The effect of glucose dynamics on plasma copeptin levels upon glucagon, arginine, and macimorelin stimulation in healthy adults : Data from: Glucacop, Macicop, and CARGO study

The changing landscape in the evaluation of hypotonic polyuria in children and adolescents: the role of the new copeptin stimulation tests

Hypotonic polyuria, also known as the polyuria-polydipsia syndrome (PPS), caused by primary polydipsia (PP), arginine vasopressin deficiency (AVP-D or central diabetes insipidus), or uncommonly by AVP resistance (AVP-R), is diagnostically challenging due to overlapping symptoms and the need to conclusively diagnose or exclude AVP-D caused by serious organic lesions of the central nervous system. Diagnostic tests that stimulate AVP secretion by increasing plasma osmolality include the water deprivation test (WDT) and the hypertonic saline test (HST). The WDT, considered the gold standard for evaluating PPS in children, has suboptimal diagnostic accuracy, is burdensome, and requires hospitalization. The HST has been used rarely in children due to safety concerns and need for intensive monitoring. The finding that some anterior pituitary stimulating agents also stimulate the posterior pituitary, and the availability of a robust serum/plasma assay for copeptin as a reliable surrogate of AVP, has allowed development of nonosmotic, copeptin/AVP stimulation tests. In the present review, we focus on these new copeptin stimulation tests, which include single stimuli with intravenous (IV) arginine, IV insulin, intramuscular glucagon, oral levodopa, and double stimuli (IV arginine-insulin or AITT; IV arginine and oral Levodopa/carbidopa or ALD-ST), which we have previously shown to induce very robust copeptin secretion. Specifically, the ALD-ST differentiated AVP-D from PP in 20 children with high diagnostic accuracy at a cutoff stimulated copeptin of 9.3 pmol/L. We propose the utilization of the outpatient ALD-ST in the early stages of PPS evaluation in children, given its safety, cost-effectiveness, and limited side effects.

A post-hoc internal validation of arginine-stimulated copeptin cut-offs for diagnosing AVP deficiency (central diabetes insipidus)

BACKGROUND

Distinguishing arginine vasopressin (AVP) deficiency (central diabetes insipidus) from primary polydipsia is challenging. While hypertonic saline-stimulated copeptin testing provides the highest diagnostic accuracy, it is often restricted to specialised centres, requiring close monitoring and potentially causing patient discomfort. Initially, arginine-stimulated copeptin was proposed as a simpler alternative, but a head-to-head comparison study found it less precise than hypertonic saline stimulation. However, the same study identified two new high sensitivity and specificity cut-offs for arginine-stimulated copeptin, though these cut-offs have yet to be validated.

METHODS

This is a secondary post-hoc analysis of the initial prospective multicentre study, including adult patients with confirmed AVP deficiency or primary polydipsia. Participants underwent the arginine stimulation test, with plasma copeptin measured at baseline and 60- and 90 min after arginine infusion. The primary objective was to revisit the original study to internally validate the proposed arginine-stimulated copeptin cut-offs of > 5.2pmol/L (high specificity cut-off with > 90% specificity for primary polydipsia) and ≤ 3.0 pmol/L (high specificity cut-off with > 90% specificity for AVP deficiency).

FINDINGS

In total, 96 patients were included between May 2013 and June 2018: n = 38 [40%] with AVP deficiency and n = 58 [60%] with primary polydipsia. At 60 min after arginine infusion, a copeptin level ≤ 3.0 pmol/L showed a specificity of 95% (95% CI: 0.88-1.00) for AVP deficiency, while a copeptin level > 5.2 pmol/L demonstrated a specificity of 97% (95% CI: 0.92-1.00) for primary polydipsia. The ≤ 3.0 pmol/L cut-off accurately identified 71% (n = 27/38) of patients with AVP deficiency, and the > 5.2 pmol/L cut-off correctly identified 69% (n = 40/58) of patients with primary polydipsia.

INTERPRETATION

This analysis validates two new copeptin cut-offs of the arginine stimulation test to distinguish AVP deficiency from primary polydipsia: >5.2 pmol/L for high specificity in diagnosing primary polydipsia and ≤ 3.0 pmol/L for high specificity in diagnosing AVP deficiency. These thresholds might offer a practical initial alternative to hypertonic saline testing.

REGISTRATION

Clinicaltrials.gov (NCT00757276).

Relationship between plasma urea and copeptin in response to arginine stimulation in healthy adults, patients with vasopressin deficiency and primary polydipsia

BACKGROUND

Arginine infusion stimulates copeptin secretion, a surrogate marker of arginine vasopressin (AVP), thereby serving as a diagnostic test in the differential diagnosis of suspected AVP deficiency (AVP-D). Yet, the precise mechanism underlying the stimulatory effect of arginine on the vasopressinergic system remains elusive. Arginine plays a significant role in the urea cycle and increases the production of urea. An increase in plasma urea concentration raises blood osmolality, thereby possibly stimulating AVP release. We therefore hypothesized that the stimulatory effect of arginine on AVP may involve an increase in plasma urea levels.

METHODS

This analysis combined data from two prospective diagnostic studies. In total, 30 healthy adults (HA), 69 patients with AVP-D, and 89 patients with primary polydipsia (PP) underwent the arginine stimulation test. Infusion of arginine (L--arginine--hydrochloride 21%) at a dose of 0.5 g/kg body weight diluted in 500 mL of 0.9% normal saline was administered over 30 min. Blood was collected at baseline and 60, 90, and 120 min to analyze plasma copeptin and urea. The main objective was to investigate urea dynamics in response to arginine administration and its effect on copeptin release.

RESULTS

Plasma urea levels at baseline were comparable and increased 60 min after arginine infusion with a median (IQR) change of + 1.1 mmol/L (+ 0.8, + 1.5) in HA, + 1.4 mmol/L (+ 1.1, + 1.7) in patients with AVP-D and + 1.3 mmol/L (+ 0.9, + 1.5) in patients with PP. Concurrently, plasma copeptin levels substantially increased 60 min from baseline in HA (median change + 5.3 pmol/L (+ 3.2, + 8.8)) and in patients with PP (median change + 2.4 pmol/L (+ 1.2, + 3.8)), but remained stable in patients with AVP-D (median change + 0.3 pmol/L (+ 0.1, + 0.6)). Plasma urea and copeptin levels correlated the most in HA, with a Spearman's rho of 0.41 at baseline. Patients with AVP-D and PP showed only weak correlations of plasma urea and copeptin, with a correlation coefficient between 0.01 and 0.28.

CONCLUSION

We demonstrate a slight increase in plasma urea levels in response to arginine, but plasma urea and copeptin levels were weakly correlated. Based on these findings, the stimulatory effect of arginine on AVP cannot be explained primarily by increasing urea levels.

Impact Factors of Blood Copeptin Levels in Health and Disease States

OBJECTIVE

Copeptin, the C-terminal glycopeptide of provasopressin, is released into the circulation in an equimolar manner with arginine vasopressin (AVP) when fluid homeostasis changes or has somatic stress. Copeptin is considered a potential alternative to AVP due to its advantages in facilitating assays. Although there have been several studies and reviews that have focused on the marker potential of copeptin in diseases involving changes in AVP, studies on its characteristics and factors that may influence its secretion have not been reviewed before.

METHODS

We summarize the influencing factors associated with copeptin levels in healthy and disease states, show the changes in copeptin levels under different physiologic and pathophysiologic conditions, calculate the changes in copeptin levels under different physiologic and pathophysiologic conditions, and compare them according to the type of stimuli. We also report research advances in copeptin changes in the diagnosis and prognosis of endocrine-related diseases.

RESULTS

Males have higher copeptin levels. Decreased copeptin levels are mainly caused by reduced blood volume and some diseases (eg, obesity). Under normal physiologic conditions, the effects of stress, endocrine axis stimulation, and blood volume increase on copeptin levels gradually increase. Under severe disease conditions (eg, sepsis), copeptin would remain at consistently high levels under compound stimuli and these elevated levels are associated with a poor prognosis of the disease.

CONCLUSION

Summarizing the influencing factors of copeptin can help us better understand the biologic features of copeptin and the similarities and differences between AVP and copeptin.

Plasma oxytocin levels in response to glucagon in patients with arginine vasopressin deficiency (central diabetes insipidus) and healthy controls

PURPOSE

We recently demonstrated an additional oxytocin (OT) deficiency in patients with arginine vasopressin (AVP) deficiency (central diabetes insipidus) by using 3,4-methylenedioxy-methamphetamine (MDMA) as a novel provocation test. However, the implication of the MDMA provocation test in clinical practice might be challenging. Glucagon effectively stimulates vasopressinergic neurons with a strong increase in plasma copeptin. We therefore hypothesized that this provocation test might also stimulate OT.

METHODS

This is a predefined secondary analysis of a prospective double-blind, randomised, placebo-controlled cross-over trial involving ten patients with AVP deficiency and ten sex- and body-mass index-matched healthy participants at the University Hospital Basel, Switzerland. Each participant underwent the glucagon test (s.c. injection of 1 mg glucagon) and placebo test (s.c. injection of 0.9% normal saline). Plasma OT levels were measured at baseline, 60, 120 and 180 min after injection. The primary objective was to determine whether glucagon stimulates OT and whether OT levels differ between patients with AVP deficiency and healthy participants. The primary outcome (maximum change in OT within 180 min) was compared between groups and conditions using a linear mixed effects model.

RESULTS

In healthy participants, the median OT at baseline was 82.7 pg/ml [62.3-94.3] and slightly increased to a maximum of 93.3 pg/ml [87.2-121.1] after injection of glucagon, resulting in a change increase of 24.9 pg/ml [5.1-27.8]. Similarly, in patients with AVP deficiency, the median OT at baseline was 73.9 pg/ml [65.3-81.6] and slightly increased after glucagon injection to 114.9 pg/ml [70.9-140.9], resulting in a change increase of 36.8 pg/ml [-2.2 to 51.2]. The results from the mixed model showed no effect between glucagon compared to placebo on OT (difference: -0.5 pg/ml; 95%-CI [-25, 24]; p = 0.97) and no significant treatment-by-group interaction effect between patients compared to healthy participants (interaction: 28 pg/ml; 95%-CI [-7, 62]; p = 0.13).

CONCLUSION

We found no effect of glucagon on plasma OT levels and no difference between patients with AVP deficiency and healthy participants.

Determination of glucose cut-off points for optimal performance of glucagon stimulation test

Introduction

The glucagon stimulation test (GST) is widely used to assess growth hormone (GH) and cortisol secretion, nevertheless the precise mechanisms underpinning these hormonal responses remain unclear. We have endeavoured to explore the relationship between glucose and insulin fluctuations during GST and their impact on GH and cortisol secretion.

Subjects and methods

We retrospectively studied 139 subjects (mean age 35.5 ± 15.1 years, BMI 26.6 ± 6.61 kg/m²), including 62 individuals with a history of pituitary disease (27 with an intact adrenal axis) and 77 healthy controls. Standard dose intramuscular GST was performed in all subjects.

Results

Once BMI and age were excluded from multivariate model, the nadir of glucose concentration during GST was the sole variable associated with maximal GH secretion (ΔGH, p<0.0003), while neither glucose/insulin peak, nor Δglucose/Δinsulin concentrations contributed to ΔGH. 100% pass rate for GH secretion above 3 ng/ml or 1.07 ng/ml cut-offs was observed for glucose concentrations at, or below 60 mg/dl (3.33 mmol/l) (for Controls), or 62 mg/dl (3.44 mmol/l) (for Controls and patients with an intact adrenocortical axis). Such low glucose concentrations were obtained, however, only in about 30% of studied individuals. Conversely, cortisol secretion did not correlate with glucose or insulin fluctuations, suggesting alternative regulatory mechanisms.

Conclusions

This study reveals that glucose nadir below 3.33 mmol/l is the only biochemical biovariable linked with optimal GH secretion during GST, whereas mechanisms responsible for cortisol secretion remain unclear. We emphasize the importance of glucose monitoring during GST to validate GH stimulation and support clinical decisions in GH deficiency management.

The influence of insulin-induced hypoglycemia on copeptin concentrations

Plasma copeptin is a biomarker that reflects arginine vasopressin (AVP) secretion. In this study we measured copeptin during insulin tolerance test (ITT) in 65 patients referred to our department for evaluation of anterior pituitary function. Plasma for measurements of copeptin were collected at the start of the test and regurarly up to 120 minutes thereafter. Of 60 patients who developed significant hypoglycemia and were included in the analyses, 13 (22%) had corticotropic deficiency, 11 (18%) had thyreotropic deficiency, 33 (55%) had growth hormone deficiency and 4 (6%) had AVP deficieny (AVPD). Thirty-seven (62%) patients had at least one anterior pituitary deficiency. In patients without AVPD, median (range) copeptin increased from 4.5 pmol/L (1.3-33.0) to a maximum of 6.2 pmol/L (2.0-34.4; p<0.001). Baseline copeptin was similar in men and women, but maximal copeptin during ITT was higher in men. Copeptin concentrations were not affected by age, BMI, somatotropic, or corticotropic function. Copeptin concentrations were lower in patients with AVPD than patiets without AVPD, and in patients with thyrotropic deficiency, compared to patients with intact thyrotropic function, both at baseline and during ITT. In conclusion, copeptin increases significantly during insulin induced hypoglycemia but is of limited value in predicting anterior pituitary hormonal function.

Copeptin levels increase in response to both insulin-induced hypoglycemia and arginine but not to clonidine: data from GH-stimulation tests

Background

The diagnosis of the polyuria-polydipsia syndrome is challenging. Copeptin is a robust biomarker of arginine vasopressin (AVP) secretion. Arginine, which stimulates growth hormone (GH), has been shown also to stimulate copeptin secretion via unknown mechanisms.

Aim

The aim was to investigate copeptin levels in response to three different GH stimulation tests in patients suspected of GH deficiency.

Methods

In this cross-sectional study, we measured plasma copeptin levels at baseline and at 60, 105, and 150 min in patients undergoing a stimulation test for growth hormone deficiency with either arginine (n = 16), clonidine (n = 8) or the insulin tolerance test (ITT) (n = 10).

Results

In patients undergoing the arginine test, the mean age was 9 years, and 10 years for clonidine. The ITT was only performed in adult patients (>18 years) with a mean age of 49 years. Copeptin level increased significantly from baseline to 60 min after arginine (P <0.01) and ITT (P < 0.01). By contrast, copeptin level tended to decrease after clonidine stimulation (P = 0.14).

Conclusion

These data support that infusion of arginine increases plasma copeptin levels and reveal a comparable response after an ITT. We hypothesize that the underlying mechanism is abrogation of somatostatin-induced AVP suppression.