EDTA improves stability of whole blood C-peptide and insulin to over 24 hours at room temperature

Concentrations of arsenic (As), cadmium (Cd) and lead (Pb) in blood, hair and semen of stallions in Finland

Heavy metal contamination poses significant environmental and health risks to both humans and animals. This study investigates the concentrations of arsenic (As), cadmium (Cd), and lead (Pb) in blood, hair, and semen samples collected from 16 breeding stallions in Western Finland to assess whether concentrations in hair and serum samples represent concentrations in semen. The analysis was conducted using an inductively coupled plasma mass spectrometry (ICP-MS) system. Results showed that hair samples exhibited the highest concentrations of heavy metals, particularly Pb and As, while semen showed the lowest levels. No significant correlations were found between the concentrations of heavy metals in blood and semen, or between hair and semen, indicating that blood and hair may not reliably predict metal content in semen. This study is the first to compare Pb, As, and Cd levels in hair, blood, and semen of Finnish stallions and highlights hair as a promising non-invasive biomarker of heavy metal exposure. The results underline hair's potential as a reliable long-term biomarker due to its ability to accumulate metals over time.

Insulin-Related Suicides-3 Cases

Insulin is a pancreas-produced hormone, which is essential for normal life. In persons with diabetes, who lack sufficient production of endogenous insulin, the availability of exogenously-produced and administered insulin represents an extremely valuable, life-preserving medical advancement. Unfortunately, as with many other medications, overdosage with insulin can and does occur, sometimes in an intentional suicidal manner. Another possible insulin-related suicidal action involves the intentional cessation of insulin therapy by someone who relies on insulin for survival. In this case series, we present 3 cases of insulin-related suicides, including two related to intentional insulin overdose and one where a known diabetic purposefully stopped taking insulin in order to commit suicide.

Evaluation of type 1 diabetes' partial clinical remission after three years of heterologous adipose tissue derived stromal/stem cells transplantation associated with vitamin D supplementation

BACKGROUND

Mesenchymal stem cell infusion and vitamin D supplementation may have immunomodulatory actions that could prolong the preservation of residual insulin secretion in patients with type 1 diabetes (T1D). Intervention with these agents after onset of T1D could favor the development of a remission phase, with potential clinical impact. We aimed to compare the presence of clinical remission (CR), glycemic control and daily insulin requirement at 6, 12, 18, 24 and 36 months after the diagnosis of T1D using IDAA1c in patients who received therapy with adipose tissue-derived mesenchymal stem cell (ASC) infusion and vitamin D supplementation and a control group.

METHODS

This retrospective cohort study analyzed data from the medical records of patients with T1D diagnosed between 15 and 40 years. Partial CR was defined as an IDAA1c index < 9. Patients in the intervention group received an infusion of adipose tissued-derived mesenchymal stem cells (ASCs) within 3 months after diagnosis and supplementation with 2000 IU of cholecalciferol for 1 year, started on the day following the infusion. Partial CR was also determined using the ISPAD criteria, to assess its agreement with IDAA1c.

RESULTS

A total of 28 patients were evaluated: 7 in the intervention group (group 1) and 21 in the control group (group 2). All patients in group 1 evolved with partial CR while only 46.7% of patients in group 2 had this outcome. Group 1 had a higher frequency of CR when evaluated with IDAA1c and ISPAD criteria. The mean duration of CR varied between the two criteria. Although HbA1c was similar between groups during follow-up, group 1 had a lower total daily insulin requirement (p < 0.005) at all time points. At 36 months, group 1 used 49% of the total daily insulin dose used by group 2 with similar glycemic control.

CONCLUSION

The intervention with infusion of ASC + vitamin D supplementation was associated with partial CR at 6 months. Although there were no differences in CR established by the IDAA1c and ISPAD criteria after three years of follow-up, patients who underwent intervention had nearly the half insulin requirement of controls with conventional treatment, with similar glycemic control.

TRIAL REGISTRATION

37001514.0.0000.5257.

Future clinical prospects of C-peptide testing in the early diagnosis of gestational diabetes

Gestational diabetes is typically diagnosed in the late second or third trimester of pregnancy. It is one of the most common metabolic disorders among expectant mothers, with potential serious short- and long-term complications for both maternal and offspring health. C-peptide is secreted from pancreatic beta-cells into circulation in equimolar amounts with insulin. It is a useful biomarker to estimate the beta-cell function because it undergoes negligible hepatic clearance and consequently it has a longer half-life compared to insulin. Pregnancy induces increased insulin resistance due to physiological changes in hormonal and metabolic homeostasis. Inadequate compensation by islet beta-cells results in hyperglycemia. The standard oral glucose tolerance test at 24-28 wk of gestation sets the diagnosis. Accumulated evidence from prospective studies indicates a link between early pregnancy C-peptide levels and the risk of subsequent gestational diabetes. Elevated C-peptide levels and surrogate glycemic indices at the beginning of pregnancy could prompt appropriate strategies for secondary prevention.

The stability of C-peptide and insulin in plasma and serum samples under different storage conditions

OBJECTIVES

C-peptide and insulin are peptide hormones and their stability is affected by a number of pre-analytical factors. The study aimed to investigate the impact of sample type, storage temperature and time delays before centrifugation and analysis on the stability of C-peptide and insulin.

METHODS

Ten healthy non-diabetic adults in fasting and non-fasting state were enrolled. 40 mL of blood was collected from each participant into SST and dipotassium EDTA tubes. Samples were centrifuged immediately or at timed intervals (8, 12, 48 and 72 h). After baseline measurements on the Roche Cobas e602 analyzer using electrochemiluminescence immunoassays, aliquots were stored at room temperature (RT), 2-8 and -20 °C for 4 h to 30 days. The percentage deviation (PD) from baseline was calculated and a change greater than desirable biological variation total error was considered clinically significant.

RESULTS

C-peptide was more stable in separated serum than plasma (PD of -5 vs. -13 %) samples stored at 2-8 °C for 7 days and was most unstable at RT when centrifugation was delayed (PD -46 % in plasma and -74 % in serum after 48 h). Insulin was more stable in plasma than in serum under the different storage conditions with a minimum PD of -1% when stored at -20 °C for 30 days. When samples were kept unspun at RT for 72 h, PD was -23 and -80 % in plasma and serum, respectively.

CONCLUSIONS

C-peptide was more stable in serum provided the sample was centrifuged immediately and stored in the fridge or freezer while insulin was found to be more stable in EDTA plasma.

Influence of Preservatives on Insulin in Postmortem Blood: Application to a Case of Insulin Aspart Suicide

Insulin aspart (NovoRapid®, NovoMix®, Novolog® and Fiasp®) is a fast-acting analog of human insulin, indicated in the treatment of type I and II diabetes. It is administered before meals to mimic the physiological insulin secretion that follows a rise in blood glucose. Its misuse for the purposes of suicide and murder and in the context of factitious order has often been described. In forensic medicine, the identification of insulin in biological samples has always been complex. In this paper, we present a case of suicide of a 64-year-old man who died after the injection of insulin aspart. He was suffering from terminal lung cancer and left a letter explaining the reasons for his suicide. Four empty NovoRapid® pens were found near the body. Body examination was unremarkable, and the femoral blood was collected in two dry Vacutainer™ tubes (red cap) and two sodium fluoride (NaF) tubes (gray cap). A liquid chromatography coupled to high-resolution mass spectrometry method was used to identify and discriminate insulin aspart from human insulin after immunopurification in the blood samples and in the pens. Blood specimens tested positive for insulin aspart with the concentrations of 36 and 37 ng/mL in dry tubes and 58 and 71 ng/mL in tubes containing NaF when tested ∼3 weeks after the collection of the specimens. The contents of the pens also matched with insulin aspart. The stability of insulin in blood is a critical point in the interpretation of the concentrations due to their rapid decrease caused by the activity of proteases in blood. During a degradation study implemented to compare three preservatives and dry tubes, suitable insulin aspart stability was observed with disodium salt of ethylenediaminetetracetic acid and NaF. Given that NaF is standard in forensic toxicology for measuring blood alcohol concentrations, the authors suggest its use for blood collection when insulin intoxication is suspected.

Analyzing bronchoalveolar fluid derived small extracellular vesicles using single-vesicle SERS for non-small cell lung cancer detection

An emerging body of research by biologists and clinicians has demonstrated the clinical application of small extracellular vesicles (sEVs, also commonly referred to as exosomes) as biomarkers for cancer detections. sEVs isolated from various body fluids such as blood, saliva, urine, and cerebrospinal fluid have been used for biomarker discoveries with highly encouraging outcomes. Among the biomarkers discovered are those responsible for multiple cancer types and immune responses. These biomarkers are recapitulated from the tumor microenvironments. Yet, despite numerous discussions of sEVs in scientific literature, sEV-based biomarkers have so far played only a minor role for cancer diagnostics in the clinical setting, notably less so than other techniques such as imaging and biopsy. In this paper, we report the results of a pilot study (n = 10 from each of the patient and the control group) using bronchoalveolar lavage fluid to determine the presence of sEVs related to non-small cell lung cancer in twenty clinical samples examined using surface enhanced Raman spectroscopy (SERS).

Linking Physical Activity to Breast Cancer Risk via the Insulin/Insulin-like Growth Factor Signaling System, Part 2: The Effect of Insulin/Insulin-like Growth Factor Signaling on Breast Cancer Risk

Perturbation of the insulin/insulin-like growth factor (IGF) signaling system is often cited as a mechanism driving breast cancer risk. A systematic review identified prospective cohort studies and Mendelian randomization studies that examined the effects of insulin/IGF signaling (IGF, their binding proteins (IGFBP), and markers of insulin resistance] on breast cancer risk. Meta-analyses generated effect estimates; risk of bias was assessed and the Grading of Recommendations Assessment, Development and Evaluation system applied to evaluate the overall quality of the evidence. Four Mendelian randomization and 19 prospective cohort studies met our inclusion criteria. Meta-analysis of cohort studies confirmed that higher IGF-1 increased risk of breast cancer; this finding was supported by the Mendelian randomization studies. IGFBP-3 did not affect breast cancer. Meta analyses for connecting-peptide and fasting insulin showed small risk increases, but confidence intervals were wide and crossed the null. The quality of evidence obtained ranged from 'very low' to 'moderate'. There were insufficient studies to examine other markers of insulin/IGF signaling. These findings do not strongly support the biological plausibility of the second part of the physical activity-insulin/IGF signaling system-breast cancer pathway. Robust conclusions cannot be drawn due to the dearth of high quality studies. See related article by Swain et al., p. 2106.

Precision medicine in type 1 diabetes

First envisioned by early diabetes clinicians, a person-centred approach to care was an aspirational goal that aimed to match insulin therapy to each individual's unique requirements. In the 100 years since the discovery of insulin, this goal has evolved to include personalised approaches to type 1 diabetes diagnosis, treatment, prevention and prediction. These advances have been facilitated by the recognition of type 1 diabetes as an autoimmune disease and by advances in our understanding of diabetes pathophysiology, genetics and natural history, which have occurred in parallel with advancements in insulin delivery, glucose monitoring and tools for self-management. In this review, we discuss how these personalised approaches have improved diabetes care and how improved understanding of pathogenesis and human biology might inform precision medicine in the future.

Gold Nanopyramid Arrays for Non-Invasive Surface-Enhanced Raman Spectroscopy-Based Gastric Cancer Detection via sEVs

Gastric cancer (GC) is one of the most common and lethal types of cancer affecting over one million people, leading to 768,793 deaths globally in 2020 alone. The key for improving the survival rate lies in reliable screening and early diagnosis. Existing techniques including barium-meal gastric photofluorography and upper endoscopy can be costly and time-consuming and are thus impractical for population screening. We look instead for small extracellular vesicles (sEVs, currently also referred as exosomes) sized ⌀ 30-150 nm as a candidate. sEVs have attracted a significantly higher level of attention during the past decade or two because of their potentials in disease diagnoses and therapeutics. Here, we report that the composition information of the collective Raman-active bonds inside sEVs of human donors obtained by surface-enhanced Raman spectroscopy (SERS) holds the potential for non-invasive GC detection. SERS was triggered by the substrate of gold nanopyramid arrays we developed previously. A machine learning-based spectral feature analysis algorithm was developed for objectively distinguishing the cancer-derived sEVs from those of the non-cancer sub-population. sEVs from the tissue, blood, and saliva of GC patients and non-GC participants were collected (n = 15 each) and analyzed. The algorithm prediction accuracies were reportedly 90, 85, and 72%. "Leave-a-pair-of-samples out" validation was further performed to test the clinical potential. The area under the curve of each receiver operating characteristic curve was 0.96, 0.91, and 0.65 in tissue, blood, and saliva, respectively. In addition, by comparing the SERS fingerprints of individual vesicles, we provided a possible way of tracing the biogenesis pathways of patient-specific sEVs from tissue to blood to saliva. The methodology involved in this study is expected to be amenable for non-invasive detection of diseases other than GC.

Analysis of insulin resistance using the non-linear homeostatic model assessment index in overweight canines

Background and Aim:

Diabetes mellitus is a carbohydrate metabolism disorder produced mainly by a deficit in insulin production or insulin resistance. The homeostatic model assessment (HOMA) is a broad method for estimating insulin resistance and β-cell function. This study aimed to evaluate the stages of insulin resistance using non-linear HOMA index analysis in normoglycemic normal weight and obese canines.

Materials and Methods:

Insulin resistance was evaluated using the mathematical HOMA non-linear model in canines with different body and glycemic conditions. Forty canines were studied, including 20 normoglycemic normal weight canines and 20 normoglycemic obese canines. Chi-square statistical test was applied, in which the body condition and HOMA non-linear index were evaluated. The Spearman correlation test was conducted to evaluate the glycemic and insulin variables in both types of canines.

Results:

The Spearman correlation presented a correlation between increased blood glucose levels and insulin in obese canines, with a correlation of 0.79, while no significant changes in insulin were found in normal weight canines with different blood glucose levels, with a correlation of −0.11. The analysis of the non-linear HOMA index showed significant differences between non-linear HOMA insulin resistance in normal weight and obese canines, with a Chi-square statistic of 16.9424 and p = 0.000039. Canine with increased HOMA 2 showed higher levels of insulin with increasing blood glucose compared to those with normal HOMA 2.

Conclusion:

The HOMA 2 is a marker for evaluating increased insulin resistance in obese dogs and can be used to determine patients at risk for glycemic alterations.

Partial Clinical Remission of Type 1 Diabetes: The Need for an Integrated Functional Definition Based on Insulin-Dose Adjusted A1c and Insulin Sensitivity Score

Despite advances in the characterization of partial clinical remission (PR) of type 1 diabetes, an accurate definition of PR remains problematic. Two recent studies in children with new-onset T1D demonstrated serious limitations of the present gold standard definition of PR, a stimulated C-peptide (SCP) concentration of >300 pmol/L. The first study employed the concept of insulin sensitivity score (ISS) to show that 55% of subjects with new-onset T1D and a detectable SCP level of >300 pmol/L had low insulin sensitivity (IS) and thus might not be in remission when assessed by insulin-dose adjusted A1c (IDAA1c), an acceptable clinical marker of PR. The second study, a randomized controlled trial of vitamin D (ergocalciferol) administration in children and adolescents with new-onset T1D, demonstrated no significant difference in SCP between the ergocalciferol and placebo groups, but showed a significant blunting of the temporal trend in both A1c and IDAA1c in the ergocalciferol group. These two recent studies indicate the poor specificity and sensitivity of SCP to adequately characterize PR and thus call for a re-examination of current approaches to the definition of PR. They demonstrate the limited sensitivity of SCP, a static biochemical test, to detect the complex physiological changes that occur during PR such as changes in insulin sensitivity, insulin requirements, body weight, and physical activity. These shortcomings call for a broader definition of PR using a combination of functional markers such as IDAA1c and ISS to provide a valid assessment of PR that reaches beyond the static changes in SCP alone.

Difference in Insulin Resistance Assessment between European Union and Non-European Union Obesity Treatment Centers (ESPE Obesity Working Group Insulin Resistance Project)

INTRODUCTION

The obesity epidemic has become one of the most important public health issues of modern times. Impaired insulin sensitivity seems to be the cornerstone of multiple obesity related comorbidities. However, there is no accepted definition of impaired insulin sensitivity.

OBJECTIVE

We hypothesize that assessment of insulin resistance differs between centers.

METHODS

The ESPE Obesity Working Group (ESPE ObWG) Scientific Committee developed a questionnaire with a focus on the routine practices of assessment of hyperinsulinemia and insulin resistance, which was distributed through Google Docs platform to the clinicians and researchers from the current ESPE ObWG database (n = 73). Sixty-one complete responses (84% response rate) from clinicians and researchers were analyzed: 32 from European Union (EU) centers (representatives of 14 countries) and 29 from Non-EU centers (representatives from 10 countries). Standard statistics were used for the data analysis.

RESULTS

The majority of respondents considered insulin resistance (IR) as a clinical tool (85.2%) rather than a research instrument. For the purpose of IR assessment EU specialists prefer analysis of the oral glucose tolerance test (OGTT) results, whereas non-EU ones mainly use Homeostatic Model Assessment of Insulin Resistance (HOMA-IR; p = 0.032). There was no exact cutoff for the HOMA-IR in either EU or non-EU centers. A variety of OGTT time points and substances measured per local protocol were reported. Clinicians normally analyzed blood glucose (88.52% of centers) and insulin (67.21%, mainly in EU centers, p = 0.0051). Furthermore, most participants (70.5%) considered OGTT insulin levels as a more sensitive parameter of IR than glucose. Meanwhile, approximately two-thirds (63.9%) of the centers did not use any cutoffs for the insulin response to the glucose load.

CONCLUSIONS

Since there is no standard for the IR evaluation and uniform accepted indication of performing, an OGTT the assessment of insulin sensitivity varies between EU and non-EU centers. A widely accepted standardized protocol is needed to allow comparison between centers.

Measurement of Peak C-Peptide at Diagnosis Informs Glycemic Control but not Hypoglycemia in Adults With Type 1 Diabetes

Context

High-residual C-peptide in longer-duration type 1 diabetes (T1D) is associated with fewer hypoglycemic events and reduced glycemic variability. Little is known about the impact of C-peptide close to diagnosis.

Objective

Using continuous glucose monitoring (CGM) data from a study of newly diagnosed adults with T1D, we aimed to explore if variation in C-peptide close to diagnosis influenced glycemic variability and risk of hypoglycemia.

Methods

We studied newly diagnosed adults with T1D who wore a Dexcom G4 CGM for 7 days as part of the Exercise in Type 1 Diabetes (EXTOD) study. We examined the relationship between peak stimulated C-peptide and glycemic metrics of variability and hypoglycemia for 36 CGM traces from 23 participants.

Results

For every 100 pmol/L-increase in peak C-peptide, the percentage of time spent in the range 3.9 to 10 mmol/L increased by 2.4% (95% CI, 0.5-4.3), P = .01) with a reduction in time spent at level 1 hyperglycemia (> 10 mmol/L) and level 2 hyperglycemia (> 13.9 mmol/L) by 2.6% (95% CI, –4.9 to –0.4, P = .02) and 1.3% (95% CI, –2.7 to –0.006, P = .04), respectively. Glucose levels were on average lower by 0.19 mmol/L (95% CI, –0.4 to 0.02, P = .06) and SD reduced by 0.14 (95% CI, –0.3 to –0.02, P = .02). Hypoglycemia was not common in this group and no association was observed between time spent in hypoglycemia (P = .97) or hypoglycemic risk (P = .72). There was no association between peak C-peptide and insulin dose–adjusted glycated hemoglobin A_1c (P = .45).

Conclusion

C-peptide is associated with time spent in the normal glucose range and with less hyperglycemia, but not risk of hypoglycemia in newly diagnosed people with T1D.

Type 1 diabetes can present before the age of 6 months and is characterised by autoimmunity and rapid loss of beta cells

AIMS/HYPOTHESIS

Diabetes diagnosed at <6 months of age is usually monogenic. However, 10-15% of affected infants do not have a pathogenic variant in one of the 26 known neonatal diabetes genes. We characterised infants diagnosed at <6 months of age without a pathogenic variant to assess whether polygenic type 1 diabetes could arise at early ages.

METHODS

We studied 166 infants diagnosed with type 1 diabetes at <6 months of age in whom pathogenic variants in all 26 known genes had been excluded and compared them with infants with monogenic neonatal diabetes (n = 164) or children with type 1 diabetes diagnosed at 6-24 months of age (n = 152). We assessed the type 1 diabetes genetic risk score (T1D-GRS), islet autoantibodies, C-peptide and clinical features.

RESULTS

We found an excess of infants with high T1D-GRS: 38% (63/166) had a T1D-GRS >95th centile of healthy individuals, whereas 5% (8/166) would be expected if all were monogenic (p < 0.0001). Individuals with a high T1D-GRS had a similar rate of autoantibody positivity to that seen in individuals with type 1 diabetes diagnosed at 6-24 months of age (41% vs 58%, p = 0.2), and had markedly reduced C-peptide levels (median <3 pmol/l within 1 year of diagnosis), reflecting rapid loss of insulin secretion. These individuals also had reduced birthweights (median z score -0.89), which were lowest in those diagnosed with type 1 diabetes at <3 months of age (median z score -1.98).

CONCLUSIONS/INTERPRETATION

We provide strong evidence that type 1 diabetes can present before the age of 6 months based on individuals with this extremely early-onset diabetes subtype having the classic features of childhood type 1 diabetes: high genetic risk, autoimmunity and rapid beta cell loss. The early-onset association with reduced birthweight raises the possibility that for some individuals there was reduced insulin secretion in utero. Comprehensive genetic testing for all neonatal diabetes genes remains essential for all individuals diagnosed with diabetes at <6 months of age. Graphical abstract.

Detection of intact insulin analogues in post-mortem vitreous humour-Application to forensic toxicology casework

The application of proteomic techniques to forensic science widens the range of analytical capabilities available to forensic laboratories when answering complex toxicology problems. Currently, these techniques are underutilised in post-mortem toxicology because of the historic focus on smaller (<1,000 amu) drug molecules. Definitive confirmation of an insulin overdose by analysis of post-mortem biological matrices is rare and challenging, however can assist coronial investigations pertaining to accidental or intentional overdoses in both diabetic and nondiabetic populations. A semiautomated micro-solid phase extraction paired with mass spectrometry-based insulin methodology was developed and validated for routine use in a Forensic Coronial Toxicology Laboratory. This resulting work reports the first Australian cases where synthetic insulins were confirmed by mass spectrometry in the vitreous humour of Type 1 diabetics who intentionally or accidentally overdosed on their prescription medication glargine and aspart. The detection of glargine M1 in Case 1, aspart in Case 2 and glargine M1 was indicated in Case 3. This paper highlights advancements in forensic coronial toxicology and the promising potential of proteomic analysis in a forensic context.

Hyperinsulinaemia in cancer

Elevated circulating insulin levels are frequently observed in the setting of obesity and early type 2 diabetes, as a result of insensitivity of metabolic tissues to the effects of insulin. Higher levels of circulating insulin have been associated with increased cancer risk and progression in epidemiology studies. Elevated circulating insulin is believed to be a major factor linking obesity, diabetes and cancer. With the development of targeted cancer therapies, insulin signalling has emerged as a mechanism of therapeutic resistance. Although metabolic tissues become insensitive to insulin in the setting of obesity, a number of mechanisms allow cancer cells to maintain their ability to respond to insulin. Significant progress has been made in the past decade in understanding the insulin receptor and its signalling pathways in cancer, and a number of lessons have been learnt from therapeutic failures. These discoveries have led to numerous clinical trials that have aimed to reduce the levels of circulating insulin and to abrogate insulin signalling in cancer cells. With the rising prevalence of obesity and diabetes worldwide, and the realization that hyperinsulinaemia may contribute to therapeutic failures, it is essential to understand how insulin and insulin receptor signalling promote cancer progression.

A simple formula to correct for the effects of storage time and temperature on the insulin concentration

OBJECTIVE

To investigate the influence of storage time and temperature on plasma insulin levels and to establish a correction formula.

METHODS

Venous blood samples were taken from 20 volunteers and processed as follows: whole blood samples, centrifuged samples, and separated plasma samples were stored at 4°C or 25°C. Insulin levels were determined by direct chemiluminescence at 0, 0.5, 1, 2, 4, and 8 hours. According to the correlation between the insulin concentration ratio and storage time, correction formulas for the insulin concentration were established. To verify the test, the venous blood samples of another 33 volunteers were processed in the same way. The insulin levels of the samples were corrected after 3, 6, 12, and 24 hours and compared with the value at 0 hours to verify the feasibility of the corrected formula.

RESULTS

With the prolongation of storage time, the insulin levels of the whole blood samples at 4°C or 25°C and of the centrifuged samples at 25°C decreased gradually (P < .001), and the insulin level correction formulas were Ccorrection  = Cdetermination /0.991e-0.069 x , Ccorrection  = Cdetermination /1.048e-0.126 x , and Ccorrection  = Cdetermination /[-0.068ln(x) + 0.9242]. There was no significant difference between the corrected insulin results and the original results at any time within 12 hours (P > .05).

CONCLUSIONS

The insulin levels of the whole blood samples at 4°C or 25°C and of the plasma samples at 25°C gradually decreased with storage time. The effect of storage time on the insulin level can be reduced with the correction formulas.

Beta-cell failure in type 2 diabetes: mechanisms, markers, and clinical implications

It is well known that type 2 diabetes mellitus (T2D) is a globally increasing health burden. Despite recent therapeutic advances and the availability of many different classes of antihyperglycemic therapy, a large proportion of people do not achieve glycemic control. A decline in pancreatic beta-cell function has been defined as a key contributing factor to progression of T2D. In fact, a significant proportion of beta-cell secretory capacity is thought to be lost well before the diagnosis of T2D is made. Several models have been proposed to explain the reduction in beta-cell function, including reduced beta-cell number, beta-cell exhaustion, and dedifferentiation or transdifferentiation into other cell types. However, there have been reports that suggest remission of T2D is possible, and it is believed that beta-cell dysfunction may be, in part, reversible. As such, the question of whether beta cells are committed to failure in people with T2D is complex. It is now widely accepted that early restoration of normoglycemia may protect beta-cell function. Key to the successful implementation of this approach in clinical practice is the appropriate assessment of individuals at risk of beta-cell failure, and the early implementation of appropriate treatment options. In this review, we discuss the progression of T2D in the context of beta-cell failure and describe how C-peptide testing can be used to assess beta-cell function in primary care practice. In conclusion, significant beta-cell dysfunction is likely in individuals with certain clinical characteristics of T2D, such as long duration of disease, high glycated hemoglobin (≥9%), and/or long-term use of therapies that continuously stimulate the beta cell. In these people, measurement of beta-cell status could assist with choice of appropriate therapy to delay or potentially reverse beta-cell dysfunction and the progression of T2D.

Immunoreactive insulin stability in horses at risk of insulin dysregulation

Background

Diseases associated with insulin dysregulation (ID), such as equine metabolic syndrome and pituitary pars intermedia dysfunction, are of interest to practitioners because of their association with laminitis. Accurate insulin concentration assessment is critical in diagnosing and managing these diseases.

Hypothesis/Objectives

To determine the effect of time, temperature, and collection tube type on insulin concentrations in horses at risk of ID.

Animals

Eight adult horses with body condition score >6/9.

Methods

In this prospective study, subjects underwent an infeed oral glucose test 2 hours before blood collection. Blood samples were divided into ethylenediaminetetraacetic acid, heparinized, or serum tubes and stored at 4 or 20°C. Tubes were centrifuged and analyzed for insulin by a chemiluminescent assay over 8 days. Changes in insulin concentrations were compared with a linear mixed effects model.

Results

An overall effect of time, tube type and temperature was identified (P = .01, P = 0.001, and P = 0.001, respectively). Serum and heparinized samples had similar concentrations for 3 days at 20°C and 8 days at 4°C; however, after 3 days at 20°C, heparinized samples had significantly higher insulin concentrations (P = .004, P = .03, and P = .03 on consecutive days). Ethylenediaminetetraacetic acid samples had significantly lower insulin concentrations regardless of time and temperature (P = .001 for all comparisons).

Conclusions and Clinical Importance

These results suggest an ideal protocol to determine insulin concentrations involves using serum or heparinized samples with analysis occurring within 3 days at 20°C or 8 days at 4°C.

Stability of urinary albumin and creatinine after 12 months storage at -20 °C and -80 °C

Background

Increasing albumin to creatinine ratio (ACR) within the normal range is a risk factor for cardiovascular disease in the general population. Clinical and epidemiological studies often store urine samples for long durations prior to ACR assessment. The stability of ACR at the lowest urinary albumin concentrations during prolonged storage has not been previously studied because routine clinical assays can’t quantify very low concentrations of albumin.

Aim

To determine the stability of urinary albumin and creatinine over 12 months in samples stored at −20 °C and −80 °C using an assay which enables assessment of previously undetectable levels of albumin and to investigate if additives can be used to prevent urinary albumin degradation.

Method

ACR was measured in 30 urine samples from healthy subjects on the day of collection. Each sample was divided into 5 portions, each receiving a different treatment; alkalisation, protease inhibiter, boric acid, low protein binding tubes and no treatment (control). Samples were stored at −20 °C and −80 °C and ACR was analysed again after 12 months.

Results

Mean (95% CI) percent change in ACR was −34.3% (−47.2 to −21.4; p < 0.0001) and −1.8% (−9.4 to 5.8; p = 0.91) in samples stored at −20 °C and −80 °C respectively. Treating samples did not prevent the reduction in albumin at −20 °C (p < 0.001).

Conclusion

The loss in urinary albumin concentration which occurs during storage at −20 °C for 12 months is not prevented by pre-treating samples prior to storage. For accurate determination of albumin concentration or ACR, samples should be stored at −80 °C on day of collection.

•

Urine samples should be stored at −80 °C on day of collection to prevent loss of albumin.

•

ACR is reduced by over 30% in samples stored at −20 °C for 12 months.

•

Treating samples prior to storage at −20 °C does not prevent loss in urinary albumin.

C-Peptide Decline in Type 1 Diabetes Has Two Phases: An Initial Exponential Fall and a Subsequent Stable Phase

OBJECTIVE

The decline in C-peptide in the 5 years after diagnosis of type 1 diabetes has been well studied, but little is known about the longer-term trajectory. We aimed to examine the association between log-transformed C-peptide levels and the duration of diabetes up to 40 years after diagnosis.

RESEARCH DESIGN AND METHODS

We assessed the pattern of association between urinary C-peptide/creatinine ratio (UCPCR) and duration of diabetes in cross-sectional data from 1,549 individuals with type 1 diabetes using nonlinear regression approaches. Findings were replicated in longitudinal follow-up data for both UCPCR (n = 161 individuals, 326 observations) and plasma C-peptide (n = 93 individuals, 473 observations).

RESULTS

We identified two clear phases of C-peptide decline: an initial exponential fall over 7 years (47% decrease/year [95% CI -51, -43]) followed by a stable period thereafter (+0.07%/year [-1.3, +1.5]). The two phases had similar durations and slopes in patients above and below the median age at diagnosis (10.8 years), although levels were lower in the younger patients irrespective of duration. Patterns were consistent in both longitudinal UCPCR (n = 162; ≤7 years duration: -48%/year [-55, -38]; >7 years duration -0.1% [-4.1, +3.9]) and plasma C-peptide (n = 93; >7 years duration only: -2.6% [-6.7, +1.5]).

CONCLUSIONS

These data support two clear phases of C-peptide decline: an initial exponential fall over a 7-year period, followed by a prolonged stabilization where C-peptide levels no longer decline. Understanding the pathophysiological and immunological differences between these two phases will give crucial insights into understanding β-cell survival.

Random non-fasting C-peptide testing can identify patients with insulin-treated type 2 diabetes at high risk of hypoglycaemia

AIMS/HYPOTHESIS

The aim of this study was to determine whether random non-fasting C-peptide (rCP) measurement can be used to assess hypoglycaemia risk in insulin-treated type 2 diabetes.

METHODS

We compared continuous glucose monitoring-assessed SD of blood glucose and hypoglycaemia duration in 17 patients with insulin-treated type 2 diabetes and severe insulin deficiency (rCP < 200 pmol/l) and 17 matched insulin-treated control patients with type 2 diabetes but who had preserved endogenous insulin (rCP > 600 pmol/l). We then assessed the relationship between rCP and questionnaire-based measures of hypoglycaemia in 256 patients with insulin-treated type 2 diabetes and a comparison group of 209 individuals with type 1 diabetes.

RESULTS

Continuous glucose monitoring (CGM)-assessed glucose variability and hypoglycaemia was greater in individuals with rCP < 200 pmol/l despite similar mean glucose. In those with low vs high C-peptide, SD of glucose was 4.2 (95% CI 3.7, 4.6) vs 3.0 (2.6, 3.4) mmol/l (p < 0.001). In the low-C-peptide vs high-C-peptide group, the proportion of individuals experiencing sustained hypoglycaemia ≤ 4 mmol/l was 94% vs 41% (p < 0.001), the mean rate of hypoglycaemia was 5.5 (4.4, 6.7) vs 2.1 (1.4, 2.9) episodes per person per week (p = 0.004) and the mean duration was 630 (619, 643) vs 223 (216, 230) min per person per week (p = 0.01). Hypoglycaemia ≤ 3 mmol/l was infrequent in individuals with preserved C-peptide (1.8 [1.2, 2.6] episodes per person per week vs 0.4 [0.1, 0.8] episodes per person per week for low vs high C-peptide, p = 0.04) and only occurred at night. In a population-based cohort with insulin-treated type 2 diabetes, self-reported hypoglycaemia was twice as frequent in those with rCP < 200 pmol/l (OR 2.0, p < 0.001) and the rate of episodes resulting in loss of consciousness or seizure was five times higher (OR 5.0, p = 0.001). The relationship between self-reported hypoglycaemia and C-peptide was similar in individuals with type 1 and type 2 diabetes.

CONCLUSIONS/INTERPRETATION

Low rCP is associated with increased glucose variability and hypoglycaemia in patients with insulin-treated type 2 diabetes and represents a practical, stable and inexpensive biomarker for assessment of hypoglycaemia risk.

Exercise to preserve β-cell function in recent-onset Type 1 diabetes mellitus (EXTOD) - a randomized controlled pilot trial

AIM

Residual β-cell function is present at the time of diagnosis with Type 1 diabetes. Preserving this β-cell function reduces complications. We hypothesized that exercise preserves β-cell function in Type 1 diabetes and undertook a pilot trial to address the key uncertainties in designing a definitive trial to test this hypothesis.

METHODS

A randomized controlled pilot trial in adults aged 16-60 years diagnosed with Type 1 diabetes within the previous 3 months was undertaken. Participants were assigned to control (usual care) or intervention (exercise consultation every month), in a 1 : 1 ratio for 12 months. The primary outcomes were recruitment rate, drop out, exercise adherence [weeks with ≥ 150 min of self-reported moderate to vigorous physical activity (MVPA)], and exercise uptake in the control group. The secondary outcomes were differences in insulin sensitivity and rate of loss of β-cell function between intervention and control at 6 and 12 months.

RESULTS

Of 507 individuals who were approached, 58 (28 control, 30 intervention) entered the study and 41 completed it. Participants were largely white European males, BMI 24.8 ± 3.8 kg/m² , HbA_1c 75 ± 25 mmol/mol (9 ± 2%). Mean level of objectively measured MVPA increased in the intervention group (mean 243 to 273 min/week) and 61% of intervention participants reached the target of ≥ 150 min/week of self-reported MVPA on at least 42 weeks of the year. Physical activity levels fell slightly in the control group (mean 277 to 235 min of MVPA/week). There was exploratory evidence that intervention group became more insulin sensitive and required less insulin. However, the rate of loss of β-cell function appeared similar between the groups, although the change in insulin sensitivity may have affected this.

CONCLUSION

We show that it is possible to recruit and randomize people with newly diagnosed Type 1 diabetes to a trial of an exercise intervention, and increase and maintain their exercise levels for 12 months. Future trials need to incorporate measures of greater adherence to exercise training targets, and include more appropriate measures of β-cell function. (Clinical Trials Registry No; ISRCTN91388505).

A Practical Review of C-Peptide Testing in Diabetes

C-peptide is a widely used measure of pancreatic beta cell function. It is produced in equimolar amounts to endogenous insulin but is excreted at a more constant rate over a longer time. Methods of estimation include urinary and unstimulated and stimulated serum sampling. Modern assays detect levels of c-peptide which can be used to guide diabetes diagnosis and management. We explore the evidence behind the various tests available. We recommend the glucagon stimulation c-peptide testing owing to its balance of sensitivity and practicality. C-peptide levels are associated with diabetes type and duration of disease. Specifically a c-peptide level of less than 0.2 nmol/l is associated with a diagnosis of type 1 diabetes mellitus (T1DM). C-peptide level may correlate with microvascular and macrovascular complications and future use of insulin therapy, as well as likely response to other individual therapies. We explore the potential uses of c-peptide measurement in clinical practice.

Proinsulin is stable at room temperature for 24 hours in EDTA: A clinical laboratory analysis (adAPT 3)

Aims

Reference laboratories advise immediate separation and freezing of samples for the assay of proinsulin, which limit its practicability for smaller centres. Following the demonstration that insulin and C-peptide are stable in EDTA at room temperature for at least 24hours, we undertook simple stability studies to establish whether the same might apply to proinsulin.

Methods

Venous blood samples were drawn from six adult women, some fasting, some not, aliquoted and assayed immediately and after storage at either 4°C or ambient temperature for periods from 2h to 24h.

Results

There was no significant variation or difference with storage time or storage condition in either individual or group analysis.

Conclusion

Proinsulin appears to be stable at room temperature in EDTA for at least 24h. Immediate separation and storage on ice of samples for proinsulin assay is not necessary, which will simplify sample transport, particularly for multicentre trials.

Current laboratory requirements for adrenocorticotropic hormone and renin/aldosterone sample handling are unnecessarily restrictive

Samples for adrenocorticotropic hormone (ACTH) and aldosterone/renin analysis usually require rapid transport to the receiving laboratory for immediate separation and freezing. In practice, this means assessment is limited to hospital settings and many samples are rejected. We examined whether these requirements are necessary by assessing the stability of ACTH, aldosterone and renin over 48 hours in whole blood collected in serum gel and EDTA plasma from 31 participants. Our results show that ACTH collected into EDTA plasma is stable at room temperature for at least 6 hours, mean change at 6 hours -2.6% (95% CI -9.7 to 4.5). Both aldosterone and renin were stable collected on serum gel at room temperature for at least 6 hours: mean change aldosterone +0.2% (95% CI -3.6 to 4.0), renin -1.9% (95% CI -7.0 to3.2). Therefore, by using appropriate preservatives, ACTH and aldosterone/renin can be measured on samples collected at room temperature and processed within 6 hours. This would facilitate outpatient and emergency room assessment of these analytes.

Random non-fasting C-peptide: bringing robust assessment of endogenous insulin secretion to the clinic

BACKGROUND

Measuring endogenous insulin secretion using C-peptide can assist diabetes management, but standard stimulation tests are impractical for clinical use. Random non-fasting C-peptide assessment would allow testing when a patient is seen in clinic.

METHODS

We compared C-peptide at 90 min in the mixed meal tolerance test (sCP) with random non-fasting blood C-peptide (rCP) and random non-fasting urine C-peptide creatinine ratio (rUCPCR) in 41 participants with insulin-treated diabetes [median age 72 (interquartile range 68-78); diabetes duration 21 (14-31) years]. We assessed sensitivity and specificity for previously reported optimal mixed meal test thresholds for severe insulin deficiency (sCP < 200 pmol//l) and Type 1 diabetes/inability to withdraw insulin (< 600 pmol//l), and assessed the impact of concurrent glucose.

RESULTS

rCP and sCP levels were similar (median 546 and 487 pmol//l, P = 0.92). rCP was highly correlated with sCP, r = 0.91, P < 0.0001, improving to r = 0.96 when excluding samples with concurrent glucose < 8 mmol//l. An rCP cut-off of 200 pmol//l gave 100% sensitivity and 93% specificity for detecting severe insulin deficiency, with area under the receiver operating characteristic curve of 0.99. rCP < 600 pmol//l gave 87% sensitivity and 83% specificity to detect sCP < 600 pmol//l. Specificity improved to 100% when excluding samples with concurrent glucose < 8 mmol//l. rUCPCR (0.52 nmol/mmol) was also well-correlated with sCP, r = 0.82, P < 0.0001. A rUCPCR cut-off of < 0.2 nmol/ mmol gave sensitivity and specificity of 83% and 93% to detect severe insulin deficiency, with area under the receiver operating characteristic curve of 0.98.

CONCLUSIONS

Random non-fasting C-peptide measures are strongly correlated with mixed meal C-peptide, and have high sensitivity and specificity for identifying clinically relevant thresholds. These tests allow assessment of C-peptide at the point patients are seen for clinical care.

Promoter optimisation of lentiviral vectors for efficient insulin gene expression in canine mesenchymal stromal cells: potential surrogate beta cells

BACKGROUND

The lack of an ideal cell type that can be easily acquired, modified to produce insulin, and re-implanted has been a limitation for ex vivo insulin gene therapy. Canine diabetes is currently treated with human insulin and is a good model for human diabetes. Mesenchymal stromal cells (MSCs) are a promising candidate cell type for gene therapy. In the present study, we optimised insulin production using lentiviral transduced canine MSCs (cMSCs), aiming to evaluate their ability for use as surrogate beta cells.

METHODS

Canine MSCs were derived from bone marrow and validated by measuring the expression of MSC lineage specific markers. Lentivirus vectors encoding the proinsulin gene (with or without a Kozak sequence) under the control of spleen focus forming virus, cytomegalovirus, elongation factor 1α and simian virus 40 promotors were generated and used to transduce primary cMSCs and a hepatocyte cell line. The insulin-producing capacity of transduced primary cMSCs was assessed by measuring the concentration of C-peptide produced.

RESULTS

Primary cMSC could be readily expanded in culture and efficiently transduced using lentiviral vectors encoding proinsulin. Increasing the multiplicity of infection from 3 to 20 led to an increase in C-peptide secretion (from 1700 to 4000 pmol/l). The spleen focus forming virus promoter conferred the strongest transcriptional ability.

CONCLUSIONS

The results of the present study suggest that optimised lentiviral transduction of the insulin gene into primary cMSCs renders these cells capable of secreting insulin over both the short- and long-term, in sufficient quantities in vitro to support their potential use in insulin gene therapy.

Detection of C-Peptide in Urine as a Measure of Ongoing Beta Cell Function

C-peptide is a protein secreted by the pancreatic beta cells in equimolar quantities with insulin, following the cleavage of proinsulin into insulin. Measurement of C-peptide is used as a surrogate marker of endogenous insulin secretory capacity. Assessing C-peptide levels can be useful in classifying the subtype of diabetes as well as assessing potential treatment choices in the management of diabetes.Standard measures of C-peptide involve blood samples collected either fasted or, most often, after a fixed stimulus (such as oral glucose, mixed meal, or IV glucagon). Despite the established clinical utility of blood C-peptide measurement, its widespread use is limited. In many instances this is due to perceived practical restrictions associated with sample collection.Urine C-peptide measurement is an attractive noninvasive alternative to blood measures of beta-cell function. Urine C-peptide creatinine ratio measured in a single post stimulated sample has been shown to be a robust, reproducible measure of endogenous C-peptide which is stable for three days at room temperature when collected in boric acid. Modern high sensitivity immunoassay technologies have facilitated measurement of C-peptide down to single picomolar concentrations.

Degradation and Stabilization of Peptide Hormones in Human Blood Specimens

Plasma hormone peptides, including GLP-1, GIP, Glucagon, and OXM, possess multiple physiological roles and potential therapeutic and diagnostic utility as biomarkers in the research of metabolic disorders. These peptides are subject to proteolytic degradation causing preanalytical variations. Stabilization for accurate quantitation of these active peptides in ex vivo blood specimens is essential for drug and biomarker development. We investigated the protease-driven instability of these peptides in conventional serum, plasma, anticoagulated whole blood, as well as whole blood and plasma stabilized with protease inhibitors. The peptide was monitored by both time-course Matrix-Assisted Laser Desorption Ionization Time-to-Flight Mass Spectrometry (MALDI –TOF MS) and Ab-based assay (ELISA or RIA). MS enabled the identification of proteolytic fragments. In non-stabilized blood samples, the results clearly indicated that dipeptidyl peptidase-IV (DPP-IV) removed the N-terminal two amino acid residues from GLP-1, GIP and OXM(1-37) and not-yet identified peptidase(s) cleave(s) the full-length OXM(1-37) and its fragments. DPP-IV also continued to remove two additional N-terminal residues of processed OXM(3–37) to yield OXM(5–37). Importantly, both DPP-IV and other peptidase(s) activities were inhibited efficiently by the protease inhibitors included in the BD P800* tube. There was preservation of GLP-1, GIP, OXM and glucagon in the P800 plasma samples with half-lives > 96, 96, 72, and 45 hours at room temperature (RT), respectively. In the BD P700* plasma samples, the stabilization of GLP-1 was also achieved with half-life > 96 hours at RT. The stabilization of these variable peptides increased their utility in drug and/or biomarker development. While stability results of GLP-1 obtained with Ab-based assay were consistent with those obtained by MS analysis, the Ab-based results of GIP, Glucagon, and OXM did not reflect the time-dependent degradations revealed by MS analysis. Therefore, we recommended characterizing the degradation of the peptide using the MS-based method when investigating the stability of a specific peptide.

Similarity of Serum and Plasma Insulin-like Growth Factor Concentrations

BACKGROUND

Insulin-like growth factors (IGFs) are implicated in many normal physiological processes and pathological states, including cancer. For large consortia projects, it may be necessary to make comparisons among studies with different specimens that were not collected specifically to optimize the measurement of IGFs.

OBJECTIVE

This study aimed to compare IGFs in matched serum and plasma samples.

METHODS

We measured IGF-I, IGF-II, insulin-like growth factor-binding protein (IGFBP)-3, C-peptide, and leptin in serum and ethylenediaminetetraacetic–containing-plasma samples obtained concurrently from 30 healthy women aged 64–80 years in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial using chemiluminescent or colorimetric enzyme-linked immune assays. Coefficients of variation (CVs) and correlations were determined.

RESULTS

Intraassay CVs ranged from 0.4% for IGFBP-3 to 10% for IGF-II. Mean concentrations of all analytes were higher in the serum, but the differences in mean concentrations of the analytes between serum and plasma were all <11%. Concordance correlation coefficients of matched serum/plasma specimens were 0.92, 0.91, 0.82, 0.96, and 0.99 for IGF-I, IGFBP-3, IGF-II, C-peptide, and leptin, respectively.

CONCLUSION

IGF concentrations measured in serum and plasma are highly correlated but are consistently slightly higher in serum, suggesting that IGF values should be corrected for systematic bias, particularly in consortial efforts when pooling data derived from different specimens.

Pregnancy glycaemia and cord-blood levels of insulin and leptin in Pakistani and white British mother-offspring pairs: findings from a prospective pregnancy cohort

AIMS/HYPOTHESIS

To determine the extent to which gestational fasting and postload levels of glucose explain differences in infant fat mass between UK-born Pakistani and white British infants.

METHODS

Analyses were undertaken in a prospective pregnancy cohort study of 1,415 women and their singleton live-born infants (629 white British and 786 Pakistani). Infant fat mass was assessed by cord-blood leptin levels and fetal insulin secretion by cord-blood insulin levels. Maternal OGTTs were completed at 26-28 weeks of gestation.

RESULTS

Pakistani women had higher fasting and postload glucose levels and greater incidence of gestational diabetes than white British women. Higher fasting and postload glucose levels were associated with higher cord-blood levels of insulin and leptin in all participants, irrespective of ethnicity. Cord-blood leptin levels were 16% (95% CI 6, 26) higher in Pakistani than in white British infants. After adjustment for fasting glucose levels, this difference attenuated to 7% (-3, 16), and with additional adjustment for cord-blood insulin levels it attenuated further to 5% (-4, 14). Path analyses supported the hypothesis that fasting glucose levels mediate the relationship of Pakistani ethnicity to greater fat mass at birth, as measured by cord-blood leptin levels; on average, 19% of this mediation involved fetal insulin secretion. Postload glucose levels did not act as an important mediator of ethnic differences in cord-blood leptin levels. Results were very similar when 130 women with gestational diabetes were removed.

CONCLUSIONS/INTERPRETATION

These novel findings suggest a role of maternal pregnancy glycaemia in mediating differences in fat mass between Pakistani and white British infants.

Urine C-peptide creatinine ratio can be used to assess insulin resistance and insulin production in people without diabetes: an observational study

OBJECTIVES

The current assessment of insulin resistance (IR) in epidemiology studies relies on the blood measurement of C-peptide or insulin. A urine C-peptide creatinine ratio (UCPCR) can be posted from home unaided. It is validated against serum measures of the insulin in people with diabetes. We tested whether UCPCR could be a surrogate measure of IR by examining the correlation of UCPCR with serum insulin, C-peptide and HOMA2 (Homeostasis Model Assessment 2)-IR in participants without diabetes and with chronic kidney disease (CKD).

DESIGN

Observational study.

SETTING

Single-centre clinical research facility.

PARTICIPANTS

37 healthy volunteers and 30 patients with CKD (glomerular filtration rate 15-60) were recruited.

PRIMARY AND SECONDARY ENDPOINTS

Serum insulin, C-peptide and glucose at fasting (0), 30, 60, 90 and 120 min were measured during an oral glucose tolerance test (OGTT). Second-void fasting UCPCR and 120 min post-OGTT UCPCR were collected. HOMA2-IR was calculated using fasting insulin and glucose. The associations between UCPCR and serum measures were assessed using Spearman's correlations.

RESULTS

In healthy volunteers, fasting second-void UCPCR strongly correlated with serum insulin (rs=0.69, p<0.0001), C-peptide (rs=0.73, p<0.0001) and HOMA2-IR (rs=-0.69, p<0.0001). 120 min post-OGTT UCPCR correlated strongly with C-peptide and insulin area under the curve. In patients with CKD, UCPCR did not correlate with serum C-peptide, insulin or HOMA2-IR.

CONCLUSIONS

In participants with normal renal function, UCPCR may be a simple, practical method for the assessment of IR in epidemiology studies.

Urinary C-peptide creatinine ratio detects absolute insulin deficiency in Type 2 diabetes

AIMS

To determine the prevalence and clinical characteristics of absolute insulin deficiency in long-standing Type 2 diabetes, using a strategy based on home urinary C-peptide creatinine ratio measurement.

METHODS

We assessed the urinary C-peptide creatinine ratios, from urine samples taken at home 2 h after the largest meal of the day, in 191 insulin-treated subjects with Type 2 diabetes (diagnosis age ≥45 years, no insulin in the first year). If the initial urinary C-peptide creatinine ratio was ≤0.2 nmol/mmol (representing absolute insulin deficiency), the assessment was repeated. A standardized mixed-meal tolerance test with 90-min stimulated serum C-peptide measurement was performed in nine subjects with a urinary C-peptide creatinine ratio ≤ 0.2 nmol/mmol (and in nine controls with a urinary C-peptide creatinine ratio >0.2 nmol/mmol) to confirm absolute insulin deficiency.

RESULTS

A total of 2.7% of participants had absolute insulin deficiency confirmed by a mixed-meal tolerance test. They were identified initially using urinary C-peptide creatinine ratio: 11/191 subjects (5.8%) had two consistent urinary C-peptide creatinine ratios ≤ 0.2 nmol/mmol; 9 of these 11 subjects completed a mixed-meal tolerance test and had a median stimulated serum C-peptide of 0.18 nmol/l. Five of these 9 had stimulated serum C-peptide <0.2 nmol/l and 9/9 subjects with urinary C-peptide creatinine ratio >0.2 had endogenous insulin secretion confirmed by the mixed-meal tolerance test. Compared with subjects with a urinary C-peptide creatinine ratio >0.2 nmol/mmol, those with confirmed absolute insulin deficiency had a shorter time to insulin treatment (median 2.5 vs. 6 years, P=0.005) and lower BMI (25.1 vs. 29.1 kg/m(2) , P=0.04). Two out of the five patients with absolute insulin deficiency were glutamic acid decarboxylase autoantibody-positive.

CONCLUSIONS

Absolute insulin deficiency may occur in long-standing Type 2 diabetes, and cannot be reliably predicted by clinical features or autoantibodies. Absolute insulin deficiency in Type 2 diabetes may increase the risk of hypoglycaemia and ketoacidosis, as in Type 1 diabetes. Its recognition should help guide treatment, education and management. The urinary C-peptide creatinine ratio is a practical non-invasive method to aid detection of absolute insulin deficiency, with a urinary C-peptide creatinine ratio > 0.2 nmol/mmol being a reliable indicator of retained endogenous insulin secretion.

The clinical utility of C-peptide measurement in the care of patients with diabetes

C-peptide is produced in equal amounts to insulin and is the best measure of endogenous insulin secretion in patients with diabetes. Measurement of insulin secretion using C-peptide can be helpful in clinical practice: differences in insulin secretion are fundamental to the different treatment requirements of Type 1 and Type 2 diabetes. This article reviews the use of C-peptide measurement in the clinical management of patients with diabetes, including the interpretation and choice of C-peptide test and its use to assist diabetes classification and choice of treatment. We provide recommendations for where C-peptide should be used, choice of test and interpretation of results. With the rising incidence of Type 2 diabetes in younger patients, the discovery of monogenic diabetes and development of new therapies aimed at preserving insulin secretion, the direct measurement of insulin secretion may be increasingly important. Advances in assays have made C-peptide measurement both more reliable and inexpensive. In addition, recent work has demonstrated that C-peptide is more stable in blood than previously suggested or can be reliably measured on a spot urine sample (urine C-peptide:creatinine ratio), facilitating measurement in routine clinical practice. The key current clinical role of C-peptide is to assist classification and management of insulin-treated patients. Utility is greatest after 3-5 years from diagnosis when persistence of substantial insulin secretion suggests Type 2 or monogenic diabetes. Absent C-peptide at any time confirms absolute insulin requirement and the appropriateness of Type 1 diabetes management strategies regardless of apparent aetiology.