showed good linearity over calibration range 10-2000 ng/mL. The quality control (QC) accuracy ranged from -13.8 to 14.3%, and the accuracy of the lower limit of quantification (LLOQ) ranged from -12.9 to 19.0%. The intra-day and inter-day precision ranges for all QCs were 1.7-13.6% and 4.0-7.0%, respectively. The method was successfully applied to intravenous and subcutaneous pharmacokinetic studies in rats. In comparison with previously published methods, our method features simple sample preparation combined with a short sample processing time (3.5 h), wide linear range (10-2000 ng/mL), small plasma volume (35 μL), and LLOQ (10 ng/mL).

Diagnosis of severe growth hormone deficiency in the newborn

OBJECTIVE

Severe neonatal growth hormone deficiency (GHD) can cause recurrent hypoglycaemia. Early diagnosis is warranted. The aim of the study was to analyse the GH content in screening cards of 25 affected and 281 healthy newborns.

PATIENTS AND MEASUREMENTS

A total of 110 screening cards from ill newborns were sent to us for measuring GH content by a highly sensitive GH ELISA. Clinical information was obtainable in 61 cases. Severe GHD was defined by the presence of recurrent hypoglycaemia with a significant pituitary malformation or two additional pituitary hormone deficiencies. Screening cards from 281 healthy newborns (34.0-37.9 weeks) were prospectively analysed.

RESULTS

In 25 newborns (5 preterm), the definition of severe GHD was fulfilled based on recurrent hypoglycaemia in combination with malformation of the pituitary or midline structures in 21 cases and combined TSH and ACTH deficiency in four cases. The median GH concentration of those affected with severe GHD was 3.9 µg/L (range: 1.1-11.8), significantly below the previously reported reference range (P < .001). A GH concentration of 7 µg/L was confirmed as the cut-off for term newborns with the best accuracy (90.0% sensitivity and 98.7% specificity). The 95% reference range for healthy preterm newborns (n = 151) was 7.6-47.1 µg/L (median: 20.3 µg/L).

CONCLUSIONS

A GH content <7.0 µg/L in the newborn screening card confirms severe GHD with high accuracy. In preterm newborns, the lower limit of the reference interval was 0.6 µg/L higher than in term newborns. The newborn screening card is a valuable source for the very early diagnosis of GH deficiency.

Basal characteristics and first year responses to human growth hormone (GH) vary according to diagnostic criteria in children with non-acquired GH deficiency (naGHD): observations from a single center over a period of five decades

Background Children with non-acquired (na) growth hormone deficiency (GHD) diagnosed over decades in one center may provide perspective insight. Methods naGHD is divided into idiopathic GHD (IGHD), GHD of known cause (cGHD) and GHD neurosecretory dysfunction (NSD); time periods: <1988 (I); 1988-1997 (II); 1998-2007 (III); 2008-2015 (IV). Descriptive analyses were performed at diagnosis and during first year GH treatment. Results Patients (periods, N): I, 87; II, 141; III, 356; IV, 51. In cGHD (all), age, maximum GH, insulin-like growth factor-I (IGF-I), and insulin-like growth factor-binding protein-3 (IGFBP-3) (5.1 years, 3.6 μg/L, -5.3 standard deviation score [SDS], -3.7 SDS) were lower than in IGHD (all) (6.8 years 5.8 μg/L, -2.5 SDS, -1.0 SDS), but not height (-3.1 vs. -3.2 SDS). Characteristics of NSD were similar to that of IGHD. Patients with IGHD - not cGHD - diagnosed during 2008-2015 (IV) were the youngest with most severe GHD (maxGH, IGF-I, IGFBP-3), and first year height velocity (HV) and ∆ IGF-I (10.5 cm/year, 4.0 SDS) but not ∆ height SDS were the highest on recombinant human growth hormone (rhGH) (27 μg/kg/day). Conclusions Although during 1988-2007 patient characteristics were similar, the recently (>2008) stipulated more stringent diagnostic criteria - HV before testing, sex steroid priming, lower GH cut-off - have restricted diagnoses to more severe cases as they were observed before the rhGH era.

Growth hormone - past, present and future

Growth hormone (GH) research and its clinical application for the treatment of growth disorders span more than a century. During the first half of the 20th century, clinical observations and anatomical and biochemical studies formed the basis of the understanding of the structure of GH and its various metabolic effects in animals. The following period (1958-1985), during which pituitary-derived human GH was used, generated a wealth of information on the regulation and physiological role of GH - in conjunction with insulin-like growth factors (IGFs) - and its use in children with GH deficiency (GHD). The following era (1985 to present) of molecular genetics, recombinant technology and the generation of genetically modified biological systems has expanded our understanding of the regulation and role of the GH-IGF axis. Today, recombinant human GH is used for the treatment of GHD and various conditions of non-GHD short stature and catabolic states; however, safety concerns still accompany this therapeutic approach. In the future, new therapeutics based on various components of the GH-IGF axis might be developed to further improve the treatment of such disorders. In this Review, we describe the history of GH research and clinical use with a particular focus on disorders in childhood.

Comparative Analysis of Human Growth Hormone in Serum Using SPRi, Nano-SPRi and ELISA Assays

Sensitive and selective methods for the detection of human growth hormone (hGH) over a wide range of concentrations (high levels of 50-100 ng ml⁻¹ and minimum levels of 0.03 ng ml⁻¹) in circulating blood are essential as variable levels may indicate altered physiology. For example, growth disorders occurring in childhood can be diagnosed by measuring levels of hGH in blood. Also, the misuse of recombinant hGH in sports not only poses an ethical issue it also presents serious health threats to the abuser. One popular strategy for measuring hGH misuse, relies on the detection of the ratio of 22 kDa hGH to total hGH, as non-22 kDa endogenous levels drop after exogenous recombinant hGH (rhGH) administration.Surface plasmon resonance imaging (SPRi) is an analytical tool that allows direct (label-free) monitoring and visualization of biomolecular interactions by recording changes of the refractive index adjacent to the sensor surface in real time. In contrast, the most frequently used colorimetric method, enzyme-linked immunosorbent assay (ELISA) uses enzyme labeled detection antibodies to indirectly measure analyte concentration after the addition of a substrate that induces a color change. To increase detection sensitivity, amplified SPRi uses a sandwich assay format and near infrared quantum dots (QDs) to increase signal strength. After direct SPRi detection of recombinant rhGH in spiked human serum, the SPRi signal is amplified by the sequential injection of detection antibody coated with near-infrared QDs (Nano-SPRi). In this study, the diagnostic potential of direct and amplified SPRi was assessed for measuring rhGH spiked in human serum and compared directly with the capabilities of a commercially available ELISA kit.

Microcosmic mechanisms for protein incomplete release and stability of various amphiphilic mPEG-PLA microspheres

The microcosmic mechanisms of protein (recombinant human growth hormone, rhGH) incomplete release and stability from amphiphilic poly(monomethoxypolyethylene glycol-co-D,L-lactide) (mPEG-PLA, PELA) microspheres were investigated. PELA with different hydrophilicities (PELA-1, PELA-2, and PELA-3) based on various ratios of mPEG to PLA were employed to prepare microspheres exhibiting a narrow size distribution using a combined double emulsion and premix membrane emulsification method. The morphology, rhGH encapsulation efficiency, in vitro release profile, and rhGH stability of PELA microspheres during the release were characterized and compared in detail. It was found that increasing amounts of PLA enhanced the encapsulation efficiency of PELA microspheres but reduced both the release rate of rhGH and its stability. Contact angle, atomic force microscope (AFM), and quartz crystal microbalance with dissipation (QCM-D) techniques were first combined to elucidate the microcosmic mechanism of incomplete release by measuring the hydrophilicity of the PELA film and its interaction with rhGH. In addition, the pH change within the microsphere microenvironment was monitored by confocal laser scanning microscopy (CLSM) employing a pH-sensitive dye, which clarified the stability of rhGH during the release. These results suggested that PELA hydrophilicity played an important role in rhGH incomplete release and stability. Thus, the selection of suitable hydrophilic polymers with adequate PEG lengths is critical in the preparation of optimum protein drug sustained release systems. This present work is a first report elucidating the microcosmic mechanisms responsible for rhGH stability and its interaction with the microspheres. Importantly, this research demonstrated the application of promising new experimental methods in investigating the interaction between biomaterials and biomacromolecules, thus opening up a range of exciting potential applications in the biomedical field including drug delivery and tissue regeneration.

Rapid LC–MS/MS quantification of the major benzodiazepines and their metabolites on dried blood spots using a simple and cost-effective sample pretreatment

Background: Dried blood spots (DBS) sampling has gained popularity in the bioanalytical community as an alternative to conventional plasma sampling, as it provides numerous benefits in terms of sample collection and logistics. The aim of this work was to show that these advantages can be coupled with a simple and cost-effective sample pretreatment, with subsequent rapid LC–MS/MS analysis for quantitation of 15 benzodiazepines, six metabolites and three Z-drugs. For this purpose, a simplified offline procedure was developed that consisted of letting a 5-µl DBS infuse directly into 100 µl of MeOH, in a conventional LC vial. Results: The parameters related to the DBS pretreatment, such as extraction time or internal standard addition, were investigated and optimized, demonstrating that passive infusion in a regular LC vial was sufficient to quantitatively extract the analytes of interest. The method was validated according to international criteria in the therapeutic concentration ranges of the selected compounds. Conclusion: The presented strategy proved to be efficient for the rapid analysis of the selected drugs. Indeed, the offline sample preparation was reduced to a minimum, using a small amount of organic solvent and consumables, without affecting the accuracy of the method. Thus, this approach enables simple and rapid DBS analysis, even when using a non-DBS-dedicated autosampler, while lowering the costs and environmental impact.

Analysis of the GH content within archived dried blood spots of newborn screening cards from children diagnosed with growth hormone deficiency after the neonatal period

OBJECTIVE

It is unknown whether GH secretion of children with growth hormone deficiency (GHD) is already diminished at birth. We aimed to determine the GH content within archived dried blood spots of newborn screening cards from children diagnosed with GHD at childhood.

DESIGN

At our hospital, all children with the diagnosis of GHD and an actual age <10years were identified. For 16 patients (mean age, 7.4years; range, 1.0-9.7), screening cards were available. The archived dried blood from the first 48 to 96h of life was eluated in buffer of a highly sensitive hGH-ELISA to measure the GH content. Reference values were calculated based on 600 anonymous newborn screening cards of different ages.

RESULTS

Median GH content within the archived dried blood spots of the reference had declined by 30% during the first year and by further 35% during the next 8.5years of storage. After correction for time of storage, four out of the 16 archived dried blood spots of the GHD children contained low amounts of GH (≤5th percentile). Diminished GH secretion at birth was absent in isolated GHD, but associated with multiple pituitary hormone deficiency (MPHD) (P=0.0013), ectopic neurohypophysis (P=0.0013), lower GH test peak values (P=0.02) and higher weight at diagnosis (P=0.015).

CONCLUSIONS

Children with isolated GHD have normal GH secretory capacity during the first week of life while the majority of children with MPHD and pituitary malformation were GH deficient immediately after birth.

Harmonization of growth hormone measurements with different immunoassays by data adjustment

BACKGROUND

The aim of our study was to evaluate the between-assay variability of commercially available immunoassays for the measurement of human growth hormone (hGH). In addition, we asked whether the comparability of the diagnosis of childhood onset growth hormone deficiency could be improved by adjusting hGH results by statistical methods, such as linear regression, conversion factors, and quantile transformation.

METHODS

In archived sera from 312 children and adolescents (age: 17 days-17 years) hGH values between 0.01 and 16.5 ng/mL were determined by using the following immunoassays: AutoDELFIA (PerkinElmer), BC-IRMA (Beckman-Coulter), ELISA (Mediagnost), IMMULITE 2000 (Siemens), iSYS (IDS), Liaison (DiaSorin), UniCel DxI 800 Access (BeckmanCoulter) and "In house"-RIA (Tübingen).

RESULTS

The assays differed in median hGH concentrations by as much as 5.44 ng/mL (Immulite), and as little as 2.67 ng/mL (BC-IRMA). The mean difference between assays ranged from 0.35 to 2.71 ng/mL, whereas several samples displayed differences up to 11.4 ng/mL. The best correlation (r=0.992) was found between AutoDELFIA and Liasion, the lowest (r=0.864) was between an in-house RIA and iSYS. The between-assay CV (mean ± SD) of values within the cut-off range was 24.3% ± 7.4%, resulting in an assay-dependent diagnosis of growth hormone deficiency (GHD) in more than 27% of patients. Yet, adjustment of this data by linear regression or a conversion factor reduced the CV below 14%, and the ratio of assay-dependent diagnoses below 8%. Using quantile transformation, the CV and ratio were reduced to 11.4% and <1%, respectively.

CONCLUSIONS

hGH measurements using different assays vary significantly. Linear regression, conversion factors, or particularly quantile transformation are useful tools to improve comparability in the diagnostic procedure for the confirmation of GHD in childhood and adolescence.

Assessment of DBS technology for the detection of therapeutic antibodies

Background: Quantitating levels of therapeutic proteins in serum or plasma is critical for determining exposure levels and establishing pharmacokinetic parameters. Traditionally, whole blood is not used, mostly due to its inability to be frozen and potential issues with assay interference. To investigate the ability to reproducibly quantitate therapeutic antibodies present in dried blood spots (DBS) compared with a typical serum sample-based method, we used ELISA and electrochemiluminescence immunoassays to measure therapeutic drug levels present in DBS samples. Results: Measurements of antibody therapeutics in DBS were reproducible, yielding methods that are precise, accurate and met expected sensitivity requirements compared with plasma-based methods. Conclusions: DBS are a viable alternative to the use of conventional serum or plasma samples for quantitative therapeutic antibody measures.

Rational approach to the diagnosis of severe growth hormone deficiency in the newborn

CONTEXT

Severe congenital GH deficiency (GHD) of the newborn is a rare disease, which can cause life-threatening hypoglycemias beginning in the first week of life. Reviews and consensus papers on the diagnosis of GHD repeatedly state the lack of a practical evidence-based approach to the diagnosis of GHD in the newborn.

OBJECTIVE

Here we provide for the first time sound reference values and a diagnostic cutoff for the GH levels in newborns at the age between d 3 and 5.

DESIGN, SETTING, AND PATIENTS

GH was measured in the eluate from 314 filter papers of the newborn screening test performed in our university hospital by using a highly sensitive human GH-ELISA. Reference data are compared with measurements from nine newborns with very high likelihood of having severe GHD, and cutoffs for the diagnostic work-up are defined.

RESULTS

In the presence of clinical evidence, the diagnosis of neonatal GHD can be confirmed during the first week of life by a single randomly taken GH level less than 7 microg/liter with 100% sensitivity and 98% specificity on the basis of our assay method. GH content in newborn screening cards stored for almost 3 yr were not different from the content found in recently used screening cards indicating high immunological stability of GH over time. Therefore, the diagnostic approach can use stored screening cards. In addition, we observed a clear gender dichotomy in respect to GH, with healthy female newborns having significantly higher GH levels than males. Cigarette smoking during pregnancy was associated with higher, transient tachypnea of the newborn with lower GH levels.

CONCLUSIONS

We provide the first rational approach to the diagnosis of severe GHD in the newborn and evidence for gender dichotomy of the neonatal GH axis.