Diagnosis of growth hormone deficiency in childhood

Impact of the Choice of IGF-I Assay and Normative Dataset on the Diagnosis and Treatment of Growth Hormone Deficiency in Children

BACKGROUND

The analysis of insulin-like growth factor I (IGF-I) is an important tool for pediatricians in the diagnosis and treatment of growth hormone deficiency in children. However, significant differences exist in IGF-I assays and normative datasets, which can have important clinical consequences.

METHODS

IGF-I analyses were performed using the IDS-iSYS platform on 1,897 samples from pediatric patients (0.5-18 years old). Z-scores were calculated based on normative IGF-I data from Bidlingmaier et al. (SD-BM) [J Clin Endocrinol Metab. 2014 May; 99(5): 1712-21] and normative IGF-I data from the IGF-I harmonization program in the Netherlands (SD-NL). The differences in Z-scores were analyzed at relevant clinical decision points (-2 SD, +2 SD). These normative datasets were also compared to normative data reported by Elmlinger et al. [Clin Chem Lab Med. 2004; 42(6): 654-64].

RESULTS

The difference in Z-score between SD-BM and SD-NL was highest in males between 0 and 3 years old, exceeding 2 SD. Clinically relevant discordance between both Z-scores at -2 and +2 SD was found in 12.7% of all samples. The IGF-I levels at -2 and +2 SD reported in the normative dataset of Elmlinger et al. were up to 100% higher than the IGF-I levels reported by Bidlingmaier et al. or the Dutch harmonization program.

CONCLUSION

Pediatricians and laboratory specialists should be aware of relevant differences that can exist between IGF-I assays and normative data. Well-defined pediatric reference ranges for the IDS-iSYS platform are highly desirable.

Growth failure in focal dermal hypoplasia

Focal dermal hypoplasia (FDH) is a rare genetic disorder caused by mutations in the PORCN gene located on the X chromosome. Short stature was previously noted to be a common finding in FDH, however the etiology of this is unclear. The present study sought to elucidate specific causes for short stature by assessing growth charts, determining bone ages and auxologic measurements, examining laboratory data for the common causes of growth failure, assessing dietary intake, and performing a growth hormone stimulation test. Sixteen patients with FDH between the ages of 3 and 18 years of age consented to the study. While 11 out of 16 patients had short stature based on height less than 2 standard deviations below mid-parental target height percentile and bone age not suggestive of likely catch-up growth, only four had a BMI less than the 5th percentile for age. Laboratory studies did not support a gastrointestinal, allergy or autoimmune cause of growth failure. Three patients had results suggestive of possible growth hormone deficiency. Although short stature is a common feature in FDH, our data suggests that severe undernutrition is not common in this group and that there may be underlying treatable causes for this short stature in some patients.

Diagnostic Workup and Micronutrient Deficiencies in Children With Failure to Thrive Without Underlying Diseases

OBJECTIVES AND STUDY

Failure to thrive (FTT) is an interruption in the normal pattern of growth. We aimed to evaluate the clinical characteristics, underlying etiologies, diagnostic workup, and frequency of micronutrient deficiencies (MDs) in children with FTT.

METHODS

This retrospective study was done with 729 children (319 male, mean age 6.8 ± 5.5 years) with FTT (weight for age <3rd percentile) who had visited the Pediatric Gastroenterology outpatient clinic between 2011 and 2016. Children who had previously known chronic diseases, inadequate intake, or inadequate absorption were excluded. Acute malnutrition was considered if weight-for-age z-scores were below -2 and height-for-age z-scores were above -2, and chronic malnutrition was defined if height-for-age z-scores were below -2.

RESULTS

The malnutrition rate was 57.1% (acute: 37.8%, chronic: 19.3%). Of children, 98.7% had laboratory evaluation. We found that 1.1% of laboratory tests, 0.4% of imaging studies, 27% of endoscopic findings, and biopsy results led to a specific diagnosis, equating to a total of 1.3% of diagnostic workup leading to a diagnosis related to FTT. The causes of FTT were inadequate nutrition (61.4%), psychiatric and behavioral disorders (17.2%), endocrinologic disorders (9%), recurrent infections (6.4%), gastrointestinal diseases (1.9%), and cardiac disorders (0.1%). Vitamin A and D deficiencies were the most common MD.

CONCLUSION

We showed that the most common cause of FTT is "purely nutrition" FFT because of inadequate caloric intake, and extensive diagnostic workup is rarely helpful to reveal the etiology. These results implicate the importance of clinical evaluation and anthropometry to evaluate a child with FTT.

Endocrine Deficiency As a Function of Radiation Dose to the Hypothalamus and Pituitary in Pediatric and Young Adult Patients With Brain Tumors

PURPOSE

There are sparse data defining the dose response of radiation therapy (RT) to the hypothalamus and pituitary in pediatric and young adult patients with brain tumors. We examined the correlation between RT dose to these structures and development of endocrine dysfunction in this population.

MATERIALS AND METHODS

Dosimetric and clinical data were collected from children and young adults (< 26 years of age) with brain tumors treated with proton RT on three prospective studies (2003 to 2016). Deficiencies of growth hormone (GH), thyroid hormone, adrenocorticotropic hormone, and gonadotropins were determined clinically and serologically. Incidence of deficiency was estimated using the Kaplan-Meier method. Multivariate models were constructed accounting for radiation dose and age.

RESULTS

Of 222 patients in the study, 189 were evaluable by actuarial analysis, with a median follow-up of 4.4 years (range, 0.1 to 13.3 years), with 31 patients (14%) excluded from actuarial analysis for having baseline hormone deficiency and two patients (0.9%) because of lack of follow-up. One hundred thirty patients (68.8%) with medulloblastoma were treated with craniospinal irradiation (CSI) and boost; most of the remaining patients (n = 56) received involved field RT, most commonly for ependymoma (13.8%; n = 26) and low-grade glioma (7.4%; n = 14). The 4-year actuarial rate of any hormone deficiency, growth hormone, thyroid hormone, adrenocorticotropic hormone, and gonadotropin deficiencies were 48.8%, 37.4%, 20.5%, 6.9%, and 4.1%, respectively. Age at start of RT, time interval since treatment, and median dose to the combined hypothalamus and pituitary were correlated with increased incidence of deficiency.

CONCLUSION

Median hypothalamic and pituitary radiation dose, younger age, and longer follow-up time were associated with increased rates of endocrinopathy in children and young adults treated with radiotherapy for brain tumors.

The Use and Abuse of Human Growth Hormone in Sports

CONTEXT

Recombinant human growth hormone (rHGH) has become a target of abuse in the sporting world. Conversely, sports medicine clinicians may encounter athletes using rHGH to achieve normalcy in the context of growth hormone (GH) deficiency.

EVIDENCE ACQUISITION

Medline and PubMed databases were queried using the following keywords: GH, GH physiology, GH deficiency, acromegaly, GH athlete, GH sports, GH athletic performance, and GH deficiency concussion. Articles focusing on GH physiology, deficiency, excess, and its effects in both deficient and healthy patients were included.

STUDY DESIGN

Clinical review.

LEVEL OF EVIDENCE

Level 3.

RESULTS

GH is a naturally occurring hormone with important roles in human physiology. Patients with GH deficiency (GHD) present variably, and GHD has numerous etiologies. rHGH treatment has substantial therapeutic benefits for patients with GHD. The benefits of rHGH treatment in otherwise-healthy adults are uncertain. GH excess may cause health problems such as acromegaly. Professional, collegiate, and international sports leagues and associations have banned rHGH use to maintain athlete health, safety, and fair play. Athletes misusing GH may face prolonged suspensions from competition. Implementing GH abuse testing is challenging, but new methods, such as the biomarker testing procedure, are being finalized.

CONCLUSION

rHGH is not only an important therapeutic agent for GH-deficient patients but also a target of abuse in competitive athletics. Its benefits in a healthy, adult population are uncertain. A safe exercise and competition plan, developed with a physician knowledgeable of GH use, physiology, and abuse potential, should be of benefit to a longitudinal clinician-patient relationship.

Same Phenotype in Children with Growth Hormone Deficiency and Resistance

By definition, about 2.5% of children show a short stature due to several causes. Two clinical conditions are characterized by serum IGF-I low levels, idiopathic GH deficiency (IGHD), and GH insensitivity (GHI), and the phenotypic appearance of these patients may be very similar. We studied two children with short stature and similar phenotypes. The first case showed frontal bossing, doll face, acromicria, and truncal obesity, with a GH peak <0.05 ng/ml after stimuli and undetectable serum IGF-I levels. After PCR amplification of the whole GH1 gene, type IA idiopathic GHD was diagnosed. The second case had cranium hypoplasia, a large head, protruding forehead, saddle nose, underdeveloped mandible, and a micropenis. Basal GH levels were high (28.4 ng/ml) while serum IGF-I levels were low and unchangeable during the IGF-I generation test. Laron syndrome was confirmed after the molecular analysis of the GH receptor (GHR) gene. IGHD type IA and Laron syndrome is characterized by opposite circulating levels of GH, while both have reduced levels of IGF-I, with an overlapping clinical phenotype, lacking the effects of IGF-I on cartilage. These classical cases show the importance of differential diagnosis in children with severe short stature.

Vitamin D status in prepubertal children with isolated idiopathic growth hormone deficiency: effect of growth hormone therapy

Few studies, and with controversial results, analyzed vitamin D status in children before and after growth hormone (GH) treatment. Thus, we aimed to assess vitamin D status in prepubertal children with idiopathic growth hormone deficiency (GHD), and to evaluate the effect of GHD and GH treatment on vitamin D levels. Fifty prepubertal children with isolated GHD were compared with 50 controls. All were subjected to history, anthropometric assessment and measurement of 25 hydroxyvitamin D (25(OH)D), serum calcium, phosphorous, alkaline phosphatase and parathyroid hormone (PTH) at diagnosis and 1 year after GH therapy. Serum 25(OH)D levels <30 ng/mL and 20 ng/mL were defined as vitamin D insufficiency and deficiency, respectively. 25(OH)D was lower in cases than controls. Forty per cent of children with GHD were 25(OH)D insufficient and 44% deficient, while 16% were sufficient at baseline. There was a positive correlation between 25(OH)D and peak GH levels. Peak GH was a significant predictor of 25(OH)D levels. After 1 year of GH therapy, 25(OH)D increased (18.42±5.41 vs 34.5±10.1 ng/mL; P<0.001). Overall, 22% of cases remained insufficient and 24% deficient, with an increase in prevalence of children with normal levels (54%; P<0.001). 25(OH) correlated negatively with PTH (r=-0.71, P=0.01). In conclusion, hypovitaminosis D is prevalent in children with GHD and significantly improved 1 year after GH therapy. 25(OH)D should be assessed in children with GHD at diagnosis and during follow-up.

Pituitary imaging in 129 children with growth hormone deficiency: A spectrum of findings

Growth Hormone (GH) deficiency is the most common pituitary hormone deficiency in children. Magnetic Resonance Imaging (MRI) of the brain detects structural pituitary anomalies associated with GH deficiency. This retrospective hospital-based study was conducted at King Khalid University hospital (KKUH), Riyadh, Saudi Arabia, during the period (January 1995-June 2016). The available radiological, clinical and laboratory records of all children with confirmed GH deficiency by dynamic testing who had MRI brain were reviewed. A total of 129 patients were diagnosed with GH deficiency and had MRI brain performed. Isolated GH deficiency (IGHD) was diagnosed in 118 (91.5%) and multiple pituitary hormone deficiency (MPHD) in 11 (8.5%) patients. Most children with IGHD had normal MRI findings (n = 86/118), while 14/118 had hypoplasia of the anterior pituitary and 11/118 had aplasia of the anterior pituitary. Most of the children with MPHD (6/11) showed anterior pituitary hypoplasia or (3/11) aplasia and only 2/11 children with MPHD had normal MRI. In conclusion, our study showed a spectrum of MRI changes in children with GH deficiency.

Concomitant occurrence of Turner syndrome and growth hormone deficiency

Turner syndrome (TS) is a genetic disorder in phenotypic females that has characteristic physical features and presents as partial or complete absence of the second sex chromosome. Growth hormone deficiency (GHD) is a condition caused by insufficient release of growth hormone from the pituitary gland. The concomitant occurrence of TS and GHD is rare and has not yet been reported in Korea. Here we report 2 cases of TS and GHD. In case 1, GHD was initially diagnosed. Karyotyping was performed because of the presence of the typical phenotype and poor response to growth hormone therapy, which revealed 45,X/45,X+mar. The patient showed increased growth velocity after the growth hormone dose was increased. In case 2, a growth hormone provocation test and chromosomal analysis were performed simultaneously because of decreased growth velocity and the typical TS phenotype, which showed GHD and a mosaic karyotype of 45,X/46,XX. The patient showed spontaneous pubertal development. In female patients with short stature, it is important to perform a throughout physical examination and test for hormonal and chromosomal abnormalities because diagnostic accuracy is important for treatment and prognosis.

Challenges in the Diagnosis and Management of Growth Hormone Deficiency in India

In clinical practice, every year approximately 150,000 children are referred with short stature (SS) based on a cut-off of fifth percentile. The most important endocrine and treatable cause of SS is growth hormone deficiency (GHD). The lack of reliable data on the prevalence of GHD in India limits estimation of the magnitude of this problem. The diagnosis and treatment of GHD are hurdled with various challenges, restricting the availability of growth hormone (GH) therapy to only a very limited segment of the children in India. This review will firstly summarize the gaps and challenges in diagnosis and treatment of GHD based on literature analysis. Subsequently, it presents suggestions from the members at advisory board meetings to overcome these challenges. The advisory board suggested that early initiation of the therapy could better the chances of achieving final adult height within the normal range for the population. Education and awareness about growth disorders among parents, regular training for physicians, and more emphasis on using the Indian growth charts for growth monitoring would help improve the diagnosis and treatment of children with GHD. Availability of an easy-to-use therapy delivery system could also be beneficial in improving adherence and achieving satisfactory outcomes.

Revaluation of the clinical and metabolic behavior of children with isolated growth hormone deficiency during GH treatment according to newly proposed note 39 of the Italian Medicines Agency (AIFA)

PURPOSE

This study aimed at evaluating the clinical and metabolic behavior of children with isolated growth hormone (GH)-deficiency (GHD), grouped according to the new AIFA criteria for the appropriateness of use and reimbursement of GH treatment in children.

METHODS

The clinical and metabolic data of 310 prepubertal children (220 M, 90 F; mean age 10.8 years) grouped, according to new AIFA note 39, into Group A (No. 181 with a peak of GH <8 µg/l), Group B (No. 103 with a peak of GH ≥8 and <10 µg/l) and Group C (No. 26 with a peak of GH >10 µg/l) were retrospectively analyzed. Group A and B, diagnosed as having GHD, were treated with GH for at least 24 months, while Group C was analyzed only at baseline.

RESULTS

At baseline, Group A showed higher waist circumference than B (p = 0.031) and C (p = 0.041), while no difference in metabolic parameters was found between the three groups. After 12 and 24 months of treatment, Group B showed lower height velocity (p < 0.001 and p = 0.049, respectively) than Group A. As regards the metabolic parameters, both after 12 and 24 months of treatment, in Group B we found higher fasting glucose (p < 0.001 and p = 0.020), insulin (p = 0.002 and p = 0.011), Homa-β (p = 0.020 and p = 0.015) and Homa-IR (both p = 0.001) than Group A, with concomitant lower QUICKI (both p < 0.001) and HDL cholesterol (p = 0.020 and p = 0.011), without difference in other lipid parameters. The HbA1c levels, although always within the normal range, were found higher in Group B than Group A after 12 months (p = 0.015).

CONCLUSIONS

According to the new AIFA criteria, the reduction of GH cut-off for GHD diagnosis can be supported by auxological and metabolic data. The real benefits from GH therapy in children with higher stimulated GH levels at diagnosis remains to be better understand.

The effects of dietary protein and amino acids on skeletal metabolism

Dietary protein is required for optimal skeletal growth and maturation. Although Recommended Dietary Allowances (RDAs) exist for global dietary protein intake, the level and sources of dietary protein that are optimal for skeletal health over the life continuum have not been established. This is partly due to the difficulty in quantifying the effects of variable levels of a nutrient's intake over a lifetime as well as the complex nature of the relationships between dietary protein and calcium economy. Areas of current uncertainty include the precise source and amount of dietary protein required for optimal skeletal accretion and maintenance of skeletal mass, as well as the site-specific effects of dietary protein. The cellular and molecular mechanisms that underpin the actions of dietary protein on mineral metabolism and skeletal homeostasis remain unclear. This review attempts to summarize recent data bearing on these questions.

Isolated growth hormone deficiency (GHD) in childhood and adolescence: recent advances

The diagnosis of GH deficiency (GHD) in childhood is a multistep process involving clinical history, examination with detailed auxology, biochemical testing, and pituitary imaging, with an increasing contribution from genetics in patients with congenital GHD. Our increasing understanding of the factors involved in the development of somatotropes and the dynamic function of the somatotrope network may explain, at least in part, the development and progression of childhood GHD in different age groups. With respect to the genetic etiology of isolated GHD (IGHD), mutations in known genes such as those encoding GH (GH1), GHRH receptor (GHRHR), or transcription factors involved in pituitary development, are identified in a relatively small percentage of patients suggesting the involvement of other, yet unidentified, factors. Genome-wide association studies point toward an increasing number of genes involved in the control of growth, but their role in the etiology of IGHD remains unknown. Despite the many years of research in the area of GHD, there are still controversies on the etiology, diagnosis, and management of IGHD in children. Recent data suggest that childhood IGHD may have a wider impact on the health and neurodevelopment of children, but it is yet unknown to what extent treatment with recombinant human GH can reverse this effect. Finally, the safety of recombinant human GH is currently the subject of much debate and research, and it is clear that long-term controlled studies are needed to clarify the consequences of childhood IGHD and the long-term safety of its treatment.

Acute presentation of craniopharyngioma in children and adults in a Danish national cohort

We aimed to study the occurrence of acute-onset symptoms at initial presentation in a national Danish cohort of patients with childhood- or adult-onset craniopharyngioma, and to investigate potential risk factors for acute presentation. Medical records of 189 consecutive patients (39 children, 150 adults) presenting with craniopharyngioma during the period 1985-2004 were reviewed, and data regarding initial symptoms, neuroimaging results, vision and pituitary function were systematically collected. Acute symptoms preceding hospital admission were noted. Subgroup analyses were based on age, gender and calendar year period. Potential risk factors for acute presentation were analysed through uni- and multivariate analyses. Acute symptoms were reported in 24 (13%) patients. Acute visual symptoms, headache, nausea or vomiting were most frequently reported, and acute symptoms were more frequent among children (28%) than among adults (9%) (P < 0.01). There were no differences according to sex or calendar year period. Hydrocephalus was present in half of childhood cases and one-fifth of adult patients (P < 0.001). Intra-tumour haemorrhage was seen in two cases. Acute symptoms were more frequent among patients with tumours occupying the third ventricle (P < 0.01), radiologic signs of calcification (P < 0.05) or hydrocephalus (P < 0.01). In multivariate analysis, however, only childhood onset (P < 0.05) and calcification (P < 0.05) were independent risk factors for acute presentation. Craniopharyngioma presented with acute symptoms in 13% of patients. Childhood onset and radiologic signs of calcification were independent risk factors for acute presentation. Intra-tumour haemorrhage was rare.

Clonidine and glucagon stimulation for testing growth hormone secretion in children and adolescents: can we make it with fewer samples?

BACKGROUND

Our aim was to retrospectively evaluate the possibility to reduce the number of GH analyses during clonidine and glucagon tests without compromising accuracy.

SUBJECTS AND METHODS

Two hundred and forty-five tests were performed in a total of 188 children and adolescents with a mean age of 9.93 ± 2.88 yr in a single center during the last 5 yr.

RESULTS

Ninety-one out of 158 (57.59%) clonidine tests and 47/87 (54.02%) glucagon tests had at least one sample >10 μg/l (negative). For clonidine tests, not measuring GH at 30 min would have resulted in only one negative test missed (0.63% false positive result), whereas not measuring GH both at 0 and 30 min would have increased the false positive percentage to 2.53%. Ending clonidine tests at 90 min would have resulted in 7 negative tests missed (4.43% false positive results). For glucagon tests, more than half of the tests peaked at 120 min (56.32%). Skipping sampling at 0, 60 and 180 min provided a false positive rate of 5.75%.

CONCLUSIONS

For clonidine tests we can omit blood sampling at time points 0 and 30 min without significantly compromising accuracy.

The association between growth response to growth hormone and baseline body composition of children with growth hormone deficiency

OBJECTIVE

We wanted to examine the relationship between initial growth response to recombinant human Growth Hormone (rhGH) treatment and body composition in children with growth hormone deficiency (GHD).

DESIGN AND METHODS

Forty-two patients (21 boys and 21 girls) aged between 5.7-15.5 years (mean age: 10.8 ± 2.6 years) with isolated GHD. The auxological and laboratory data (GH and IGF-I levels) and results of bioelectrical impedance analyses were evaluated. Children with GHD were followed up for 12 months and categorized according to growth response to rhGH into good and poor responders (change in height of > 0.7 SDS or < 0.7 SDS over one year respectively). Mean doses of rhGH per kg of fat free mass (FFM) were calculated.

RESULTS

Forty-eight percent of patients showed a good growth response to rhGH therapy. At study entry, mean age, height SDS, weight SDS, serum IGF-1 SDS, IGFBP-3 SDS, growth velocity prior to rhGH therapy, GH after clonidine and l-dopa were similar in the two groups. At baseline, BMI SDS and waist-hip ratio were significantly higher in good responders (p = 0.02 and p = 0.006, respectively). Good responders had lower percentages of FFM (73.4 ± 8.9 vs. 83.1 ± 5.9) and total body water (TBW) (56.5 ± 5.3 vs. 63.1 ± 4.4), compared to poor responders (p < 0.05). There were significant correlations between changes in height SDS over one year and baseline body composition in children with GHD on rhGH treatment (r = -0.617 for percentage of FFM, r = -0.629 for percentage of TBW, p < 0.001). A correlation between BMI SDS, waist-hip ratio, mean rhGH dose per FFM and growth response was observed only in prepubertal subjects.

CONCLUSION

Baseline body composition data in children with GHD can be used to predict the growth response to rhGH treatment. A management strategy that involves titrating rhGH dose according to FFM as a means of optimizing the growth response to intervention requires further study.

Diagnostic value of provocative test by insulin combined with clonidine for growth hormone deficiency in children

OBJECTIVE

To evaluate the diagnostic value of provocative test by insulin combined with clonidine for growth hormone deficiency (GHD) during childhood.

METHODS

Eighty children underwent a provocative test with insulin(0.075U/Kg, intravenous) combined with clonidine (4μg/kg, orally). Among them, 40 children underwent clonidine provocative test, 40 children underwent insulin tolerance test (ITT) in another day.

FINDINGS

The specificity of ITT+clonidine test (74%, 88%) was remarkably higher than that of ITT (48%) or clonidine test (65%). ITT+clonidine test had a better accuracy (75%, 85%) than that of ITT (63%) or clonidine test (73%).

CONCLUSION

We conclude that the combined clonidine+insulin test is a feasible, reliable, convenient, time saving, and safe tool for evaluation of the growth hormone (GH) axes than the clonidine test or ITT.

Long-term skeletal consequences of childhood acute lymphoblastic leukemia in adult males: a cohort study

OBJECTIVE

Long-term health sequelae of childhood-onset acute lymphoblastic leukemia (ALL) remain largely unknown. Low bone mineral content (BMC) and bone mineral density (BMD) are recognized complications, but it is unknown whether these persist until adulthood. We evaluated skeletal characteristics and their association with ALL therapy in long-term male ALL survivors.

DESIGN

This cross-sectional cohort study included 49 long-term male ALL survivors and 55 age-matched healthy males.

METHODS

BMD and compression fractures were assessed by dual-energy X-ray absorptiometry; blood biochemistry was obtained for parameters of calcium homeostasis.

RESULTS

The ALL survivors (median age 29 years, range 25-38 years), assessed 10-38 years after ALL diagnosis, had lower lumbar spine (P<0.001), femoral neck (P<0.001), and whole-body (P=0.017) BMD than expected based on normative values. When compared with the controls (median age 30 years, range 24-36 years), the ALL survivors had lower lumbar spine BMC (P=0.014), lower whole-body BMC (P<0.001), and lower whole-body BMD (P<0.001), but the differences were partly explained by differences in height. Altogether, 20% of the ALL survivors had spinal compression fractures, but these were equally prevalent in the controls. Males diagnosed with ALL before age 5 years had significantly lower BMD values. Other recognized risk factors included untreated hypogonadism, vitamin D deficiency, hypophosphatemia, low IGF-binding protein-3, and low physical activity.

CONCLUSIONS

At young adulthood, long-term male ALL survivors have significantly reduced BMC and BMD and a high prevalence of spinal compression fractures. Careful follow-up and active treatment of the recognized risk factors are warranted.

Rapid development of sensitive, high-throughput, quantitative and highly selective mass spectrometric targeted immunoassays for clinically important proteins in human plasma and serum

OBJECTIVES

The aim of this study was to develop high-throughput, quantitative and highly selective mass spectrometric, targeted immunoassays for clinically important proteins in human plasma or serum.

DESIGN AND METHODS

The described method coupled mass spectrometric immunoassay (MSIA), a previously developed technique for immunoenrichment on a monolithic microcolumn activated with an anti-protein antibody and fixed in a pipette tip, to selected reaction monitoring (SRM) detection and accurate quantification of targeted peptides, including clinically relevant sequence or truncated variants.

RESULTS

In this report, we demonstrate the rapid development of MSIA-SRM assays for sixteen different target proteins spanning seven different clinically important areas (including neurological, Alzheimer's, cardiovascular, endocrine function, cancer and other diseases) and ranging in concentration from pg/mL to mg/mL. The reported MSIA-SRM assays demonstrated high sensitivity (within published clinical ranges), precision, robustness and high-throughput as well as specific detection of clinically relevant isoforms for many of the target proteins. Most of the assays were tested with bona-fide clinical samples. In addition, positive correlations, (R2 0.67-0.87, depending on the target peptide), were demonstrated for MSIA-SRM assay data with clinical analyzer measurements of parathyroid hormone (PTH) and insulin growth factor 1 (IGF1) in clinical sample cohorts.

CONCLUSIONS

We have presented a practical and scalable method for rapid development and deployment of MS-based SRM assays for clinically relevant proteins and measured levels of the target analytes in bona fide clinical samples. The method permits the specific quantification of individual protein isoforms and addresses the difficult problem of protein heterogeneity in clinical proteomics applications.