Insulin assay standardization: leading to measures of insulin sensitivity and secretion for practical clinical care

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

BACKGROUND

Numerous laboratory tests are used in the diagnosis and management of diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

APPROACH

An expert committee compiled evidence-based recommendations for laboratory analysis in screening, diagnosis, or monitoring of diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association for Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association.

CONTENT

Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (HbA1c) in the blood. Glycemic control is monitored by the people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring (CGM) devices and also by laboratory analysis of HbA1c. The potential roles of noninvasive glucose monitoring, genetic testing, and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed.

SUMMARY

The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Plasma proteomic signatures of a direct measure of insulin sensitivity in two population cohorts

AIMS/HYPOTHESIS

The euglycaemic-hyperinsulinaemic clamp (EIC) is the reference standard for the measurement of whole-body insulin sensitivity but is laborious and expensive to perform. We aimed to assess the incremental value of high-throughput plasma proteomic profiling in developing signatures correlating with the M value derived from the EIC.

METHODS

We measured 828 proteins in the fasting plasma of 966 participants from the Relationship between Insulin Sensitivity and Cardiovascular disease (RISC) study and 745 participants from the Uppsala Longitudinal Study of Adult Men (ULSAM) using a high-throughput proximity extension assay. We used the least absolute shrinkage and selection operator (LASSO) approach using clinical variables and protein measures as features. Models were tested within and across cohorts. Our primary model performance metric was the proportion of the M value variance explained (R2).

RESULTS

A standard LASSO model incorporating 53 proteins in addition to routinely available clinical variables increased the M value R2 from 0.237 (95% CI 0.178, 0.303) to 0.456 (0.372, 0.536) in RISC. A similar pattern was observed in ULSAM, in which the M value R2 increased from 0.443 (0.360, 0.530) to 0.632 (0.569, 0.698) with the addition of 61 proteins. Models trained in one cohort and tested in the other also demonstrated significant improvements in R2 despite differences in baseline cohort characteristics and clamp methodology (RISC to ULSAM: 0.491 [0.433, 0.539] for 51 proteins; ULSAM to RISC: 0.369 [0.331, 0.416] for 67 proteins). A randomised LASSO and stability selection algorithm selected only two proteins per cohort (three unique proteins), which improved R2 but to a lesser degree than in standard LASSO models: 0.352 (0.266, 0.439) in RISC and 0.495 (0.404, 0.585) in ULSAM. Reductions in improvements of R2 with randomised LASSO and stability selection were less marked in cross-cohort analyses (RISC to ULSAM R2 0.444 [0.391, 0.497]; ULSAM to RISC R2 0.348 [0.300, 0.396]). Models of proteins alone were as effective as models that included both clinical variables and proteins using either standard or randomised LASSO. The single most consistently selected protein across all analyses and models was IGF-binding protein 2.

CONCLUSIONS/INTERPRETATION

A plasma proteomic signature identified using a standard LASSO approach improves the cross-sectional estimation of the M value over routine clinical variables. However, a small subset of these proteins identified using a stability selection algorithm affords much of this improvement, especially when considering cross-cohort analyses. Our approach provides opportunities to improve the identification of insulin-resistant individuals at risk of insulin resistance-related adverse health consequences.

Changes in tear glucose and insulin concentrations following an oral glucose tolerance test

CLINICAL RELEVANCE

Tear glucose and insulin are responsible for the health of the ocular surface; thus, it is important for clinicians to detect the tear glucose and insulin using point-of-care methods.

AIM

To determine if changes in blood glucose and insulin levels following an oral glucose tolerance test are reflected in the tears and to test the association between gene expression and tear insulin and glucose.

METHODS

Twenty healthy young adults were enrolled. Basal tears and peripheral blood samples were collected to assess glucose and insulin using a point-of-care glucometer and ELISA assays in fasted subjects, and 1.5 and 3 h after an oral glucose challenge. Conjunctival impression cytology was collected to determine gene expression of insulin receptor (INSR) and glucose transporters (GLUT1 and GLUT4). Changes were examined using non-parametric one-way ANOVA. Spearman tests were conducted to examine associations between variables.

RESULTS

Glucose and insulin levels increased 1.5 h after oral glucose in both blood (P < 0.001) and tears (P < 0.049) and returned to near baseline values after 3 h. There was a positive correlation between glucose levels in the blood and tears (rho = 0.57, P < 0.001), but not between blood and tear insulin levels (P = 0.18). Glucose and insulin levels in tears were correlated (rho = 0.32, P = 0.048). Tear glucose concentration at 1.5 h after oral glucose was associated with INSR expression (rho = 0.49, P = 0.03), and there was a trend with GLUT1 (P = 0.06) but not GLUT4.

CONCLUSION

Tear glucose reflected blood glucose levels but this correspondence was not observed for insulin. Further studies are required to determine the role of glucose and insulin on the ocular surface in both health and diabetes.

Development of a Web App to Convert Blood Insulin Concentrations among Various Immunoassays Used in Horses

The measurement of the blood insulin concentration, and comparison to cut-offs, is essential in diagnosing insulin dysregulation, a common equine endocrinopathy. However, different insulin assays provide disparate results. We aimed to ease comparison between assays by compiling original and published data into a web app to convert insulin measurements from one assay to another. Data were available for ADVIA Centaur insulin chemiluminescent immunoassay (CLIA), Beckman Coulter insulin radioimmunoassay (RIA), Immulite 1000 CLIA, Immulite 2000 CLIA, Immulite 2000 XPi CLIA, Mercodia equine insulin enzyme-linked immunosorbent assay (ELISA), and Millipore porcine insulin RIA. Linear models were fitted for 13 assay pairs using non-decreasing splines, and integrated into this app. Assay comparisons including data from several studies showed a lower performance. This indicates technical variation between laboratories, which has not been described before, but is relevant when diagnostic measurements and cut-offs are provided by different laboratories. Nevertheless, the models' overall high performance (median r2 = 0.94; range 0.57-1.00) supports their use to interpret results from diagnostic insulin measurements when the reference assay is unavailable, and to compare values obtained from different assays.

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

BACKGROUND

Numerous laboratory tests are used in the diagnosis and management of diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

APPROACH

An expert committee compiled evidence-based recommendations for laboratory analysis in screening, diagnosis, or monitoring of diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association of Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association.

CONTENT

Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (Hb A1c) in the blood. Glycemic control is monitored by the people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring (CGM) devices and also by laboratory analysis of Hb A1c. The potential roles of noninvasive glucose monitoring, genetic testing, and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed.

SUMMARY

The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Identification of Metabolism-Related Proteins as Biomarkers of Insulin Resistance and Potential Mechanisms of m6A Modification

BACKGROUND

Insulin resistance (IR) is a major contributing factor to the pathogenesis of metabolic syndrome and type 2 diabetes mellitus (T2D). Adipocyte metabolism is known to play a crucial role in IR. Therefore, the aims of this study were to identify metabolism-related proteins that could be used as potential biomarkers of IR and to investigate the role of N⁶-methyladenosine (m⁶A) modification in the pathogenesis of this condition.

METHODS

RNA-seq data on human adipose tissue were retrieved from the Gene Expression Omnibus database. The differentially expressed genes of metabolism-related proteins (MP-DEGs) were screened using protein annotation databases. Biological function and pathway annotations of the MP-DEGs were performed through Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses. Key MP-DEGs were screened, and a protein-protein interaction (PPI) network was constructed using STRING, Cytoscape, MCODE, and CytoHubba. LASSO regression analysis was used to select primary hub genes, and their clinical performance was assessed using receiver operating characteristic (ROC) curves. The expression of key MP-DEGs and their relationship with m⁶A modification were further verified in adipose tissue samples collected from healthy individuals and patients with IR.

RESULTS

In total, 69 MP-DEGs were screened and annotated to be enriched in pathways related to hormone metabolism, low-density lipoprotein particle and carboxylic acid transmembrane transporter activity, insulin signaling, and AMPK signaling. The MP-DEG PPI network comprised 69 nodes and 72 edges, from which 10 hub genes (FASN, GCK, FGR, FBP1, GYS2, PNPLA3, MOGAT1, SLC27A2, PNPLA3, and ELOVL6) were identified. FASN was chosen as the key gene because it had the highest maximal clique centrality (MCC) score. GCK, FBP1, and FGR were selected as primary genes by LASSO analysis. According to the ROC curves, GCK, FBP1, FGR, and FASN could be used as potential biomarkers to detect IR with good sensitivity and accuracy (AUC = 0.80, 95% CI: 0.67-0.94; AUC = 0.86, 95% CI: 0.74-0.94; AUC = 0.83, 95% CI: 0.64-0.92; AUC = 0.78, 95% CI: 0.64-0.92). The expression of FASN, GCK, FBP1, and FGR was significantly correlated with that of IGF2BP3, FTO, EIF3A, WTAP, METTL16, and LRPPRC (p < 0.05). In validation clinical samples, the FASN was moderately effective for detecting IR (AUC = 0.78, 95% CI: 0.69-0.80), and its expression was positively correlated with the methylation levels of FASN (r = 0.359, p = 0.001).

CONCLUSION

Metabolism-related proteins play critical roles in IR. Moreover, FASN and GCK are potential biomarkers of IR and may be involved in the development of T2D via their m⁶A modification. These findings offer reliable biomarkers for the early detection of T2D and promising therapeutic targets.

Application of serum pools in insulin harmonization: Commutability and stability

BACKGROUND

Recalibration using serum pools assigned by higher-order reference methods had been demonstrated to be effective in improving the agreement among insulin immunoassays. To promote the application of serum pools in insulin harmonization, this study analyzed serum pools' commutability between insulin immunoassays, and their short- and long-term stability at different temperatures. The agreement between commonly used immunoassays was also evaluated.

METHODS

Insulin in 69 individual serum samples, 10 serum pools, and three EQA samples (lyophilized powder of serum pools) were detected by six widely used immunoassays. The commutability of serum pools and EQA samples was evaluated according to the IFCC-recommended approach. Serum pools' stability at different temperatures was investigated by placing them at various temperatures for varying lengths of time. Individual serum samples' results were analyzed using the Bland-Altman and Passing and Bablok regression analyses.

RESULTS

Serum pools were commutable among most assays, the EQA samples-lyophilized serum pools-were non-commutable among most assays. Serum pools can be stably stored at -20°C and -80°C for at least one year, but can only be stably stored at room temperature for twenty-four hours. Significant relative differences were observed among assays. Recalibration using serum pools can only improve the assays' agreement at middle and high insulin levels, but not at low levels.

CONCLUSIONS

Serum pools were commutable and stable for insulin measurement and can be used in insulin harmonization. The existing EQA materials were non-commutable between most assays, and other EQA materials, such as serum pools, should be studied.

Lipoprotein Insulin Resistance Index: A Simple, Accurate Method for Assessing Insulin Resistance in South Asians

Context

Identification of insulin resistance (IR) in South Asians, who are at a higher risk for type 2 diabetes, is important. Lack of standardization of insulin assays limits the clinical use of insulin-based surrogate indices. The lipoprotein insulin resistance index (LP-IR), a metabolomic marker, reflects the lipoprotein abnormalities observed in IR. The reliability of the LP-IR index in South Asians is unknown.

Objective

We evaluated the predictive accuracy of LP-IR compared with other IR surrogate indices in South Asians.

Methods

In a cross-sectional study (n = 55), we used calibration model analysis to assess the ability of the LP-IR score and other simple surrogate indices (Homeostatic Model Assessment of Insulin Resistance, Quantitative insulin sensitivity check index, Adipose insulin resistance index, and Matsuda Index) to predict insulin sensitivity (S_I) derived from the reference frequently sampled intravenous glucose tolerance test. LP-IR index was derived from lipoprotein particle concentrations and sizes measured by nuclear magnetic resonance spectroscopy. Predictive accuracy was determined by root mean squared error (RMSE) of prediction and leave-one-out cross-validation type RMSE of prediction (CVPE). The optimal cut-off of the LP-IR index was determined by the area under the receiver operating characteristic curve (AUROC) and the Youden index.

Results

The simple surrogate indices showed moderate correlations with S_I (r = 0.53-0.69, P < .0001). CVPE and RMSE were not different in any of the surrogate indices when compared with LP-IR. The AUROC was 0.77 (95% CI 0.64-0.89). The optimal cut-off for IR in South Asians was LP-IR >48 (sensitivity: 75%, specificity: 70%).

Conclusion

The LP-IR index is a simple, accurate, and clinically useful test to assess IR in South Asians.

Acanthosis nigricans in the pediatric population: a narrative review of the current approach to management in primary care

Objective

This narrative review aims to provide readers with a comprehensive overview of the current literature of acanthosis nigricans (AN) in the pediatric and adolescent population, including best practices for identifying the condition, with a focus on the recommended management in the primary care setting to enable early and enhanced intervention.

Background

AN is frequently seen in obese and overweight children and adolescents. Current research suggests an association with insulin resistance, type 2 diabetes mellitus, and obesity, and often primary care physicians are the first point of contact for individuals with this dermatologic condition. However, identifying the condition at an early stage may be difficult.

Methods

We identified case and cross-sectional studies, clinical trials, and literature reviews of pediatric AN for ages 0 to 18 years in the United States and internationally. We considered publications for background from before the year 2000 and publications for approach to management from after the year 2000.

Conclusions

AN in the pediatric population can be a harbinger for underlying metabolic syndrome and insulin resistance. A thorough investigation and appropriate screening of children at risk, with a focus on early identification of the dermatologic condition and its associated comorbidities in the primary care setting, and early treatment is recommended to prevent long term consequences and decrease the risk of cardiovascular complications.

A Glucose-Only Model to Extract Physiological Information from Postprandial Glucose Profiles in Subjects with Normal Glucose Tolerance

BACKGROUND

Current mathematical models of postprandial glucose metabolism in people with normal and impaired glucose tolerance rely on insulin measurements and are therefore not applicable in clinical practice. This research aims to develop a model that only requires glucose data for parameter estimation while also providing useful information on insulin sensitivity, insulin dynamics and the meal-related glucose appearance (GA).

METHODS

The proposed glucose-only model (GOM) is based on the oral minimal model (OMM) of glucose dynamics and substitutes the insulin dynamics with a novel function dependant on glucose levels and GA. A Bayesian method and glucose data from 22 subjects with normal glucose tolerance are utilised for parameter estimation. To validate the results of the GOM, a comparison to the results of the OMM, obtained by using glucose and insulin data from the same subjects is carried out.

RESULTS

The proposed GOM describes the glucose dynamics with comparable precision to the OMM with an RMSE of 5.1 ± 2.3 mg/dL and 5.3 ± 2.4 mg/dL, respectively and contains a parameter that is significantly correlated to the insulin sensitivity estimated by the OMM (r = 0.7) Furthermore, the dynamic properties of the time profiles of GA and insulin dynamics inferred by the GOM show high similarity to the corresponding results of the OMM.

CONCLUSIONS

The proposed GOM can be used to extract useful physiological information on glucose metabolism in subjects with normal glucose tolerance. The model can be further developed for clinical applications to patients with impaired glucose tolerance under the use of continuous glucose monitoring data.

Multiplexed quantification of insulin and C-peptide by LC-MS/MS without the use of antibodies

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Simultaneous quantification of insulin and C-peptide without antibodies.

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Proteolysis with Glu-C permits sensitive and precise measurements.

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Calibration with certified reference material provides traceability.

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Relatively large bias when compared with a commercially available immunoassay.

Introduction

The measurement of insulin and C-peptide provides a valuable tool for the clinical evaluation of hypoglycemia. In research, these biomarkers are used together to better understand hyperinsulinemia, hepatic insulin clearance, and beta cell function. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is an attractive approach for the analysis of insulin and C-peptide because the platform is specific, can avoid certain limitations of immunoassays, and can be multiplexed. Previously described LC-MS/MS methods for the simultaneous quantification of insulin and C-peptide measure the intact analytes and most have relied on immunoaffinity enrichment. These approaches can be limited in terms of sensitivity and interference from auto-antibodies, respectively. We have developed a novel method that does not require antibodies and uses proteolytic digestion to yield readily ionizable proteotypic peptides that enables the sensitive, specific, and simultaneous quantitation of insulin and C-peptide.

Methods

Serum samples were precipitated with acetonitrile. Analytes were enriched using solid phase extraction and then digested with endoproteinase Glu-C. Surrogate peptides for insulin and C-peptide were analyzed using targeted LC-MS/MS.

Results

Inter-day imprecision was below 20 %CV and linearity was observed down to the lower limit of quantitation for both analytes (insulin = 0.09 ng/mL, C-peptide = 0.06 ng/mL). Comparison to a commercially available insulin immunoassay (Beckman Coulter UniCel DxI 600 Access) revealed a 30% bias between methods.

Conclusion

A novel LC-MS/MS method for the simultaneous analysis of insulin and C-peptide using Glu-C digestion was developed and evaluated. A detailed standard operating procedure is provided to help facilitate implementation in other laboratories.

Current Status of Serum Insulin and C-Peptide Measurement in Clinical Laboratories: Experience from 94 Laboratories in China

Background

Accurate measurements of serum insulin and C-peptide are needed for the therapy and classification of diabetes. This study investigated the status of serum insulin and C-peptide measurements in China by analyzing the results of five pooled serum samples measured in 94 laboratories.

Methods

Patient serum samples were pooled into five groups according to insulin and C-peptide concentrations and measured in 94 laboratories using different measurement systems. The inter- and intra-laboratory %CV as well as inter- and intra-measurement system %CV were calculated to assess the status of insulin and C-peptide measurements. To verify whether the disagreement between laboratories was due to different calibrators, as reported in previous studies, one low-level and one high-level sample extracted from the five pooled serum samples were used to recalibrate clinical measurement systems.

Results

The mean intra-laboratory, intra-measurement system, inter-laboratory, and inter-measurement system %CVs were 2.7%, 4.8%, 21.8%, and 22.4%, respectively, for insulin and 2.3%, 6.7%, 16.4%, and 24.5%, respectively, for C-peptide. The inter- and intra-laboratory %CVs for insulin decreased with increasing concentration. After recalibration with low- and high-level samples, the mean inter-measurement %CV decreased from 22.4% to 17.2% for insulin and from 24.5% to 5.7% for C-peptide.

Conclusions

The intra-laboratory and intra-measurement system imprecision values are satisfactory for serum insulin and C-peptide measurements. However, the results from laboratories using different measurement systems were not comparable, and there is still much work needed to achieve the standardization or harmonization of serum insulin and C-peptide measurements.

Intact Fasting Insulin Identifies Nonalcoholic Fatty Liver Disease in Patients Without Diabetes

CONTEXT

Patients with nonalcoholic fatty liver disease (NAFLD) are characterized by insulin resistance and hyperinsulinism. However, insulin resistance measurements have not been shown to be good diagnostic tools to predict NAFLD in prior studies.

OBJECTIVE

We aimed to assess a newly validated method to measure intact molecules of insulin by mass spectrometry to predict NAFLD.

METHODS

Patients underwent a 2-hour oral glucose tolerance test (OGTT), a liver magnetic resonance spectroscopy (1H-MRS), and a percutaneous liver biopsy if they had a diagnosis of NAFLD. Mass spectrometry was used to measure intact molecules of insulin and C-peptide.

RESULTS

A total of 180 patients were recruited (67% male; 52 ± 11 years of age; body mass index [BMI] 33.2 ± 5.7 kg/m2; 46% with diabetes and 65% with NAFLD). Intact fasting insulin was higher in patients with NAFLD, irrespective of diabetes status. Patients with NAFLD without diabetes showed ~4-fold increase in insulin secretion during the OGTT compared with all other subgroups (P = 0.008). Fasting intact insulin measurements predicted NAFLD in patients without diabetes (area under the receiver operating characteristic curve [AUC] of 0.90 [0.84-0.96]). This was significantly better than measuring insulin by radioimmunoassay (AUC 0.80 [0.71-0.89]; P = 0.007). Intact fasting insulin was better than other clinical variables (eg, aspartate transaminase, triglycerides, high-density lipoprotein, glucose, HbA1c, and BMI) to predict NAFLD. When combined with alanine transaminase (ALT) (intact insulin × ALT), it detected NAFLD with AUC 0.94 (0.89-0.99) and positive and negative predictive values of 93% and 88%, respectively. This newly described approach was significantly better than previously validated noninvasive scores such as NAFLD-LFS (P = 0.009), HSI (P < 0.001), and TyG index (P = 0.039).

CONCLUSION

In patients without diabetes, accurate measurement of fasting intact insulin levels by mass spectrometry constitutes an easy and noninvasive strategy to predict presence of NAFLD.

Association of NAFLD and Insulin Resistance with Non Metastatic Bladder Cancer Patients: A Cross-Sectional Retrospective Study

Among risk factors (apart from smoking) likely involved in bladder cancer (BCa), metabolic syndrome (MS), obesity and type 2 diabetes mellitus (T2DM) have been explored with contrasting results. In spite of these studies, there is little data on the association between nonalcoholic fatty liver disease (NAFLD), its main driver, i.e., insulin resistance (IR), and BCa. Implanting a cross-sectional retrospective study we tried to investigate both NAFLD and IR prevalence in a hospital based population of BCa patients. We studied laboratory data from 204 patients with histologically confirmed non metastatic BCa and 50 subjects with no BCa, but with bladder diseases (no Ca BD). We evaluated the presence of NAFLD by the triglycerides/glucose Index (TyG Index), using a cut-off of 0.59 and by the Aspartate Aminotransferase/Alanine Aminotransferase AST/ALT ratio. IR was assessed by the same TyG Index (cut-off 4.68) and the triglycerides/High-Density Lipoprotein HDL ratio (cut-off 2.197). The diagnosis of impaired fasting glucose (IFG), condition of prediabetes, as well as that of T2DM was assessed according to canonical guidelines. The TyG Index predicted NAFLD presence in both groups (p = 0.000), but the BCa group showed a major percentage of NAFLD cases with respect to no Ca BD group (59% versus 40%). A greater proportion of IR (47%) in BCa group than in no Ca BD one (37%) was evidenced by the TyG Index with its median value significantly different (p = 0.0092). This high rate of IR in the BCa group was confirmed by the triglycerides/HDL ratio (p = 0.02). Prediabetes and T2DM were more prevalent in the BCa group than no Ca BD group (p = 0.024). In this study a consistent NAFLD presence was found in BCa patients. This is an important comorbidity factor that deserves further consideration in prospective studies. The higher prevalence of NAFLD, IR, prediabetes and T2DM in the BCa group evidences the need that these disorders should be reckoned as adjunct factors that could impact on this cancerous disease.

Neue Klassifikation des Diabetes mellitus – Anforderungen an Labormessgrößen

Die bislang etablierte Klassifikation des Diabetes mellitus hat sich in der Praxis zwar bewährt, spiegelt aber die Heterogenität der Erkrankung nicht wider. In einer Clusteranalyse einer schwedischen Arbeitsgruppe wurde eine neue Klassifikation vorgeschlagen, die den Diabetes mellitus in 5 Subgruppen unterteilt. Diese unterscheiden sich maßgeblich in der Prädiktion und Therapie von Folgeerkrankungen von Menschen mit Diabetes. Zur Klassifikation wurden unter anderem GAD-Autoantikörper, HbA1c, HOMA2-B und HOMA2-IR verwendet, wobei die Berechnung der HOMA-Indizes auf den Messgrößen Glukose und Insulin beziehungsweise C-Peptid beruht. Die Messverfahren der dabei verwendeten Labormessgrößen müssen notwendigerweise standardisiert und damit vergleichbar sein. Erst dann kann diese Klassifikation weltweit angewendet werden. Unabhängig davon ist die Vergleichbarkeit von Laborergebnissen auch für die Diagnosestellung, Prädiktion und Therapiesteuerung von Menschen mit Diabetes zwingend notwendig. In den letzten Jahrzehnten wurden daher bei den diabetesrelevanten Labormessgrößen große Anstrengungen unternommen, um eine Standardisierung dieser Parameter zu erreichen. Für Glukose und HbA1c-Wert konnte dies inzwischen erreicht werden, sodass diese Parameter international vergleichbar gemessen werden. Der Prozess der Standardisierung der C-Peptid-Bestimmung soll 2020 fertiggestellt sein und anschließend umgesetzt werden. Dagegen ist die Standardisierung der Insulinbestimmung bisher nur unzureichend fortgeschritten. Die Bestimmung von GAD-Autoantikörpern kann aufgrund der biologischen Heterogenität von Autoantikörpern nicht standardisiert werden, jedoch ist in den letzten Jahren eine weitgehende Harmonisierung erzielt worden. Durch eine weltweite Standardisierung dieser Parameter können fehlerhafte Diagnosen und falsche klinische Entscheidungen, die auf Labormessgrößen beruhen, zum Nutzen der Patienten reduziert werden.

Design and fabrication of a smart sensor using in silico epitope mapping and electro-responsive imprinted polymer nanoparticles for determination of insulin levels in human plasma

A robust and highly specific sensor based on electroactive molecularly imprinted polymer nanoparticles (nanoMIP) was developed. The nanoMIP tagged with a redox probe, combines both recognition and reporting capabilities. The developed nanoMIP replaces enzyme-mediator pairs used in traditional biosensors thus, offering enhanced molecular recognition for insulin, improving performance in complex biological samples, and yielding high stability. Also, most of existing sensors show poor performance after storage. To improve costs of the logistics and avoid the need of cold storage in the chain supply, we developed an alternative to biorecognition system that relies on nanoMIP. NanoMIP were computationally designed using "in-silico" insulin epitope mapping and synthesized by solid phase polymerisation. The characterisation of the polymer nanoparticles was performed by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform Infrared (FT-IR) and surface plasmon resonance (SPR). The electrochemical sensor was developed by chemical immobilisation of the nanoMIP on screen printed platinum electrodes. The insulin sensor displayed satisfactory performances and reproducible results (RSD = 4.2%; n = 30) using differential pulse voltammetry (DPV) in the clinically relevant concentration range from 50 to 2000 pM. The developed nanoMIP offers the advantage of large number of specific recognition sites with tailored geometry, as the resultant, the sensor showed high sensitivity and selectivity to insulin with a limit of detection (LOD) of 26 and 81 fM in buffer and human plasma, respectively, confirming the practical application for point of care monitoring. Moreover, the nanoMIP showed adequate storage stability of 168 days, demonstrating the robustness of sensor for several rounds of insulin analysis.

Discordance between the triglyceride glucose index and fasting plasma glucose or HbA1C in patients with acute coronary syndrome undergoing percutaneous coronary intervention predicts cardiovascular events: a cohort study from China

Background

Previous studies have investigated the relationship of the triglyceride glucose (TyG) index with the incidence of cardiovascular events. However, to date, there have been no studies comparing the predictive values of fasting plasma glucose (FPG), glycosylated hemoglobin A (HbA1C) and the TyG index for the risk of cardiovascular events. This study aimed to use discordance analysis to evaluate and compare the effectiveness of FPG, HbA1C and the TyG index to predict the risk of cardiovascular events.

Methods

Patients diagnosed with acute coronary disease (ACS) undergoing percutaneous coronary intervention (PCI) were enrolled in this study. The TyG index was computed using the following formula: ln [fasting triglycerides (mg/dL) × FPG (mg/dL)/2]. We categorized patients into 4 concordance/discordance groups. Discordance was defined as a TyG index equal to or greater than the median and an FPG or HbA1C less than the median, or vice versa. The primary outcome was the composite of death, nonfatal myocardial infarction, nonfatal stroke and unplanned repeat revascularization. A Cox proportional hazards regression model was performed to estimate the risk of cardiovascular events according to the concordance/discordance groups. Sensitivity analysis was performed on each patient group divided into high or low categories for HbA1C or FPG and were repeated according to diabetes status.

Results

In total, 9285 patients were included in the final statistical analysis (male: 75.3%, age: 59.9 ± 10.05 years, BMI: 26.2 ± 9.21 kg/m², diabetes: 43.9% and dyslipidemia: 76.8%). The medians defining concordance/discordance were 6.19 mmol/L for FPG, 6.1% for HbA1C and 8.92 for the TyG index. The TyG index was strongly related to triglycerides and HDL-C (r = 0.881 and -0.323, respectively; both P < 0.001). During the 17.4 ± 2.69 months of follow-up, there were 480 (5.1%) incident cardiovascular events. Among patients with a lower HbA1C or FPG, 15.6% and 16.3%, respectively, had a discordantly high TyG index and a greater risk of cardiovascular events compared with patients with a concordantly low TyG index after full adjustment (HR: 1.92, 95% CI 1.33–2.77; HR: 1.89, 95% CI 1.38–2.59; for HbA1C and FPG, respectively). Repeat risk estimation using high or low categories for FPG or HbA1C and diabetes status confirmed the results.

Conclusions

Patients with a discordantly high TyG index had a significantly greater risk of cardiovascular events regardless of diabetes status. The TyG index might be a better predictor of cardiovascular risk than FPG or HbA1C for patients with ACS undergoing PCI. This discordance may support better cardiovascular risk management regardless of diabetes status.

Association of insulin resistance, from mid-life to late-life, with aortic stiffness in late-life: the Atherosclerosis Risk in Communities Study

Background

Insulin resistance may contribute to aortic stiffening that leads to end-organ damage. We examined the cross-sectional association and prospective association of insulin resistance and aortic stiffness in older adults without diabetes.

Methods

We analyzed 2571 men and women at Visit 5 (in 2011–2013), and 2350 men and women at repeat examinations from baseline at Visit 1 (in 1987–1989) to Visit 5 (in 2011–2013). Linear regression was used to estimate the difference in aortic stiffness per standard unit of HOMA-IR, TG/HDL-C, and TyG at Visit 5. Linear mixed effects were used to assess if high, as opposed to non-high, aortic stiffness (> 75th percentile) was preceded by a faster annual rate of change in log-HOMA-IR, log-TG/HDL-C, and log-TyG from Visit 1 to Visit 5.

Results

The mean age of participants was 75 years, 37% (n = 957) were men, and 17% (n = 433) were African American. At Visit 5, higher HOMA-IR, higher TG/HDL-C, and higher TyG were associated with higher aortic stiffness (16 cm/s per SD (95% CI 6, 27), 29 cm/s per SD (95% CI 18, 40), and 32 cm/s per SD (95% CI 22, 42), respectively). From Visit 1 to Visit 5, high aortic stiffness, compared to non-high aortic stiffness, was not preceded by a faster annual rate of change in log-HOMA-IR from baseline to 9 years (0.030 (95% CI 0.024, 0.035) vs. 0.025 (95% CI 0.021, 0.028); p = 0.15) or 9 years onward (0.011 (95% CI 0.007, 0.015) vs. 0.011 (95% CI 0.009, 0.013); p = 0.31); in log-TG/HDL-C from baseline to 9 years (0.019 (95% CI 0.015, 0.024) vs. 0.024 (95% CI 0.022, 0.026); p = 0.06) or 9 years onward (− 0.007 (95% CI − 0.010, − 0.005) vs. − 0.009 (95% CI − 0.010, − 0.007); p = 0.08); or in log-TyG from baseline to 9 years (0.002 (95% CI 0.002, 0.003) vs. 0.003 (95% CI 0.003, 0.003); p = 0.03) or 9 years onward (0 (95% CI 0, 0) vs. 0 (95% CI 0, 0); p = 0.08).

Conclusions

Among older adults without diabetes, insulin resistance was associated with aortic stiffness, but the putative role of insulin resistance in aortic stiffness over the life course requires further study.

Relationship Between Metabolic Syndrome and Beta-Cell Function in Nondiabetic Korean Premenopausal and Postmenopausal Women: 2015 Korean National Health and Nutrition Examination Survey

Background: This study was conducted to assess the relationship between metabolic syndrome (MetS) and beta-cell function in nondiabetic Korean women. Methods: This study included 2,507 women (premenopausal women, 1,359; postmenopausal women, 1,148) who were aged ≥20 and used 2015 Korean National Health and Nutrition Examination Survey (KNHANES) data. Results: Key study results were as follows: first, in both premenopausal and postmenopausal women, after adjusting for related variables [except body mass index (BMI)], MetS (P < 0.001) and metabolic syndrome score (MSS; P < 0.001) were positively associated with the homeostasis model assessment of beta-cell function (HOMA-B) levels. Second, in premenopausal women, when further adjusted for BMI, MetS (P = 0.002) and MSS (P < 0.001) were also positively associated with HOMA-B levels. However, in postmenopausal women, when further adjusting for BMI, the associations of MetS (P = 0.322) or MSS (P = 0.855) and HOMA-B levels were no longer significant. Conclusions: Metabolic syndrome was positively associated with beta-cell function in nondiabetic Korean premenopausal women, but not in Korean postmenopausal women.

Recent advances in the determination of insulins from biological fluids

The qualitative and quantitative determination of insulin and its related substances (e. g., C-peptide) is of great importance in many different areas of analytical chemistry. In particular, due to the steadily increasing prevalence of metabolic disorders such as diabetes mellitus, an adequate control of the circulating amount of insulin is desirable. In addition, also in forensics and doping control analysis, the determination of insulin in blood, urine or other biological matrices plays a major role. However, in order to establish general reference values for insulin and C-peptide for diabetology, the comparability of measured concentrations is indispensable. This has not yet been fully implemented, although enormous progress has been made in recent years, and the search for a "gold standard" method is still ongoing. In addition to established ligand-binding assays, an increasing number of mass-spectrometric methods have been developed and employed as the to-date available systems (for example, high-resolution/high accuracy mass spectrometers) provide the sensitivity required to determine analyte concentrations in the sub-ng/mL (sub-100pmol/L) level. Meanwhile, also high-throughput measurements have been realized to meet the requirement of testing a high number of samples in a short period of time. Further developments aim at enabling the online measurement of insulin in the blood with the help of an insulin sensor and, in the following, in addition to a brief review, today's state of the art testing developments are summarized.

Low doses of cocoa extract supplementation ameliorate diet-induced obesity and insulin resistance in rats

Cocoa polyphenols exhibit high antioxidant activity and have been proposed as a potential adjuvant for the treatment of metabolic disturbances. Here, we demonstrate that supplementation with low doses (14 and 140 mg per kg per rat) of a complete cocoa extract induces metabolic benefits in a diet-induced obesity (DIO) model of Wistar rats. After 10 weeks, cocoa extract-supplemented animals exhibited significantly lower body weight gain and food efficiency, with no differences in energy intake. Cocoa significantly reduced visceral (epididymal and retroperitoneal) and subcutaneous fat accumulation accompanied by a significant reduction in the adipocyte size, which was mediated by downregulation of the adipocyte-specific genes Cebpa, Fasn and Adipoq. Additionally, cocoa extract supplementation reduced the triacylglycerol/high density lipoprotein (TAG/HDL) ratio, decreased hepatic triglyceride accumulation, improved insulin sensitivity by reducing HOMA-IR, and significantly ameliorated glucose tolerance after an intraperitoneal glucose tolerance test. Finally, no adverse effect was observed in an in vivo toxicity evaluation of our cocoa extract at doses up to 500 mg kg^-1 day^-1. Our data demonstrate that low doses of cocoa extract supplementation (14 and 140 mg kg^-1 day^-1) are safe and sufficient to counteract obesity and type-2 diabetes in rats and provide new insights into the potential application of cocoa supplements in the management of the metabolic syndrome.

Preterm Birth as a Risk Factor for Metabolic Syndrome and Cardiovascular Disease in Adult Life: A Systematic Review and Meta-Analysis

OBJECTIVE

To determine if preterm birth is associated with components of the metabolic syndrome in adult life.

STUDY DESIGN

A structured literature search was performed using PubMed. All comparative studies reported metabolic and cardiovascular outcomes in adults (≥18 years of age) born preterm (<37 weeks of gestation) compared with adults born at term (37-42 weeks of gestation) and published through March 2018 were included. The major outcomes assessed were body mass index, waist circumference, waist-to-hip ratio, fat mass, systolic blood pressure (SBP), diastolic blood pressure (DBP), 24-hour SBP, 24-hour DBP, endothelium-dependent brachial artery flow-mediated dilation, carotid intima-media thickness, pulse wave velocity, fasting glucose and insulin, Homeostasis Model Assessment-Estimated Insulin Resistance Index, and lipid profiles. Quality appraisal was performed using a modified version of the Newcastle-Ottawa scale. A meta-analysis was performed for comparable studies which reported sufficient data.

RESULTS

Forty-three studies were included, including a combined total of 18 295 preterm and 294 063 term-born adults. Prematurity was associated with significantly higher fat mass (P = .03), SBP (P < .0001), DBP (P < .0001), 24-hour SBP (P < .001), and 24-hour DBP (P < .001). Furthermore, preterm-born adults presented higher values of fasting glucose (P = .01), insulin (P = .002), Homeostasis Model Assessment-Estimated Insulin Resistance Index (P = .05), and total cholesterol levels (P = .05) in comparison with adults born at term, in random effect models. No statistically significant difference was found between preterm and term-born adults for the other outcomes studied.

CONCLUSIONS

Preterm birth is strongly associated with a number of components of the metabolic syndrome and cardiovascular disease in adult life.

Ten-Year Legacy Effects of Three Eight-Month Exercise Training Programs on Cardiometabolic Health Parameters

Background: STRRIDE (Studies Targeting Risk Reduction Interventions through Defined Exercise) was an eight-month exercise study conducted from 1998-2003. Subjects were randomized to control or one of three exercise groups differing in intensity and amount. To determine if there were legacy effects, we invited 161 individuals who completed the intervention phase to return for a 10-year Reunion study. Methods: Subjects completed medical history and physical activity questionnaires. Height, body weight, blood pressure, waist circumference, and peak VO₂ were measured. Fasting blood samples were analyzed for glucose, insulin and lipids. Of 161 original subjects, 153 were within 10 years of STRRIDE completion. Of these, 28 were lost to follow-up and 21 declined to participate in the Reunion study. Overall, 104 subjects (83% eligible) participated. Change over time was computed as the 10-year Reunion value minus the pre-intervention value. Significant within group changes were calculated using two-tailed t-tests. ANCOVA determined differences among groups with pre-intervention values as covariates. Bonferroni corrections were applied to account for multiple comparisons. Results: Ten years after completing STRRIDE, there were a number of group-specific health and fitness legacy effects. Original participation in either the moderate intensity exercise or control group resulted in a 10.5% decrease in peak VO₂ over the ensuing 10 years. Conversely, both vigorous intensity groups experienced only a 4.7% decrement in cardiorespiratory fitness over that time period. As compared to controls, all three exercise groups experienced smaller increases in waist circumference. Those who participated in moderate intensity exercise experienced the greatest 10-year reduction in fasting insulin. Compared to all other groups, the moderate intensity subjects had greater reductions in mean arterial pressure at the Reunion timepoint. Summary: Ten years after completing a randomized eight-month exercise training intervention, previously sedentary individuals exhibited group-specific differences consistent with an intervention-based legacy effect on cardiorespiratory fitness and cardiometabolic parameters. These findings highlight the critical need to better understand the sustained legacy health effects of exercise training interventions.

Towards Point-of-Care Insulin Detection

Good glucose management through an insulin dose regime based on the metabolism of glucose helps millions of people worldwide manage their diabetes. Since Banting and Best extracted insulin, glucose management has improved due to the introduction of insulin analogues that act from 30 minutes to 28 days, improved insulin dose regimes, and portable glucose meters, with a current focus on alternative sampling sites that are less invasive. However, a piece of the puzzle is still missing-the ability to measure insulin directly in a Point-of-Care device. The ability to measure both glucose and insulin concurrently will enable better glucose control by providing an improved estimate for insulin sensitivity, minimizing variability in control, and maximizing safety from hypoglycaemia. However, direct detection of free insulin has provided a challenge due to the size of the molecule, the low concentration of insulin in blood, and the selectivity against interferants in blood. This review summarizes current insulin detection methods from immunoassays to analytical chemistry, and sensors. We also discuss the challenges and potential of each of the methods towards Point-of-Care insulin detection.

Abnormal Glucose Metabolism and Insulin Resistance Are Induced via the IRE1α/XBP-1 Pathway in Subclinical Hypothyroidism

Subclinical hypothyroidism (SCH) and diabetes mellitus are closely related and often occur together in individuals. However, the underlying mechanism of this association is still uncertain. In this study we re-analyzed the data of a mature database (NHANES, 1999 ~ 2002) and found that both fasting plasma glucose levels and the proportion of hyperglycemic subjects among SCH patients were higher than that found in euthyroid controls. SCH was also associated with a 2.29-fold increased risk for diabetes. Subsequently, we established an SCH mouse model and subjected it to an oral glucose tolerance test (OGTT) and an insulin tolerance test (ITT). SCH mice exhibited impaired glucose and insulin tolerance. Increased HOMA-IR and decreased ISI indexes, indicating insulin resistance (IR), were also observed in the SCH state. Hepatic ERp29 and Bip, as well as IRE1α and XBP-1s, were induced significantly in SCH mice, suggesting the induction of endoplasmic reticulum (ER) stress, particularly involving the IRE1α/XBP-1s pathway. Interestingly, when we relieved ER stress using 4-phenyl butyric acid, abnormal glucose metabolism, and IR status in SCH mice were improved. Our findings suggest that ER stress, predominantly involving the IRE1α/XBP-1s pathway, may play a pivotal role in abnormal glucose metabolism and IR in SCH that may help develop potential strategies for the prevention and treatment of diabetes.

Using simple clinical measures to predict insulin resistance or hyperglycemia in girls with polycystic ovarian syndrome

BACKGROUND

Polycystic ovarian syndrome (PCOS) includes insulin resistance (IR) and impaired glucose tolerance (IGT) in youth, and a greatly elevated risk of type 2 diabetes in adulthood. Identifying IR is challenging and documenting IGT requires an oral glucose tolerance test (OGTT).

OBJECTIVE

Identify easily applied surrogate measures for IR and IGT in girls with PCOS.

METHODS

We studied 28 girls with PCOS (body mass index [BMI] percentile 98 (83.99); 15.5 (14.5,16.6) years of age) and 20 with normal menses [BMI percentile (97 (88.99); 15.5 (13.3,16.1) years]. Hyperinsulinemic-euglycemic clamps (insulin dose of 80 μU/ml/min) to determine glucose infusion rate (GIR) and a 75 g OGTT were performed. Surrogates for IR including fasting insulin, homeostatic model assessment-insulin resistant (HOMA-IR), Matsuda index, and estimate of insulin sensitivity (e-IS) were compared to IGT status and GIR. Spearman correlations were performed between surrogates and GIR or IGT, and receiver operator curve (ROC) analysis to predict GIR below the median or IGT status.

RESULTS

GIR was lower in PCOS (12.9 ± 4.6 vs 17.1 ± 5.1 mg/kg fat-free mass·min; P = 0.01). Within PCOS, HOMA-IR (r = -0.78, P < 0.0001), e-IS (r = 0.70, P < 0.001), and Matsuda (r = 0.533, P < 0.001) correlated with GIR. e-IS provided a good sensitivity (100%) and specificity (71%) to identify IR (e-IS cutoff: <6.3, ROC-area under curve = 0.898). Fasting insulin >22 IU/mL had the best sensitivity (88%), specificity (78%), and ROC (0.760) for IGT status.

CONCLUSIONS

Girls with PCOS have significant IR, and IGT is common. Both e-IS and fasting insulin are obtainable without an OGTT or clamp and could be used clinically to guide treatment in PCOS.

Short-Term Repeatability of Insulin Resistance Indexes in Older Adults: The Atherosclerosis Risk in Communities Study

CONTEXT

The homeostatic model assessment of insulin resistance (HOMA-IR) and triglyceride (TG)/high-density lipoprotein cholesterol (HDL-C) ratio (TG/HDL-C) are insulin resistance indexes routinely used in clinical and population-based studies; however, their short-term repeatability is not well characterized.

OBJECTIVE

To quantify the short-term repeatability of insulin resistance indexes and their analytes, consisting of fasting glucose and insulin for HOMA-IR and TG and HDL-C for TG/HDL-C.

DESIGN

Prospective cohort study.

PARTICIPANTS

A total of 102 adults 68 to 88 years old without diabetes attended an initial examination and repeated examination (mean, 46 days; range, 28 to 102 days). Blood samples were collected, processed, shipped, and assayed following a standardized protocol.

MAIN OUTCOME MEASURES

Repeatability was quantified using the intraclass correlation coefficient (ICC) and within-person coefficient of variation (CV). Minimum detectable change (MDC95) and minimum detectable difference with 95% confidence (MDD95) were quantified.

RESULTS

For HOMA-IR, insulin, and fasting glucose, the ICCs were 0.70, 0.68, and 0.70, respectively; their respective within-person CVs were 30.4%, 28.8%, and 5.6%. For TG/HDL-C, TG, and HDL-C, the ICCs were 0.80, 0.68, and 0.91, respectively; their respective within-person CVs were 23.0%, 20.6%, and 8.2%. The MDC95 was 2.3 for HOMA-IR and 1.4 for TG/HDL-C. The MDD95 for a sample of n = 100 was 0.8 for HOMA-IR and 0.6 for TG/HDL-C.

CONCLUSIONS

Short-term repeatability was fair to good for HOMA-IR and excellent for TG/HDL-C according to suggested benchmarks, reflecting the short-term variability of their analytes. These measurement properties can inform the use of these indexes in clinical and population-based studies.

Claimed effects, outcome variables and methods of measurement for health claims proposed under European Community Regulation 1924/2006 in the area of blood glucose and insulin concentrations

Most requests for authorization to bear health claims under Articles 13(5) and 14 related to blood glucose and insulin concentration/regulation presented to the European Food Safety Authority (EFSA) receive a negative opinion. Reasons for such decisions are mainly ascribable to poor substantiation of the claimed effects. In this scenario, a project was carried out aiming at critically analysing the outcome variables (OVs) and methods of measurement (MMs) to be used to substantiate health claims, with the final purpose to improve the quality of applications provided by stakeholders to EFSA. This manuscript provides a position statement of the experts involved in the project, reporting the results of an investigation aimed to collect, collate and critically analyse the information relevant to claimed effects (CEs), OVs and MMs related to blood glucose and insulin levels and homoeostasis compliant with Regulation 1924/2006. The critical analysis of OVs and MMs was performed with the aid of the pertinent scientific literature and was aimed at defining their appropriateness (alone or in combination with others) to support a specific CE. The results can be used to properly select OVs and MMs in a randomized controlled trial, for an effective substantiation of the claims, using the reference method(s) whenever available. Moreover, results can help EFSA in updating the guidance for the scientific requirements of health claims.

A pragmatic bottom-up approach to harmonize the units of clinical chemistry tests among Belgian clinical laboratories, focusing on immunoassays

Background:

Harmonization of units is an important step to improve the comparability of clinical chemistry results, but few examples exist of successful harmonization efforts. We present the results of a pragmatic approach that was implemented in Belgium from 2012.

Methods:

After a large consultation and information of stakeholders, preferred units were proposed for 140 assays, including the 23 immunoassays discussed in more detail here. The change occurred in two phases, first involving assays for which there was no change in the numerical result, then changes involving a change in numerical results. Laboratories were invited to participate in this harmonization on a voluntary basis. The project was based on a bottom-up approach, large consultation and the pragmatic choice of the proposed units, including conventional and SI units.

Results:

The large heterogeneity of units was drastically reduced; adoption of the preferred units increased from 3% (insulin) – 45% (HCG) to 70% (insulin) – 96% (LH and FSH). Adoption of the preferred units was higher if it involved no change in numerical values (90%) than when there was a change (76%).

Conclusions:

We believe that the harmonization effort has reached its goals. Without aiming at implementing SI units for all parameters, our strategy was successful with a large majority of the laboratories switching to the proposed units. Moreover, the harmonization program is still progressing, with additional laboratories converting to the consensus units.

Assay-dependent variability of serum insulin concentrations: a comparison of eight assays

Although insulin measurement is essential for both clinical and research purposes, there is currently no reference method for insulin assays. The aim of this study was to compare results of serum insulin determined by a number of commercially available assays. We compared eight insulin assays by analyzing 165 serum samples. Assays included two chemiluminescence (Roche and DiaSorin), four ELISA (Tosoh, Mercodia, Monobind, and Diametra), and two IRMA (Izotop and BioSource) methods. Each assay was compared with the mean of all assay methods and Bland-Altman difference plots were used to measure agreement between each assay and overall mean. Least squared perpendicular distance regression analysis (Deming's method) was used to calculate slope and intercept for bias and also for each assay vs. mean of eight assays. Findings showed that the lowest and highest median insulin concentrations varied by a factor of 1.8. Maximum and minimum correlations with mean of assays were observed for Roche (0.992) and BioSource (0.844), respectively. Significant bias was observed in six assays. In pairwise comparisons of different assays, the highest and least mean differences were 7.78 μU/mL and -0.14 μU/mL, respectively. In conclusion, serum insulin measurement with different assays showed a maximum of 1.8-fold difference, a point that should be taken into consideration in the interpretation of circulating insulin levels in both clinical and research fields.

Use of Biomarkers in Predicting the Onset, Monitoring the Progression, and Risk Stratification for Patients with Type 2 Diabetes Mellitus

BACKGROUND

As the worldwide prevalence of type 2 diabetes mellitus (T2DM) increases, it is even more important to develop cost-effective methods to predict and diagnose the onset of diabetes, monitor progression, and risk stratify patients in terms of subsequent cardiovascular and diabetes complications.

CONTENT

Nonlaboratory clinical risk scores based on risk factors and anthropomorphic data can help identify patients at greatest risk of developing diabetes, but glycemic indices (hemoglobin A1c, fasting plasma glucose, and oral glucose tolerance tests) are the cornerstones for diagnosis, and the basis for monitoring therapy. Although family history is a strong predictor of T2DM, only small populations of patients carry clearly identifiable genetic mutations. Better modalities for detection of insulin resistance would improve earlier identification of dysglycemia and guide effective therapy based on therapeutic mechanisms of action, but improved standardization of insulin assays will be required. Although clinical risk models can stratify patients for subsequent cardiovascular risk, the addition of cardiac biomarkers, in particular, high-sensitivity troponin and natriuretic peptide provide, significantly improves model performance and risk stratification.

CONCLUSIONS

Much more research, prospectively planned and with clear treatment implications, is needed to define novel biomarkers that better identify the underlying pathogenic etiologies of dysglycemia. When compared with traditional risk features, biomarkers provide greater discrimination of future risk, and the integration of cardiac biomarkers should be considered part of standard risk stratification in patients with T2DM.

Reference intervals for C-peptide and insulin derived from a general adult Danish population

BACKGROUND

Despite international efforts to standardize C-peptide and insulin calibrators and immunoassays, platform dependent differences still exist, and platform specific reference intervals are hence needed for correct interpretation. We therefore wanted to establish traceable reference intervals for C-peptide and insulin.

METHODS

In 623 consecutively recruited participants, insulin and C-peptide were measured using the Cobas e411 (Roche Diagnostics, Switzerland). Participants with diabetes were excluded (fasting Glucose ≥7.0mmol/L or HbA1c≥6.5%/≥48mmol/L) and reference intervals were calculated with and without the inclusion of persons who were prediabetic, according to two definitions (The World Health Organization (WHO) and American Diabetes Association (ADA)). To ensure the correctness of calibration, the control pools were analyzed by a reference laboratory. The reference intervals were calculated according to the IFCC guidelines, using the RefVal software (Solberg, Oslo, Norway).

RESULTS

Comparison of our results with those from the reference laboratory revealed equivalence for C-peptide results whereas the insulin determined on the Cobas e411 assay were 15-20% higher. The difference is attributed to an incorrect conversion factor for converting from activity to metric units. The Cobas e411 assay uses the factor 6.945 for converting from U/mL to pmol/L. This is in disagreement with the biological activity of insulin which is 166.8×10⁶IU/mol or 6.00nmol/IU.

CONCLUSION

We successfully established reference intervals for C-peptide and insulin for non-diabetic and prediabetic participants. The reference intervals for fasting C-peptide and fasting insulin are ready for implementation. A recertification of the insulin standards is needed.

Relationship between homeostasis model assessment of insulin resistance and beta cell function and serum 25-hydroxyvitamin D in non-diabetic Korean adults

The purpose of this study is to look at these relationships in non-diabetic Korean adults. This study was based on data from the KNHANES V-1, which is representative of the population of Korea. A total of 5,492 participants (≥20 years in age) without type 1 or type 2 diabetes, assessed for serum 25-hydroxyvitamin D [25(OH)D], fasting blood glucose and insulin, as well as anthropometric variables, were included in the analyses. The key study results were as follows: First, vitamin D status [vitamin D deficient, 25(OH)D <25 nM; vitamin D insufficient, 25(OH)D ≥25, <50 nM; vitamin D sufficient, 25(OH)D ≥50 nM] was inversely associated with homeostasis model assessment of insulin resistance (HOMA-IR) and beta cell function (HOMA-B) in model 2 (adjusted for age and gender) and 3 (further adjusted for smoking, alcohol drinking, regular exercise, systolic and diastolic blood pressure, waist circumference, and body mass index). Second, in model 4, when further adjusted for total cholesterol, triglycerides, and HDL-C, vitamin D status was inversely associated with HOMA-B. However, association of vitamin D status and HOMA-IR was no longer significant. In conclusion, vitamin D was inversely associated with beta cell function in non-diabetic Korean adults but was not associated with insulin resistance.

Relationship between metabolic syndrome and metabolic syndrome score and beta cell function by gender in Korean populations with obesity

The present study was conducted to assess the relationships between metabolic syndrome and metabolic syndrome score (MSS) and beta cell function by gender in Korean populations with obesity. This study included 1,686 adults aged 20 or older using the 2010 Korea National Health and Nutrition Examination Survey (KNHANES) data, which represent national data in Korea. The key study results were as follows: First, in men, after adjusting for related variables (including body mass index), metabolic syndrome (p=0.005) and MSS (p=0.018) were inversely associated with the homeostatic model assessment of beta cell function (HOMA-B) values. Second, in women, after adjusting for related variables, metabolic syndrome (p=0.616) and MSS (p=0.929) were not associated with HOMA-B levels. In conclusion, metabolic syndrome and MSS were inversely associated with beta cell function in Korean men with obesity, but not in Korean women with obesity.

Disproportionately Elevated Proinsulin Levels as an Early Indicator of β-Cell Dysfunction in Nondiabetic Offspring of Chinese Diabetic Patients

Objective. To study the characteristics of β-cell dysfunction and insulin resistance (IR) in the first-degree relatives (FDRs) of T2DM in Chinese population and to examine the usefulness of proinsulin (PI) for evaluating β-cell dysfunction. Methods. 229 subjects of nondiabetic FDRs, 71 newly diagnosed T2DM, and 114 with normal glucose tolerance (NGT) but not FDRs (NGT-non-FDRs) were verified by a 2-hour oral glucose tolerance test. Specific insulin (SI) and PI were measured by highly sensitive ELISA. Results. Compared to NGT-non-FDRs, NGT-FDRs showed higher levels of fasting and 2-hour PI, fasting PI-to-SI ratio (FPI/SI), and HOMA-IR (p < 0.01). Meanwhile, fasting PI, FPI/SI, and HOMA-IR were increased steadily from NGT-FDRs to prediabetes-FDRs and were highest in T2DM group (p < 0.001), whereas a significant decrease in HOMA-B could be observed only in T2DM group. Moreover, a progressive deterioration of β-cell function in NGT-FDRs, prediabetes-FDRs, and T2DM could be identified by FPI/SI even after adjusting for HOMA-IR: relative to non-FDRs controls, mean FPI/SI levels were increased 1.5, 2.0, and 4.7-fold, respectively (all p < 0.01). Conclusions.  β-cell dysfunction as assessed by disproportionate secretion of proinsulin and IR by HOMA (using specific insulin assay) already exist in FDRs of T2DM even with normal glucose status. Compared with HOMA-B, FPI/SI could detect β-cell failure in earlier stage of diabetes development.

Relationship between homeostasis model assessment of insulin resistance and beta cell function and serum 25-hydroxyvitamin D in non-diabetic Korean adults

The purpose of this study is to look at these relationships in non-diabetic Korean adults. This study was based on data from the KNHANES V-1, which is representative of the population of Korea. A total of 5,492 participants (≥20 years in age) without type 1 or type 2 diabetes, assessed for serum 25-hydroxyvitamin D [25(OH)D], fasting blood glucose and insulin, as well as anthropometric variables, were included in the analyses. The key study results were as follows: First, vitamin D status [vitamin D deficient, 25(OH)D <25 nM; vitamin D insufficient, 25(OH)D ≥25, <50 nM; vitamin D sufficient, 25(OH)D ≥50 nM] was inversely associated with homeostasis model assessment of insulin resistance (HOMA-IR) and beta cell function (HOMA-B) in model 2 (adjusted for age and gender) and 3 (further adjusted for smoking, alcohol drinking, regular exercise, systolic and diastolic blood pressure, waist circumference, and body mass index). Second, in model 4, when further adjusted for total cholesterol, triglycerides, and HDL-C, vitamin D status was inversely associated with HOMA-B. However, association of vitamin D status and HOMA-IR was no longer significant. In conclusion, vitamin D was inversely associated with beta cell function in non-diabetic Korean adults but was not associated with insulin resistance.

Glycated Hemoglobin, Fasting Insulin and the Metabolic Syndrome in Males. Cross-Sectional Analyses of the Aragon Workers' Health Study Baseline

Background and Aims

Glycated hemoglobin (HbA1c) is currently used to diagnose diabetes mellitus, while insulin has been relegated to research. Both, however, may help understanding the metabolic syndrome and profiling patients. We examined the association of HbA1c and fasting insulin with clustering of metabolic syndrome criteria and insulin resistance as two essential characteristics of the metabolic syndrome.

Methods

We used baseline data from 3200 non-diabetic male participants in the Aragon Workers' Health Study. We conducted analysis to estimate age-adjusted odds ratios (ORs) across tertiles of HbA1c and insulin. Fasting glucose and Homeostatic model assessment - Insulin Resistance were used as reference. Here we report the uppermost-to-lowest tertile ORs (95%CI).

Results

Mean age (SD) was 48.5 (8.8) years and 23% of participants had metabolic syndrome. The ORs for metabolic syndrome criteria tended to be higher across HbA1c than across glucose, except for high blood pressure. Insulin was associated with the criteria more strongly than HbA1c and similarly to Homeostatic model assessment - Insulin Resistance (HOMA-IR). For metabolic syndrome, the OR of HbA1c was 2.68, of insulin, 11.36, of glucose, 7.03, and of HOMA-IR, 14.40. For the clustering of 2 or more non-glycemic criteria, the OR of HbA1c was 2.10, of insulin, 8.94, of glucose, 1.73, and of HOMA-IR, 7.83. All ORs were statistically significant. The areas under the receiver operating characteristics curves for metabolic syndrome were 0.670 (across HbA1c values) and 0.770 (across insulin values), and, for insulin resistance, 0.647 (HbA1c) and 0.995 (insulin). Among non-metabolic syndrome patients, a small insulin elevation identified risk factor clustering.

Conclusions

HbA1c and specially insulin levels were associated with metabolic syndrome criteria, their clustering, and insulin resistance. Insulin could provide early information in subjects prone to develop metabolic syndrome.

Gut microbiota-based translational biomarkers to prevent metabolic syndrome via nutritional modulation

In the face of the global epidemic of metabolic syndrome (MetS) and its strong association with the increasing rate of cardiovascular morbidity and mortality, it is critical to detect MetS at an early stage in the clinical setting to implement preventive intervention long before the complications arise. Lipopolysaccharide, the cell wall component of Gram-negative bacteria produced from diet-disrupted gut microbiota, has been shown to induce metabolic endotoxemia, chronic low-grade inflammation, and ultimately insulin resistance. Therefore, ameliorating the inflammation and insulin resistance underlying MetS by gut microbiota-targeted, dietary intervention has gained increasing attention. In this review, we propose using dynamic monitoring of a set of translational biomarkers related with the etiological role of gut microbiota, including lipopolysaccharide binding protein (LBP), C-reactive protein (CRP), fasting insulin, and homeostasis model assessment of insulin resistance (HOMA-IR), for early detection and prevention of MetS via nutritional modulation. LBP initiates the recognition and monomerization of lipopolysaccharide and amplifies host immune responses, linking the gut-derived antigen load and inflammation indicated by the plasma levels of CRP. Fasting plasma insulin and HOMA-IR are measured to evaluate insulin sensitivity that is damaged by pro-inflammatory cytokines. The dynamic monitoring of these biomarkers in high-risk populations may provide translational methods for the quantitative and dynamic evaluation of dysbiosis-induced insulin resistance and the effectiveness of dietary treatment for MetS.

Glucose metabolism after renal transplantation

OBJECTIVE

We determined prevalence, risk factors, phenotype, and pathophysiological mechanism of new-onset diabetes after transplantation (NODAT) to generate strategies for optimal pharmacological management of hyperglycemia in NODAT patients.

RESEARCH DESIGN AND METHODS

Retrospective cohort study comparing demographics, laboratory data, and oral glucose tolerance test (OGTT)-derived metabolic parameters from kidney transplant recipients versus subjects not receiving transplants.

RESULTS

Among 1,064 stable kidney transplant recipients (≥ 6 months posttransplantation), 113 (11%) had a history of NODAT and 132 (12%) had pretransplant diabetes. In the remaining patients, randomly assigned OGTTs showed a high prevalence of abnormal glucose metabolism (11% diabetes; 32% impaired fasting glucose, impaired glucose tolerance, or both), predominantly in older patients who received tacrolimus as the primary immunosuppressant. Compared with 1,357 nontransplant subjects, stable kidney transplant recipients had lower basal glucose, higher glycated hemoglobin, lower insulin secretion, and greater insulin sensitivity in each of the three subgroups, defined by OGTT 2-h glucose (<140, 140-199, ≥ 200 mg/dL). These findings were reinforced in linear spline interpolation models of insulin secretion and sensitivity (all P < 0.001) and in another regression model in which the estimated oral glucose insulin sensitivity index was substantially higher (by 79-112 mL/min m(2)) for transplant versus nontransplant subjects despite adjustments for age, sex, and BMI (all P < 0.001).

CONCLUSIONS

Glucose metabolism differs substantially between kidney transplant recipients and nontransplant controls. Because impaired insulin secretion appears to be the predominant pathophysiological feature after renal transplantation, early therapeutic interventions that preserve, maintain, or improve β-cell function are potentially beneficial in this population.