The robustness of diagnostic tests for GH deficiency in adults

The history of an effective, specific and sensitive diagnostic test: the GHRH test in clinical practice

Growth hormone (GH) secretion is pulsatile, entropic, and nycthemeral and is mainly controlled by the hypothalamus through two neurohormones, the stimulating growth hormone releasing hormone (GHRH) and the inhibiting somatostatin. Shortly after its discovery and synthesis, GHRH was intensely investigated diagnostically to define GH secretion. The nascent enthusiasm for using GHRH as a single diagnostic tool to investigate GH deficiency (GHD) dropped down quickly due to a flawed reproducibility. The subsequent combinatory use of molecules implicated in GH secretion through inhibition of the somatostatinergic tone, such as arginine (ARG), or the synthesis of receptor-orphan pharmaceutical compounds capable of stimulating pituitary somatotrophs to release GH, such as the GH secretagogues (GHSs), improved the reproducibility of GH response to GHRH alone, thus gaining access into the clinical practice by means of different diagnostic approaches. This review will focus on the history of the GHRH test, with main emphasis on GHRH plus ARG as a dynamic testing for the diagnosis of GHD. Our attention will extend crosswise from studies aimed at validating GHRH-based tests for the clinical practice, to address main pitfall conditions capable of affecting per se GH secretion, such as obesity, hypothalamic damage, and ageing. The history of GHRH test has been progressively dismantled due to the cease of its production for business reasons, opening a gap in the diagnostic workup of patients with GHD. In the urgency to seek further robust, safe, and validated diagnostic tests or tools, we hope to stimulate attention on a so important peptide for the health of our patients suffering from pituitary diseases.

Once upon a time: the glucagon stimulation test in diagnosing adult GH deficiency

PURPOSE

The clinical features of adult GH deficiency (GHD) are nonspecific, and its diagnosis is established through GH stimulation testing, which is often complex, expensive, time-consuming and may be associated with adverse side effects. Moreover, diagnosing adult GHD can be challenging due to the influence of age, gender, and body mass index on GH peak at each test. The insulin tolerance test (ITT), GHRH + arginine test, glucagon stimulation test (GST), and, more recently, testing with macimorelin are all recognized as useful in diagnosing adult GHD. To date GST is still little used, but due to the unavailability of the GHRH all over the world and the high cost of macimorelin, in the next future it will probably become the most widely used test when ITT is contraindicated. The aim of the present review is to describe the current knowledge on GST.

METHODS

Narrative review.

RESULTS

In the last years several studies have suggested some changes in the original GST protocol and have questioned its diagnostic accuracy when the classic GH cut-point of 3 μg/L is used, suggesting to use a lower GH cut-point to improve its sensitivity and specificity in overweight/obese patients and in those with lower pretest GHD probability.

CONCLUSION

This document provides an update on the utility of GST, summarizes how to perform the test, shows which cut-points should be used in interpreting the results, and discusses its drawbacks and caveats referring to the most recent studies.

Trends of correlations between serum levels of growth hormone and insulin-like growth factor-I in general practice

Serum levels of growth hormone (GH) and insulin-like growth factor (IGF)-I are crucial in the diagnosis and management of GH-related diseases. However, these levels are affected by nutritional and metabolic status. To elucidate the correlations between GH and IGF-I in various conditions, a retrospective analysis was performed for adult patients in which GH levels were examined by general practitioners during the period from January 2019 to December 2021. Of 642 patients, 33 patients were diagnosed with acromegaly, 21 were diagnosed with GH deficiency (GHD), and 588 were diagnosed with non-GH-related diseases (NGRD). In contrast to the positive correlations found between the levels of GH and IGF-I in patients with acromegaly (R=0.50; P<0.001) and patients with GHD (R=0.39; P=0.08), a negative correlation was found in the NGRD group (R=-0.23; P<0.001). In that group, the results of multivariable analysis showed that GH levels were predominantly influenced by gender and body mass index (BMI), whereas IGF-I levels were modulated by albumin in addition to age and GH. Of note, in the NGRD group, there was an enhanced negative correlation between GH and IGF-I under conditions of BMI < 22 and albumin < 4.0 g/dL (R=-0.45; P<0.001), and the negative correlation between GH and IGF-I was reinforced by excluding patients with other pituitary diseases and patients taking oral steroids (R=-0.51; P<0.001 and R=-0.59; P<0.001, respectively). Collectively, the results indicate that attention should be given to the presence of a negative correlation between serum levels of GH and IGF-I, especially in lean and low-nutritious conditions.

Explaining Long COVID: A Pioneer Cross-Sectional Study Supporting the Endocrine Hypothesis

Context

In some patients, symptoms may persist after COVID-19, defined as long COVID. Its pathogenesis is still debated and many hypotheses have been raised.

Objective

Our primary objective was to evaluate the corticotroph and somatotroph functions of patients previously infected with SARS-CoV-2 and experiencing post-COVID-19 syndrome to detect any deficiencies that may explain long COVID.

Methods

A cross-sectional study was conducted including patients who had previously contracted SARS-CoV-2 with a postinfection period of 3 months or less to 15 months, divided into 2 groups. The first group (G1) comprised fully recovered patients, while the second group (G2) included patients experiencing long COVID. The primary outcome was the comparison of corticotroph and somatotroph functions.

Results

A total of 64 patients were divided into 2 groups, each consisting of 32 patients. G2 exhibited more frequently anterior pituitary deficits compared to G1 (P = .045): for the corticotroph axis (G1: 6.3% vs G2: 28.1%) and for the somatotroph axis (G1: 31.3% vs G2: 59.4%). Baseline cortisol level was significantly lower in G2 (G1: 13.37 µg/dL vs G2: 11.59 µg/dL) (P = .045). The peak cortisol level was also lower in G2 (G1: 23.60 µg/dL vs G2: 19.14 µg/dL) (P = .01). For the somatotroph axis, the insulin growth factor-1 level was lower in G2 (G1: 146.03 ng/mL vs G2: 132.25 ng/mL) (P = .369). The peak growth hormone level was also lower in G2 (G1: 4.82 ng/mL vs G2: 2.89 ng/mL) (P = .041).

Conclusion

The results showed that long COVID patients in our cohort were more likely to have anterior pituitary deficiencies. The endocrine hypothesis involving anterior pituitary insufficiency can be considered to explain long COVID.

Tolerable amounts of amino acids for human supplementation: summary and lessons from published peer-reviewed studies

Amino acid supplementation may be indicated to correct for insufficient amino acid intake in healthy individuals, and in specific physiological or pathophysiological situations. However, there is a concern to not supplement beyond the tolerable upper intake level (UL) by determining parameters of no-observed-adverse-effect level (NOAEL) or lowest-observed-adverse-effect level (LOAEL) for each amino acid. Since the NOAEL and LOAEL values are at least one order of magnitude different when comparing the values obtained in rats and humans, the aim of this review is to evaluate to what extent the amino acid UL measured in the rat model, when referenced to the dietary usual consumption (UC) and dietary requirement (RQ) for indispensable amino acids, may be used as an approximation of the UL in humans. This review then compares the ratios of the NOAEL or LOAEL over UC and RQ in the rat model with the same ratios calculated in humans for the nine amino acids (arginine, serine, glycine, histidine, leucine, lysine, methionine, phenylalanine, and tryptophan) for which this comparison can be done. From the calculations made, it appears that for these 9 amino acids, the calculated ratios for rats and humans, although rather different for several amino acids, remains for all of them in the same order of magnitude. For tryptophan, tyrosine, and valine, the ratios calculated in rats are markedly different according to the sex of animals, raising the view that it may be also the case in humans.

Development and Internal Validation of a Predictive Model for Adult GH Deficiency Prior to Stimulation Tests

BACKGROUND

The diagnosis of adult GH deficiency (GHD) relies on a reduced GH response to provocative tests. Their diagnostic accuracy, however, is not perfect, and a reliable estimation of pre-test GHD probability could be helpful for a better interpretation of their results.

METHODS

Eighty patients showing concordant GH response to two provocative tests, i.e. the insulin tolerance test and the GHRH + arginine test, were enrolled. Data on IGF-I values and on the presence/absence of other pituitary deficits were collected and integrated for the estimation of GHD probability prior to stimulation tests.

RESULTS

An independent statistically significant association with the diagnosis of GHD was found both for IGF-I SDS (OR 0.34, 95%-CI 0.18-0.65, p=0.001) and for the presence of other pituitary deficits (OR 6.55, 95%-CI 2.06-20.83, p=0.001). A low (<25%) pre-test GHD probability could be predicted when IGF-I SDS > +0.91 in the presence of other pituitary deficits or IGF-I SDS > -0.52 in the absence of other pituitary deficits. A high (>75%) pre-test GHD probability could be predicted when IGF-I SDS < -0.82 in the presence of other pituitary deficits or IGF-I SDS < -2.26 in the absence of other pituitary deficits.

CONCLUSION

This is the first study that proposes a quantitative estimation of GHD probability prior to stimulation tests. Our risk class stratification represents a simple tool that could be adopted for a Bayesian interpretation of stimulation test results, selecting patients who may benefit from a second stimulation test and possibly reducing the risk of wrong GHD diagnosis.

Growth hormone replacement in adults: Real-world data from two large studies in US and Europe

OBJECTIVE

This report describes the effectiveness and safety of growth hormone replacement in 3180 adult patients with growth hormone deficiency followed-up for 0.0-12.2 years in two completed, complementary, non-interventional, multicentre studies, NordiNet® International Outcome Study (IOS) (NCT00960128) and the American Norditropin® Studies: Web-Enabled Research (ANSWER) Program (NCT01009905).

DESIGN

In both studies, Norditropin® (somatropin; Novo Nordisk A/S, Denmark) was administered at the discretion of the treating physician and according to routine practice. We present data on baseline characteristics, growth hormone dose, safety data and change from baseline in waist circumference, body mass index and bioimpedance (NordiNet® IOS only).

RESULTS

Mean (SD) baseline characteristics (effectiveness analysis set) in NordiNet® IOS (n = 971) and ANSWER (n = 304): females, 45%; 69%; mean growth hormone dose (mg/day) (female, 0.338 [0.177]; male, 0.289 [0.157]); (female, 0.501 [0.313]; male, 0.505 [0.351]). Most patients had BMI ≥25 kg/m². Median (P10,P90) exposure (females, 3.5 [0.42,11.0]; 1.6 [3.2; 0.3,8.6]; males, 4.1 [0.33,10.8]; 2.3 [2.9; 0.0,7.5] years). Mean (SD) change from baseline for waist circumference (-0.46 [6.38] cm [n = 403], BMI (0.30 [3.30] kg/m² [n = 857]) and bioimpedance (-17.4 (59.19) ohm [n = 239]) were associated with growth hormone dose (waist/bioimpedance) and duration of follow-up (BMI/bioimpedance). No new safety signals were observed among patients in the full analysis set (NordiNet® IOS, n = 2321; ANSWER, n = 859).

CONCLUSIONS

Long-term growth hormone replacement is associated with an improvement in body composition. The accumulated data from >10 years of follow-up support the long-term effectiveness and safety of growth hormone replacement as prescribed in clinical practice.

Analysis of characteristics and outcomes by growth hormone treatment duration in adult patients in the Italian cohort of the Hypopituitary Control and Complications Study (HypoCCS)

PURPOSE

To examine differences in effects according to growth hormone (GH) treatment duration in adult GH-deficient patients.

METHODS

In the Italian cohort of the observational Hypopituitary Control and Complications Study, GH-treated adults with GH deficiency (GHD) were grouped by duration of treatment; ≤ 2 years (n = 451), > 2 to ≤ 6 years (n = 387) and > 6 years (n = 395). Between-group differences in demographics, medical history, physical characteristics, insulin-like growth factor-I standard deviation score (IGF-I SDS) and lipid profile at baseline, last study visit and changes from baseline to last study visit were assessed overall, for adult- and childhood-onset GHD and by gender using ANOVA for continuous variables and Chi-squared test for categorical variables.

RESULTS

At baseline, treatment duration groups did not differ significantly for age, gender, body mass index, GHD onset, IGF-I SDS, lipid profile, and quality of life. Mean initial GH dose did not differ significantly according to treatment duration group in any subgroup, except female patients, with highest mean dose seen in the longest duration group. In the longest duration group for patients overall, adult-onset patients and male patients, there were significant decreases in GH dose from baseline to last visit, and in total and low-density lipoprotein (LDL)-cholesterol concentrations. IGF-I SDS increased, to a greater extent, in the longest duration group for patients overall and female patients.

CONCLUSIONS

The results show that long-term GH treatment is associated with decreasing GH dose, increased IGF-I, decreased LDL-cholesterol and the presence of surrogate markers that help to give confidence in a diagnosis of GHD.

GHRH plus arginine and arginine administration evokes the same ratio of GH isoforms levels in young patients with Prader-Willi syndrome

Human GH is present in pituitary and circulation as several isoforms, the prevalent being 22kDa- and 20kDa-GH. Recently, we have demonstrated the preservation of a normal balance in GH isoforms after GH releasing hormone (GHRH) plus arginine (ARG) administration in adult patients with Prader-Willi syndrome (PWS), one of the most common causes of syndromic obesity, often associated with GH deficiency (GHD). Aim of the present study was to measure circulating levels of 22kDa- and 20kDa-GH in young PWS patients (n=24; F/M: 10/14; genotype UPD/DEL/met+: 11/11/2; age: 10.8±5.3years; BMI SDS: 2.0±2.0; GHD: 16/24; obesity: 12/24) after combined GHRH+ARG or ARG administration. The results were analysed subdividing the GHRH+ARG and ARG groups on the basis of PWS genotype, GHD status and obesity. Circulating levels of 22kDa- and 20kDa-GH were measured by a chemiluminescent or fluorescent method based on specific pairs of monoclonal antibodies. GHRH+ARG or ARG significantly stimulated the secretion of 22kDa-GH but not that of 20kDa-GH in all PWS patients. No significant GHRH+ARG- vs. ARG-induced changes in the ratios of 22kDa- to 20kDa-GH peaks were observed in all PWS patients, although 22kDa- or 20kDa-GH peaks were significantly higher in the GHRH+ARG than ARG group. When subdividing PWS patients in UPD vs. DEL, obese vs. non obese and GHD vs. non GHD subgroups, GH peaks were significantly higher in nonobese than obese patients and in non GHD than GHD patients administered with either GHRH+ARG or ARG test, apart from the comparisons in the DEL/UPD subgroups. Anyway, the ratios of peak levels of 22kDa- to 20kDa-GH were similar after GHRH+ARG vs. ARG in all subgroups investigated. In conclusion, this study shows that administration of two different pharmacological tests, i.e. ARG, capable of reducing hypothalamic somatostatinergic tone, and GHRH (+ARG), that directly acts at pituitary level on the somatotropic cell, evokes the same ratios of GH isoforms in young PWS patients, suggesting that the hypothalamic dysfunction in this genetic disorder does not alter the qualitative and quantitative composition of GH isoforms present in circulation.

The prevalence of growth hormone deficiency in survivors of subarachnoid haemorrhage: results from a large single centre study

OBJECTIVE

The variation in reported prevalence of growth hormone deficiency (GHD) post subarachnoid haemorrhage (SAH) is mainly due to methodological heterogeneity. We report on the prevalence of GHD in a large cohort of patients following SAH, when dynamic and confirmatory pituitary hormone testing methods are systematically employed.

DESIGN

In this cross-sectional study, pituitary function was assessed in 100 patients following SAH. Baseline pituitary hormonal profile measurement and glucagon stimulation testing (GST) was carried out in all patients. Isolated GHD was confirmed with an Arginine stimulation test and ACTH deficiency was confirmed with a short synacthen test.

RESULTS

The prevalence of hypopituitarism in our cohort was 19% and the prevalence of GHD was 14%. There was no association between GHD and the clinical or radiological severity of SAH at presentation, treatment modality, age, or occurrence of vasospasm. There were statistically significant differences in terms of Glasgow Outcome Scale (GOS; p = 0.03) between patients diagnosed with GHD and those without. Significant inverse correlations between GH peak on GST with body mass index (BMI) and waist hip ratio (WHR) was also noted (p < 0.0001 and p < 0.0001 respectively).

CONCLUSION

Using the current testing protocol, the prevalence of GHD detected in our cohort was 14%. It is unclear if the BMI and WHR difference observed is truly due to GHD or confounded by the endocrine tests used in this protocol. There is possibly an association between the development of GHD and worse GOS score. Routine endocrine screening of all SAH survivors with dynamic tests is time consuming and may subject many patients to unnecessary side-effects. Furthermore the degree of clinical benefit derived from growth hormone replacement in this patient group, remains unclear. Increased understanding of the most appropriate testing methodology in this patient group and more importantly which SAH survivors would derive most benefit from GHD screening is required.

The timing of administration of exogenous glucocorticoid affects 24hour growth hormone secretion in children

Exogenous glucocorticoids may suppress linear growth by affecting the diurnal secretory rhythm of GH.

OBJECTIVE

To assess whether the timing of exogenous glucocorticoid administration affects GH secretion in children.

DESIGN

Four girls and four boys aged 10.6 to 15.8 (mean 13.2) years with normal weight and height and pubertal stages I-IV were studied in an open randomized 2-period cross-over trial, with a 1-day un-in, and two 4-day periods of 5mg prednisolone in the morning or in the evening, respectively, separated by a 3-week washout period. At run-in and on the last day of each treatment period serum was collected every 20min for 24h for assessment of GH. Secondary analyses were serum levels of IGF-I and IGFBP-3 (measured every 8h), and IGFBP-1, insulin, and collagen markers PICP, PINP, ICTP and PIIINP (measured every 2h).

RESULTS

Evening prednisolone suppressed 24hour GH secretion (P=0.016), overnight GH secretion (P=0.023) and IGF-I (P=0.024) when compared to morning prednisolone, but not when compared to run-in. Evening prednisolone also increased nocturnal insulin levels as compared to run-in (P=0.010). Irrespective of time of day, prednisolone increased serum collagen markers PICP, PIINP, ICTP and PINP (all P<0.05).

CONCLUSIONS

Short-term prednisolone 5mg administered in the morning may alleviate nocturnal GH suppression as compared to evening administration. In analogy, growth rates are less affected by morning as compared to evening administration of exogenous glucocorticoids. In contrast, collagen markers and metabolic indices were not affected by the timing of prednisolone administration.

Anthropometric factors have significant influence on the outcome of the GHRH-arginine test: establishment of normative data for an automated immunoassay specifically measuring 22 kDa human growth hormone

CONTEXT

Adult growth hormone (GH) deficiency (GHD) is diagnosed by provocative testing of GH secretion.

OBJECTIVE

To improve the diagnostic accuracy of GH-releasing hormone (GHRH) plus arginine (GARG) testing, we evaluated the influence of age, BMI and sex and established normative data for an automatic immunoassay specifically measuring 22 kDa human GH.

DESIGN/SETTING

Prospective multicenter study.

PARTICIPANTS

Eighty-seven patients with hypothalamic-pituitary disease and 200 healthy controls. Patients were classified according to the number of pituitary hormone deficiencies (PHD). GHD was assumed when ≥2 PHD (in addition to GH) were present (n = 51); 36 patients with <2 PHD were considered GH sufficient (GHS). ROC analysis identified cutoffs with ≥95% specificity for GHD. Controls were prospectively stratified for sex, age and BMI.

INTERVENTIONS

All participants received GHRH and l-arginine.

MAIN OUTCOME MEASURES

GH was measured by immunoassay (iSYS, IDS).

RESULTS

In controls, multiple stepwise regression analysis showed that BMI (21%, P < 0.0001), sex (20%, P < 0.0001) and age (5%, P < 0.001), accounted for 46% of GH peak level variability during GARG. Comparison of peak GH during GARG (GHD vs GHS + controls) revealed an overall cutoff of 3.9 ng/mL (sensitivity 86%, specificity 95%). After adjustment for BMI and sex, optimal cutoffs (male vs female) were 6.5 vs 9.7 ng/mL in lean, 3.5 vs 8.5 ng/mL in overweight and 2.2 vs 4.4 ng/mL in obese subjects respectively.

CONCLUSION

BMI and sex account for most of the variability of peak GH levels during GARG. Consequently, diagnostic accuracy of the GARG test is significantly improved by use of adjusted cutoffs.

Effects of gender, body weight, and blood glucose dynamics on the growth hormone response to the glucagon stimulation test in patients with pituitary disease

OBJECTIVE

Body weight blunts the growth hormone (GH) response to provocative stimuli. The appropriate GH cut-off to confirm GH deficiency in obese and overweight patients undergoing the glucagon stimulation test (GST) has recently been questioned. We hypothesized that the peak GH would be inversely related to the nadir blood glucose (BG) after glucagon and that this may be a mechanism influencing peak GH in overweight patients. This retrospective study examined effects of gender, body weight, and BG dynamics on GH response to GST in patients evaluated in our Pituitary Center.

DESIGN

Adult patients who underwent GST from September 2009-2014 were included. Continuous variable comparisons were analyzed using the Mann-Whitney U-test and categorical data by Fisher's Exact Test. Spearman correlation was used to determine associations between continuous variables.

RESULTS

42 patients (N=28, 66.7% female) had sufficient data for analysis. Obese patients (N=26) had a reduced GH response, summarized as GH area under the curve (AUC) (p=0.03 vs. non-obese patients) and higher BG during GST, summarized as AUC (p<0.01 vs. non-obese patients). Obese women (N=19), in particular, stimulated lower (p=0.03 vs. non-obese women) and had a higher nadir BG (p=0.03 vs. non-obese women). While weight correlated with extent (rs=0.35; p=0.02) and timing (rs=0.31; p=0.05) of nadir BG reached, there was no significant correlation between BG dynamics and the GH response in the total population (N=42). Ten patients (7 with pan anterior hypopituitarism, defined as 3 anterior pituitary deficiencies) had a peak GH≤0.1ng/mL during GST. When these subjects with a negligible peak GH response were excluded from the analysis, weight was associated with GH AUC (rs=-0.45; p=0.01), peak GH response (rs=-0.42; p=0.02) and nadir BG (rs=0.48; p<0.01). Furthermore, the nadir BG achieved during GST was inversely related to GH AUC (rs=-0.38; p=0.03) and peak GH (rs=-0.37; p=0.04) such that patients (N=32) with higher nadir BG had lower peak GH in response to glucagon.

CONCLUSIONS

Obese patients, particularly women, do not respond as robustly to glucagon stimulation. These data suggest that there exists an altered BG profile during GST in obese individuals, and that a less robust hypoglycemic stimulus may contribute to an impaired GH response. We suggest measuring BG levels during glucagon stimulation testing to assist with clinical interpretation of GH dynamics. The diagnostic accuracy of the GST in patients with known disorders in glucose metabolism and those taking anti-diabetic medications deserves further study.