Relation between the serum level of C-peptide and risk factors for coronary heart disease and diabetic microangiopathy in patients with type-2 diabetes mellitus

May C-peptide index be a new marker to predict proteinuria in anemic patients with type 2 diabetes mellitus?

OBJECTIVE

C-peptide is a reliable marker of beta cell reserve and is associated with diabetic complications. Furthermore, HbA1c level is associated with micro- and macro-vascular complications in diabetic patients. HbA1c measurement of diabetic patients with anemia may be misleading because HbA1c is calculated in percent by taking reference to hemoglobin measurements. We hypothesized that there may be a relationship between C-peptide index (CPI) and proteinuria in anemic patients with type 2 diabetes mellitus (T2DM). Therefore, the aim of the present study was to investigate the association between C-peptide levels and CPI in anemic patients with T2DM and proteinuria.

METHODS

The patients over 18 years of age with T2DM whose C-peptide levels were analyzed in Endocrinology and Internal medicine clinics between 2014 and 2018 with normal kidney functions (GFR>60 ml/min) and who do not use any insulin secretagogue oral antidiabetic agent (i.e. sulfonylurea) were enrolled into the study.

RESULTS

Hemoglobin levels were present in 342 patients with T2DM. Among these 342 cases, 258 (75.4%) were non-anemic whereas 84 (24.6%) were anemic. The median DM duration of the anemic group was statistically significantly higher in T2DM (p=0.003). There was no statistically significant difference found in proteinuria prevalence between non-anemic and anemic patient groups (p=0.690 and p=0.748, respectively). Anemic T2DM cases were corrected according to the age, gender, and duration of DM. C-peptide and CPI levels were not statistically significant to predict proteinuria (p=0.449 and p=0.465, respectively).

CONCLUSION

The present study sheds light to the association between C-peptide, CPI, and anemic diabetic nephropathy in T2DM patients and indicates that further prospective studies are needed to clarify this issue.

Decreased β-Cell Function is Associated with Cardiovascular Autonomic Neuropathy in Chinese Patients Newly Diagnosed with Type 2 Diabetes

The influence of β-cell function on cardiovascular autonomic neuropathy (CAN), an important diabetes-related complication, is still unclear. In this study, we aimed to investigate the association between residual β-cell function and CAN in patients newly diagnosed with type 2 diabetes. We enrolled 90 newly-diagnosed type 2 diabetic patients and 37 participants with normal glucose tolerance as controls. The patients were divided into a CAN+ group (diabetic patients with CAN, n = 20) and a CAN− group (diabetic patients without CAN, n = 70) according to the standard Ewing battery of tests. Fasting and postprandial plasma glucose, insulin, and C-peptide were measured. Homeostasis model assessment-beta cells (HOMA-B) and HOMA-insulin resistance (IR) were calculated. The prevalence of CAN in this population was 22.2%. Compared with the CAN− group, the CAN+ group had significantly lower fasting plasma insulin (6.60 ± 4.39 vs 10.45 ± 7.82 μ/L, P = 0.029), fasting C-peptide (0.51 ± 0.20 vs 0.82 ± 0.51 nmol/L, P = 0.004), and HOMA-B (21.44 ± 17.06 vs 44.17 ± 38.49, P = 0.002). Fasting C-peptide was correlated with the Valsalva ratio (r = 0.24, P = 0.043) and the 30:15 test (r = 0.26, P = 0.023). Further analysis showed that fasting C-peptide (OR: 0.041, 95% CI 0.003–0.501, P = 0.012) and HOMA-B (OR: 0.965, 95% CI 0.934–0.996, P = 0.028) were independently associated with cardiovascular autonomic nerve function in this population. The patients with fasting C-peptide values < 0.67 nmol/L were more likely to have CAN than those with C-peptide levels ≥0.67 nmol/L (OR: 6.00, 95% CI 1.815–19.830, P = 0.003). A high prevalence of CAN was found in patients with newly-diagnosed type 2 diabetes. Decreased β-cell function was closely associated with CAN in this population.

C-peptide levels and the risk of diabetes and pre-diabetes among Chinese women with gestational diabetes

AIMS

To examine the association of connecting peptide (C-peptide) and the risks of postpartum diabetes and pre-diabetes among women with prior gestational diabetes.

METHODS

A cross-sectional study of 1263 women with prior gestational diabetes was carried out at 1-5years after delivery in Tianjin, China. Logistic regression was used to assess the associations of C-peptide and the risks of diabetes and pre-diabetes.

RESULTS

The multivariable-adjusted odds ratios based on different levels of C-peptide (0-33%, 34-66%, 67-90%, and >90% as C-peptide cutpoints) were 1.00, 1.93 (95% confidence interval [CI] 0.85-4.39), 2.49 (95% CI 1.06-5.87), and 3.88 (95% CI 1.35-11.1) for diabetes (P for trend <0.0001), and 1.00, 1.66 (95% CI 1.18-2.36), 2.38 (95% CI 1.56-3.62) and 2.35 (95% CI 1.27-4.37) for pre-diabetes (P for trend <0.0001), respectively. Restricted cubic splines models showed a positive linear association of C-peptide as a continuous variable with the risks of type 2 diabetes and pre-diabetes. The positive association was significant when stratified by healthy weight and overweight participants.

CONCLUSIONS

We found a positive association between serum C-peptide levels and the risks of diabetes and pre-diabetes among Chinese women with prior gestational diabetes. Our finding suggested that elevated C-peptide levels may be a predictor of diabetes and pre-diabetes.

Relationship between serum C-peptide level and diabetic retinopathy according to estimated glomerular filtration rate in patients with type 2 diabetes

OBJECTIVE

To test the hypothesis that serum C-peptide level would relate to the risk of diabetic retinopathy (DR) in type 2 diabetic patients independently of estimated glomerular filtration rate (eGFR).

DESIGN

A total of 2,062 patients with type 2 diabetes were investigated in this cross-sectional study. Fasting C-peptide, 2-hour postprandial C-peptide, and ΔC-peptide (postprandial C-peptide minus fasting C-peptide) levels were measured. The patients were divided into two groups according to eGFR (ml∙min(-1)1.73m(-2)): patients without renal impairment (eGFR ≥60) and those with renal impairment (eGFR <60).

RESULTS

In subjects both with and without renal impairment, patients with DR showed lower levels of fasting C-peptide, postprandial C-peptide and ΔC-peptide. In multivariate analysis, serum C-peptide levels were significantly associated with DR (odds ratio [OR] of each standard deviation increase in the logarithmic value, 0.85; 95% confidence interval [CI], 0.78-0.92 for fasting C-peptide, P<0.001; OR, 0.87; 95% CI, 0.82-0.92 for postprandial C-peptide, P<0.001; OR, 0.88; 95% CI, 0.82-0.94 for ΔC-peptide, P<0.001) after adjustment for age, gender, and other confounding factors including eGFR.

CONCLUSIONS

Serum C-peptide levels are inversely associated with the prevalence of DR in type 2 diabetic patients independently of eGFR.

Association of blood glucose control and pancreatic reserve with diabetic retinopathy in the Veterans Affairs Diabetes Trial (VADT)

AIMS/HYPOTHESIS

The aim of this study was to test the hypothesis that intensive glycaemic control (INT) and higher plasma C-peptide levels in patients with poorly controlled diabetes would be associated with better eye outcomes.

METHODS

The incidence and progression of diabetic retinopathy (DR) was assessed by grading seven-field stereoscopic fundus photographs at baseline and 5 years later in 858 of 1,791 participants in the Veterans Affairs Diabetes Trial (VADT).

RESULTS

After adjustment for all covariates, risk of progression (but not incidence) of DR increased by 30% for each 1% increase in baseline HbA1c (OR 1.3; 95% CI 1.123, 1.503; p = 0.0004). Neither assignment to INT nor age was independently associated with DR in the entire cohort. However, INT showed a biphasic interaction with age. The incidence of DR was decreased in INT participants ≤55 years of age (OR 0.49; 95% CI 0.24, 1.0) but increased in those ≥70 years old (OR 2.88; 95% CI 1.0, 8.24) (p = 0.0043). The incidence of DR was reduced by 67.2% with each 1 pmol/ml increment in baseline C-peptide (OR 0.328; 95% CI 0.155, 0.7; p = 0.0037). Baseline C-peptide was also an independent inverse risk factor for the progression of DR, with a reduction of 47% with each 1 pmol/ml increase in C-peptide (OR 0.53; 95% CI 0.305, 0.921; p = 0.0244).

CONCLUSIONS/INTERPRETATION

Poor glucose control at baseline was associated with an increased risk of progression of DR. INT was associated with a decreased incidence of DR in younger patients but with an increased risk of DR in older patients. Higher C-peptide at baseline was associated with reduced incidence and progression of DR.

Prevalences of diabetic retinopathy and nephropathy are lower in Korean type 2 diabetic patients with non-alcoholic fatty liver disease

AIMS/INTRODUCTION

The associations between non-alcoholic fatty liver disease (NAFLD) and chronic vascular complications of type 2 diabetes remain uncertain. We assessed the relationships between NAFLD and chronic vascular complications in patients with type 2 diabetes.

MATERIALS AND METHODS

Patients with type 2 diabetes (n = 929) attending a diabetes clinic of a university hospital were studied retrospectively. Patients who had any clinical evidence of cirrhosis or other causes of chronic liver disease were excluded. Prevalences of chronic microvascular and macrovascular complications were assessed. NAFLD was ascertained by ultrasonography.

RESULTS

The prevalence of NAFLD in patients with type 2 diabetes was 63.3%. The prevalences of diabetic retinopathy and nephropathy were significantly lower in patients with NAFLD than those without NAFLD (33.0 vs 70.2%, P < 0.001; 29.3 vs 37.1%, P = 0.007, respectively), whereas no difference was found in the prevalence of diabetic neuropathy. The prevalence of diabetic macrovascular complications was lower in type 2 diabetic patients with NAFLD than those without NAFLD (9.2 vs 14.7%, P = 0.008). After adjustment for confounding factors, such as age, sex, glycated hemoglobin, fasting serum C-peptide, diabetic duration, body mass index and hypertension, NAFLD remained significantly associated with a lower odds ratio (OR) of diabetic retinopathy (OR 0.440, 95% confidence interval 0.255-0.757, P = 0.003) and nephropathy, (OR 0.541, 95% confidence interval 0.358-0.817, P = 0.003). In contrast, NAFLD was not significantly associated with macrovascular complications after adjustment for confounding factors.

CONCLUSIONS

These results suggest that NAFLD is inversely associated with prevalences of diabetic retinopathy and nephropathy in Korean patients with type 2 diabetes.

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.

Correlations between Glucagon Stimulated C-peptide Levels and Microvascular Complications in Type 2 Diabetes Patients

BACKGROUND

This study aimed to investigate whether stimulated C-peptide is associated with microvascular complications in type 2 diabetes mellitus (DM).

METHODS

A cross-sectional study was conducted in 192 type 2 diabetic patients. Plasma basal C-peptide and stimulated C-peptide were measured before and 6 minutes after intravenous injection of 1 mg glucagon. The relationship between C-peptide and microvascular complications was statistically analyzed.

RESULTS

In patients with retinopathy, basal C-peptide was 1.9±1.2 ng/mL, and stimulated C-peptide was 2.7±1.6 ng/mL; values were significantly lower compared with patients without retinopathy (P=0.031 and P=0.002, respectively). In patients with nephropathy, basal C-peptide was 1.6±0.9 ng/mL, and stimulated C-peptide was 2.8±1.6 ng/mL; values were significantly lower than those recorded in patients without nephropathy (P=0.020 and P=0.026, respectively). Stimulated C-peptide level was associated with increased prevalence of microvascular complications. Age-, DM duration-, and hemoglobin A1c-adjusted odds ratios for retinopathy in stimulated C-peptide value were 4.18 (95% confidence interval [CI], 1.40 to 12.51) and 3.35 (95% CI, 1.09 to 10.25), respectively. The multiple regression analysis between nephropathy and C-peptide showed that stimulated C-peptide was statistically correlated with nephropathy (P=0.03).

CONCLUSION

In patients with type 2 diabetes, the glucagon stimulation test was a relatively simple method of short duration for stimulating C-peptide response. Stimulated C-peptide values were associated with microvascular complications to a greater extent than basal C-peptides.

Proinflammatory effects of C-Peptide in different tissues

Atherosclerosis is well known as an inflammatory disease that can lead to clinical complications such as heart attack or stroke. C-peptide as a cleavage product of proinsulin is in the last few decades known as an active peptide with a number of different effects on microvascular and macrovascular complications in type 2 diabetic patients. Patients with insulin resistance and early type 2 diabetes show elevated levels of C-peptide in blood. Several last findings demonstrated deposition of C-peptide in the vessel wall in ApoE-deficient mice and induction of local inflammation. Besides that, C-peptide has proliferative effects on human mesangial cells. This review discusses recently published proinflammatory effects of C-peptide in different tissues.

C-peptide induces human renal mesangial cell proliferation in vitro, activating Src-kinase, PI-3 kinase and ERK1/2

BACKGROUND

Elevated levels of C-peptide have been found in patients with insulin resistance and early type 2 diabetes. These patients are at greater risk to develop micro- and macrovascular complications. Since diabetic nephropathy involves glomerular hyperproliferation, the present study evaluates the role of C-peptide on human renal mesangial cell proliferation.

METHODS AND RESULTS

C-peptide induces proliferation of human renal mesangial cells in a concentration-dependent manner with a maximal 2.6±0.4-fold induction at 10 nmol/L (P<0.05 compared with unstimulated cells; n=6), as revealed by [3H]-thymidine incorporation experiments. The proliferative effect of C-peptide is prevented by Src-kinase inhibitor-PP2, PI-3 kinase inhibitor-LY294002, and the ERK1/2 inhibitor-U126. Moreover, C-peptide induces phosphorylation of Src, as well as activation of PI-3 kinase and ERK1/2. Furthermore, C-peptide induces cyclin D1 expression as well as phosphorylation of retinoblastoma protein (Rb).

CONCLUSIONS

These results demonstrate an active role of C-peptide on the proliferation of human renal mesangial cells in vitro involving PI-3 kinase and MAP kinase signaling pathways, suggesting a possible role of C-peptide in glomerular hyperproliferation in patients with diabetic nephropathy.

Association between serum C-peptide levels and chronic microvascular complications in Korean type 2 diabetic patients

This study evaluated the association between serum C-peptide levels and chronic vascular complications in Korean patients with type 2 diabetes. Data for 1,410 patients with type 2 diabetes were evaluated cross-sectionally. Fasting and postprandial 2-hour serum C-peptide levels were analyzed with respect to diabetic micro- and macrovascular complications. In the group of patients with lower fasting serum C-peptide quartile, the prevalences of diabetic retinopathy and neuropathy were significantly higher (P = 0.035, P < 0.001, respectively). In the group of patients with lower delta C-peptide (postprandial - fasting C-peptide) quartile, the prevalences of diabetic retinopathy, nephropathy, and neuropathy were significantly higher (P < 0.001 for all). Low delta C-peptide quartile was also associated with increased severity of retinopathy and nephropathy. The age- and sex-adjusted odds ratios (ORs) for retinopathy, neuropathy, and nephropathy in the lowest versus the highest delta C-peptide quartile were 6.45 (95% confidence interval 3.41-12.22), 3.01 (2.16-4.19), and 2.65 (1.71-4.12), respectively. After further adjustment for the duration of diabetes, type of antidiabetic therapy, mean hemoglobin A1c, body mass index, and blood pressure, the ORs were reduced to 2.83 (1.32-6.08), 1.68 (1.12-2.53), and 1.61 (1.05-2.47), respectively, but remained significant. No significant difference was observed in the prevalence of macrovascular complications with respect to fasting or delta C-peptide quartiles. These results suggest that low C-peptide level is associated with diabetic microvascular, but not macrovascular complications in patients with type 2 diabetes mellitus.

Factor analysis of diabetic nephropathy in Chinese patients

OBJECTIVE

To investigate factors related to albuminuria in diabetic nephropathy (DN).

METHODS

Clinical data of 873 Chinese patients with type 2 diabetes were gathered retrospectively. Urinary albumin-creatinine-ratio was tested thrice for each patient before calculating its mean value for DN diagnosing and staging. Inter-relationship among variables was studied using factor analysis, and factor scores were compared and used as independent variables in regression models to identify the parameter clusters that predict the development and/or progression of DN.

RESULTS

Factor analysis reduced 21 original variables to eight unique factors, representing obesity, glycemic, C peptide, lipids, time, renal, blood pressure and metabolism status. Logistic regression revealed that presence of hyperuricemia/gout (OR=1.821, 95%CI 1.224-2.707), time factor (OR=1.404, 95%CI 1.194-1.651) and blood pressure factor (OR=1.424, 95%CI 1.216-1.668) were positively associated with DN, while C peptide factor (OR=0.816, 95%CI 0.691-0.963) was negatively associated with DN. Ordinal regression revealed another positively related lipid factor (OR=1.237, 95%CI 1.060-1.445) besides those determined in Logistic regression.

CONCLUSION

Hyperuricemia/gout, time, blood pressure and lipid factors are predictors of DN, while C peptide factor is negatively associated with the development and/or progression of DN.

Factor analysis of diabetic retinopathy in Chinese patients

OBJECTIVE

To investigate factors related to diabetic retinopathy (DR).

METHOD

Clinical data of 603 Chinese diabetic patients were analyzed retrospectively. On the basis of its severity, DR was graded as non-diabetic retinopathy (NDR), non proliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR). Factor analysis was conducted and factor scores were used as independent variables in both Logistic and Ordinal regression models to identify the predictors of the development and/or progression of DR.

RESULT

After factor analysis, 21 original variables were finally reduced to eight unique factors, representing obesity, glycemic, C peptide, lipids, time, renal, blood pressure and metabolic factors. Logistic regression revealed that female (OR = 2.208, 95%CI 1.328-3.671), comorbidity of peripheral atherosclerosis (PA) (OR = 2.690, 95%CI 1.000-7.238), time factor (OR = 1.838, 95%CI 1.421-2.377) and renal factor (OR = 2.444, 95%CI 1.757-3.400) were positively associated with DR, while C peptide factor (OR = 0.469, 95%CI 0.365-0.604) was negatively associated with DR. Besides another negatively related obesity factor (OR = 0.777), Ordinal regression revealed similarly related factors, but ruled out the influence of gender and PA.

CONCLUSION

Female, macrovascular complications, time and renal factors are predictors of DR, while C peptide factor is negatively associated with the development and/or progression of DR.

C-peptide and chronic complications in patients with type-2 diabetes and the metabolic syndrome

INTRODUCTION

We investigated the relation between C-peptide levels and the prevalence of diabetic complications in patients with type 2 diabetes and the metabolic syndrome.

METHODS

This study includes all patients with diabetes and treated only with oral hypoglycemic agents who were admitted to our department in 2006. The chronic complications of diabetes (vascular disease, retinopathy, nephropathy, neuropathy) were evaluated.

RESULTS

The 77 patients with type 2 diabetes and treated only with oral hypoglycemic agents were divided in two groups, with and without the metabolic syndrome. The two groups did not differ in glycemic control, blood pressure levels, or duration of diabetes. CRP levels were higher in patients with the metabolic syndrome (p=0.03), and nephropathy was more common (70%, compared with 33%). Similar, C-peptide levels were higher in patients with the metabolic syndrome: 3.12+/-1.36 compared with 1.82+/-1.25 (p<0.001). In patients with the metabolic syndrome, C-peptide levels did not differ in patients with or without diabetic complications (3.01+/-1.16, compared with 3.96+/-2.55; p=0.51). Similarly, C-peptide levels in patients without the metabolic syndrome did not differ according to the presence of complications of diabetes (2.25+/-1.21 versus 1.36+/-1.16; p=0.07). However, C-peptide levels were higher in patients with diabetes and the metabolic syndrome who had either nephropathy or vascular disease, compared with those with those complications but without the metabolic syndrome (p=0.01). CRP levels did not correlate with C-peptide levels in any patient group.

DISCUSSION

Higher C-peptide levels were associated with metabolic syndrome in patients with type 2 diabetes and in diabetes patients who also had nephropathy and vascular disease.

The effects of calcitriol and nicotinamide on residual pancreatic beta-cell function in patients with recent-onset Type 1 diabetes (IMDIAB XI)

BACKGROUND

A number of recent studies underline the importance of vitamin D in the pathogenesis of Type 1 diabetes (T1D).

AIMS

The aim of this study was to investigate whether supplementation with the active form of vitamin D (calcitriol) in subjects with recent-onset T1D protects residual pancreatic beta-cell function and improves glycaemic control (HbA(1c) and insulin requirement).

METHODS

In this open-label randomized trial, 70 subjects with recent-onset T1D, mean age 13.6 years +/- 7.6 sd were randomized to calcitriol (0.25 microg on alternate days) or nicotinamide (25 mg/kg daily) and followed up for 1 year. Intensive insulin therapy was implemented with three daily injections of regular insulin + NPH insulin at bedtime.

RESULTS

No significant differences were observed between calcitriol and nicotinamide groups in respect of baseline/stimulated C-peptide or HbA1c 1 year after diagnosis, but the insulin dose at 3 and 6 months was significantly reduced in the calcitriol group.

CONCLUSIONS

At the dosage used, calcitriol has a modest effect on residual pancreatic beta-cell function and only temporarily reduces the insulin dose.

Beneficial effects of fish liver preparations of sea bass (Lates calcarifer) versus gemfibrozil in high fat diet-induced lipid-intolerant rats

Abnormal lipid metabolism is a main cause of dyslipidemia, which is a major risk factor for coronary heart disease and obesity and is even linked to diabetic-dyslipidemic complications. Fifteen days of high-fat feeding in Charles Foster rats resulted in a significant increase in baseline serum lipid levels accompanied by pronounced dyslipidemia. Treatment with fish liver preparations (FLPs) from sea bass and the standard drug gemfibrozil produced a lowering of serum lipids and glucose levels, along with a fall in very-low-density and low-density lipoprotein and an increase in high-density lipoprotein levels. Simultaneously, reactivation of plasma postheparin lipolytic activity (PHLA) and lecithin:cholesterol acyltransferase (LCAT) activity was also observed. A positive correlation was observed between low-density lipoprotein activity and fecal bile acid excretion, which was enhanced on treatment with FLPs and gemfibrozil, indicating the catabolic process for normal lipids and cholesterol homeostasis. These data suggest that FLPs and gemfibrozil not only lower lipid intolerance but also reduce diabetic-dyslipidemic complications by activating peroxisome proliferator-activated receptors (PPAR).

Random C-peptide in the classification of diabetes

OBJECTIVE

To clarify whether random C-peptide is a valuable test in the classification of diabetes.

RESEARCH DESIGN AND METHODS

All C-peptide measurements conducted in the diabetic population of Skaraborg (280,539 inhabitants and 3.2% diabetes) between 1995 and 1998 (3,115 samples) were considered, but only patients with well-defined diabetes type (1,449 samples from 1,093 patients) were analyzed for the correlation between diabetes type and C-peptide concentration. Serum C-peptide was measured after fasting over night (fCP), after glucagon stimulation (gCP), and randomly (rCP) without considering previous meals at an ordinary visit to the diabetic clinic (rCP). Receiver Operating Characteristic (ROC) curves were constructed to illustrate the power of the different C-peptide protocols and to determine the optimal cut-off values.

RESULTS

Although all three tests had high discriminative power, the ROC curves demonstrated that rCP was superior to fCP and gCP in discriminating type 1 from type 2 diabetes. The optimal cut-off value for rCP was 0.50 nmol/L, for fCP 0.42 nmol/L, and for gCP 0.60 nmol/L.

CONCLUSIONS

rCP is more powerful than fCP and gCP in distinguishing type 1 from type 2 diabetes and can therefore be recommended as a classification tool, particularly in outpatients.