[Show abstract][Hide abstract] ABSTRACT: C-peptide measurement has been widely used as a marker of insulin secretion in patients with diabetes. We assessed the comparability of C-peptide results obtained with different methods and by different laboratories and determined whether C-peptide results could be harmonized by normalization with a WHO reference reagent or with plasma.
We sent 16 different heparin plasma samples to 15 laboratories in 7 countries. The samples were analyzed with 10 different assay methods. A WHO C-peptide standard was also sent to each laboratory and used to determine the feasibility of normalizing results. To assess the impact of calibrator matrix on the comparability of results, we also used the mean results of all laboratories for 4 of the samples to normalize the remaining sample results.
Between-laboratory variability increased with increasing C-peptide concentrations. Normalization of results with WHO reference reagents did not improve comparability, but normalization with samples significantly improved comparability among laboratories and methods. The 95% confidence interval estimate for the SD for the lab/method effect (0.0-0.061) using sample-normalized values did not overlap with the 95% CI estimate with the raw data (0.090-0.225).
C-peptide results generated by different methods and different laboratories do not always agree, especially at higher concentrations of C-peptide. These data support the concept of using a single laboratory for multisite studies and support efforts to harmonize C-peptide measurements by use of calibrators prepared in the sample matrix.
[Show abstract][Hide abstract] ABSTRACT: Clinical trials require assays that provide consistent results during the course of a study. The hemoglobin A1c (HbA1c) assay, a measure of chronic glycemia, is critical to the study of diabetes control and complications.
The Diabetes Control and Complications Trial (DCCT) and its follow-up study, the Epidemiology of Diabetes Interventions and Complications (EDIC), required 20 years of consistent HbA1c results, measured by three different ion-exchange HPLC procedures. To maintain and document consistent HbA1c results measured in the DCCT and EDIC Central Biochemistry Laboratory, a backup laboratory used frozen hemolysates as long-term calibrators and a HPLC method with a single lot of Bio-Rex 70 resin.
Over 20 years, long-term quality-control values have remained constant. Four studies of nondiabetic ranges produced nearly identical values [mean (SD), 5.1 (0.5)%, 4.9 (0.3)%, 5.0 (0.4)%, and 5.0 (0.3)%].
The overall consistency of the HbA1c assays during the 20-year course of the DCCT and EDIC has been critical in establishing the benefits of intensive therapy and in understanding the relationship between long-term glycemia and the development and progression of the complications of diabetes.
[Show abstract][Hide abstract] ABSTRACT: Multiple laboratory tests are used in the diagnosis and management of patients with diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.
An expert committee drafted evidence-based recommendations for the use of laboratory analysis in patients with diabetes. An external panel of experts reviewed a draft of the guidelines, which were modified in response to the reviewers' suggestions. A revised draft was posted on the Internet and was presented at the AACC Annual Meeting in July, 2000. The recommendations were modified again in response to oral and written comments. The guidelines were reviewed by the Professional Practice Committee of the American Diabetes Association.
Measurement of plasma glucose remains the sole diagnostic criterion for diabetes. Monitoring of glycemic control is performed by the patients, who measure their own plasma or blood glucose with meters, and by laboratory analysis of glycated hemoglobin. The potential roles of noninvasive glucose monitoring, genetic testing, autoantibodies, microalbumin, proinsulin, C-peptide, and other analytes are addressed.
The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are of minimal clinical value at the present time, and measurement of them is not recommended.
[Show abstract][Hide abstract] ABSTRACT: To define the relationship between HbA(1c) and plasma glucose (PG) levels in patients with type 1 diabetes using data from the Diabetes Control and Complications Trial (DCCT).
The DCCT was a multicenter, randomized clinical trial designed to compare intensive and conventional therapies and their relative effects on the development and progression of diabetic complications in patients with type 1 diabetes. Quarterly HbA(1c) and corresponding seven-point capillary blood glucose profiles (premeal, postmeal, and bedtime) obtained in the DCCT were analyzed to define the relationship between HbA(1c) and PG. Only data from complete profiles with corresponding HbA(1c) were used (n = 26,056). Of the 1,441 subjects who participated in the study, 2 were excluded due to missing data. Mean plasma glucose (MPG) was estimated by multiplying capillary blood glucose by 1.11. Linear regression analysis weighted by the number of observations per subject was used to correlate MPG and HbA(1c).
Linear regression analysis, using MPG and HbA(1c) summarized by patient (n = 1,439), produced a relationship of MPG (mmol/l) = (1.98 . HbA(1c)) - 4.29 or MPG (mg/dl) = (35.6 . HbA(1c)) - 77.3, r = 0.82). Among individual time points, afternoon and evening PG (postlunch, predinner, postdinner, and bedtime) showed higher correlations with HbA(1c) than the morning time points (prebreakfast, postbreakfast, and prelunch).
We have defined the relationship between HbA(1c) and PG as assessed in the DCCT. Knowing this relationship can help patients with diabetes and their healthcare providers set day-to-day targets for PG to achieve specific HbA(1c) goals.
Diabetes Care 03/2002; 25(2):275-8. DOI:10.2337/diacare.25.2.275 · 8.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: The Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS) demonstrated conclusively that risks for complications in patients with diabetes are directly related to glycemic control, as measured by glycohemoglobin (GHB). In 1994, one year after the DCCT results were reported, the American Diabetes Association (ADA) set specific diabetes treatment goals. However, 1993 College of American Pathologists (CAP) Survey results indicated a lack of comparability of GHB test results among methods and laboratories that represented a major obstacle to meaningful implementation of the ADA guidelines. Thus, an AACC subcommittee was formed in 1993 to develop a standardization program that would enable laboratories to report DCCT-traceable GHB results. This program was implemented in 1996 by the National Glycohemoglobin Standardization Program (NGSP) Steering Committee. APPROACH: We review the NGSP process and summarize progress in standardization through analysis of CAP data. CONTENT: Since 1996, the number of methods and laboratories certified by the NGSP as traceable to the DCCT has steadily increased. CAP GH2-B survey results reported in December 2000 show marked improvement over 1993 data in the comparability of GHB results. In 2000, 90% of surveyed laboratories reported GHB results as hemoglobin A(1c) (HbA(1c)) or equivalent, compared with 50% in 1993. Of laboratories reporting HbA(1c) in 2000, 78% used a NGSP-certified method. For most certified methods in 2000, between-laboratory CVs were <5%. For all certified methods in 2000, the mean percent HbA(1c) was within 0.8% HbA(1c) of the NGSP target at all HbA(1c) concentrations.
[Show abstract][Hide abstract] ABSTRACT: To evaluate the use of GHb as a screening test for undiagnosed diabetes (fasting plasma glucose > or =7.0 mmol/l) in a representative sample of the U.S. population.
The Third National Health and Nutrition Examination Survey included national samples of non-Hispanic whites, non-Hispanic blacks, and Mexican Americans aged > or =20 years. Of these subjects, 7,832 participated in a morning examination session, of which 1,273 were excluded because of a previous diagnosis of diabetes, missing data, or fasting time of <8 h before examination. Venous blood was obtained to measure fasting plasma glucose and GHb in the remaining 6,559 subjects. Receiver operating characteristic curve analysis was used to examine the sensitivity and specificity of GHb for detecting diabetes at increasing GHb cutoff levels.
GHb demonstrated high sensitivity (83.4%) and specificity (84.4%) for detecting undiagnosed diabetes at a GHb cutoff of 1 SD above the normal mean. Moderate sensitivity (63.2%) and very high specificity (97.4%) were evident at a GHb cutoff of 2 SD above the normal mean. Sensitivity at this level ranged from 58.6% in the non-Hispanic white population to 83.6% in the Mexican-American population; specificity ranged from 93.0% in the nonHispanic black population to 98.3% in the non-Hispanic white population.
GHb is a highly specific and convenient alternative to fasting plasma glucose for diabetes screening. A GHb value of 2 SD above the normal mean could identify a high proportion of individuals with undiagnosed diabetes who are at risk for developing diabetes complications.
Diabetes Care 02/2000; 23(2):187-91. DOI:10.2337/diacare.23.2.187 · 8.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study used individual growth modeling to examine individual difference and group difference models of adaptation. The adaptation of 27 children with juvenile rheumatoid arthritis (JRA) and 40 children with insulin-dependent diabetes mellitus (IDDM) was tracked for 18 months from diagnosis. A control group of 62 healthy children was followed over the same time period. Clustering procedures indicated that child and family adaptation could be described by a number of distinct adaptation trajectories, independent of diagnostic group membership. In contrast, parental adaptation trajectory was associated with diagnostic group membership and control over disease activity for the JRA group and with diagnostic group membership for healthy controls. The observation of common patterns across trajectory sets, as well as the finding that trajectories were differentially related to a number of variables of interest, support the use of trajectories to represent adaptation to chronic disease.
Journal of Consulting and Clinical Psychology 07/1998; 66(3):521-32. DOI:10.1037/0022-006X.66.3.521 · 4.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective:
Research in the areas of pediatric rheumatology and pediatric chronic illness has emphasized comprehensive models of adaptation involving risk and resistance factors. This study examined adaptation, within this framework, among a large sample of children with chronic illness and children without chronic illness.
A comprehensive battery of adaptation measures was administered to a sample of 107 children with juvenile rheumatoid arthritis, 114 children with insulin-dependent diabetes mellitus, and 88 healthy controls.
Medical diagnosis was associated with mothers' depression and a composite measure of parental (mother and father) distress and passive coping. Children's emotional and behavioral functioning was not related to medical diagnosis, but mothers' depression and parental distress were associated with child behavior problems.
Because parental distress was associated with child functioning, interventions to ameliorate parental distress may have beneficial effects on the children's behavior and on parents' reactions to their children.
[Show abstract][Hide abstract] ABSTRACT: This study used individual growth modeling to examine individual difference and group difference models of adaptation. The adaptation of 27 children with juvenile rheumatoid arthritis (JRA) and 40 children with insulin-dependent diabetes meilitus (IDDM) was tracked for 18 months from diagnosis. A control group of 62 healthy children was followed over the same time period. Clustering procedures indicated that child and family adaptation could be described by a number of distinct adaptation trajectories, independent of diagnostic soup membership. In contrast, parental adaptation trajectory was associated with diagnostic group membership and control over disease activity for the JRA group and with diagnostic group membership for healthy controls. The observation of common patterns across trajectory sets, as well as the finding that trajectories were differentially related to a number of variables of interest, support the use of trajectories to represent adaptation to chronic disease.
Journal of Consulting and Clinical Psychology 06/1998; 66(3):521-532. DOI:10.1037//0022-006X.66.3.521 · 4.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To evaluate the prevalence and time trends for diagnosed and undiagnosed diabetes, impaired fasting glucose, and impaired glucose tolerance in U.S. adults by age, sex, and race or ethnic group, based on data from the Third National Health and Nutrition Examination Survey, 1988-1994 (NHANES III) and prior Health and Nutrition Examination Surveys (HANESs).
NHANES III contained a probability sample of 18,825 U.S. adults > or = 20 years of age who were interviewed to ascertain a medical history of diagnosed diabetes, a subsample of 6,587 adults for whom fasting plasma glucose values were obtained, and a subsample of 2,844 adults between 40 and 74 years of age who received an oral glucose tolerance test. The Second National Health and Nutrition Examination Survey, 1976-1980, and Hispanic HANES used similar procedures to ascertain diabetes. Prevalence was calculated using the 1997 American Diabetes Association fasting plasma glucose criteria and the 1980-1985 World Health Organization (WHO) oral glucose tolerance test criteria.
Prevalence of diagnosed diabetes in 1988-1994 was estimated to be 5.1% for U.S. adults > or = 20 years of age (10.2 million people when extrapolated to the 1997 U.S. population). Using American Diabetes Association criteria, the prevalence of undiagnosed diabetes (fasting plasma glucose > or = 126 mg/dl) was 2.7% (5.4 million), and the prevalence of impaired fasting glucose (110 to < 126 mg/dl) was 6.9% (13.4 million). There were similar rates of diabetes for men and women, but the rates for non-Hispanic blacks and Mexican-Americans were 1.6 and 1.9 times the rate for non-Hispanic whites. Based on American Diabetes Association criteria, prevalence of diabetes (diagnosed plus undiagnosed) in the total population of people who were 40-74 years of age increased from 8.9% in the period 1976-1980 to 12.3% by 1988-1994. A similar increase was found when WHO criteria were applied (11.4 and 14.3%).
The high rates of abnormal fasting and postchallenge glucose found in NHANES III, together with the increasing frequency of obesity and sedentary lifestyles in the population, make it likely that diabetes will continue to be a major health problem in the U.S.
Diabetes Care 04/1998; 21(4):518-24. DOI:10.2337/diacare.21.4.518 · 8.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The monitoring of glycemic status is considered a cornerstone of diabetes care. This article reviews current recommendations for routine glycemia monitoring, with emphasis on practical applications. A description of the newly developed National Glycohemoglobin Standardization Program also is provided.
Endocrinology & Metabolism Clinics of North America 10/1997; 26(3):475-86. DOI:10.1016/S0889-8529(05)70261-9 · 3.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study examined the relationships of the dispositional variables of hope, positive affectivity (PA), and negative affectivity (NA) with disease status and illness-related psychosocial functioning in a sample of 45 young adults with insulin-dependent diabetes mellitus (IDDM). Canonical analyses revealed one significant canonical function between the dispositional and psychosocial outcome variables. Primary contributors to the relationship were higher NA and lower PA and maladaptive emotional behavior. A linear multiple regression analysis using hope and affectivity as predictors failed to account for a significant proportion of variance in objective disease status as measured by hemoglobin A1C (HbA1C). The results support previous findings that affectivity may relate to self-reported, disease-related outcome, but not necessarily to objective measures of health status. Future studies of adaptation to chronic illness should consider including measures of illness-related behaviors (e.g., adherence), as well as subjective and objective measures of health status.
Journal of Clinical Psychology in Medical Settings 01/1997; 04(1). DOI:10.1023/A:1026284104493 · 1.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To compare glycated hemoglobin (GHb) values of the relationship between glycemic control and complications of diabetes from laboratories involved in long-term studies (Steno, Oslo, Stockholm, Diabetes Control and Complications Trial, and Linköping.)
Blood samples were collected from 25 subjects selected to represent the clinically relevant measurement range. Fresh whole-blood samples were distributed and analyzed within 4 days of sample collection. Pretreatment of samples and analyses of GHb were performed according to the routine method of each study's central or reference laboratory. Results from each laboratory were compared with the group mean, i.e., the mean of all results for each sample.
Regression analyses with the group mean values as independent variables and results from each laboratory as dependent variables showed that Oslo's result had a slope significantly different from the group mean. Laboratories used by the DCCT, Oslo, and Steno studies gave, on average, 0.4, 0.4, and 0.7% higher HbA1c readings than the group mean, respectively, while HbA1c results from Linköping and Stockholm were, on average, 0.6 and 1.0% lower, respectively.
There were large differences in GHb values among laboratories participating in studies of diabetic complications. The present data offer a guide to the comparison of results from the studies and underscores the need for standardization of GHb measurements.
Diabetes Care 08/1996; 19(7):726-9. DOI:10.2337/diacare.19.7.726 · 8.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent large-scale epidemiological studies demonstrate that blood concentrations of immunoreactive insulin predict the development of NIDDM and IDDM and are associated with the risk of several degenerative diseases, such as coronary and peripheral vessel atherosclerosis, hypertension, and dyslipidemia. The reliability of these measurements is dependent on a biological assay that has not been well standardized between laboratories. Recognizing this, the American Diabetes Association organized a task force to assess comparability of blood insulin measurements between laboratories and to suggest techniques to improve comparability. The task force found that identical serum and plasma samples measured in different laboratories produced widely disparate values that were unacceptable for population comparisons. Use of a single reference standard did little to improve comparability. Assay characteristics such as linearity, recovery, accuracy, and cross-reactivity to proinsulin and its primary conversion intermediates varied among the laboratories, and they did not readily explain differences in the measurements made from assay to assay. Use of the same assay kit in different laboratories did not always ensure comparable measurements. Linear regression of assay results from one laboratory to an arbitrarily chosen reference assay greatly improved comparability and demonstrated the potential value in comparing each assay to a reference method. The task force report defines acceptable assay characteristics and proposes a three-step process of insulin assay proficiency and comparability. A central reference assay and ongoing sample exchange will be needed to allow reliable comparisons of insulin measurements made in different laboratories. Rigorous quality control and continuous quality improvement are needed to maintain reliability of the insulin measurement.