Point-of-Care HbA1c in Clinical Practice: Caveats and Considerations for Optimal Use.

Hemoglobin A1c (A1C) is widely used for the diagnosis and management of diabetes. Accurate measurement of A1C is necessary for optimal clinical value. Assay standardization has markedly improved the accuracy and consistency of A1C testing. Devices to measure A1C at point of care (POC) are commercially available, allowing rapid results when the patient is seen. In this review, we describe how standardization of A1C testing was achieved, leading to high-quality results in clinical laboratories. We address the use of POC A1C testing in clinical situations and summarize the advantages and disadvantages of POC A1C testing. We emphasize the importance of considering the limitations of these devices and following correct testing procedures to ensure that accurate A1C results are obtained for optimal care of patients.

Interlaboratory Comparison of Antibody-Free LC-MS/MS Measurements of C-peptide and Insulin.

BACKGROUND: The enhanced precision and selectivity of liquid chromatography-tandem mass spectrometry (LC-MS/MS) makes it an attractive alternative to certain clinical immunoassays. Easily transferrable work flows could help facilitate harmonization and ensure high-quality patient care. We aimed to evaluate the interlaboratory comparability of antibody-free multiplexed insulin and C-peptide LC-MS/MS measurements. METHODS: The laboratories that comprise the Targeted Mass Spectrometry Assays for Diabetes and Obesity Research (TaMADOR) consortium verified the performance of a validated peptide-based assay (reproducibility, linearity, and lower limit of the measuring interval [LLMI]). An interlaboratory comparison study was then performed using shared calibrators, de-identified leftover laboratory samples, and reference materials. RESULTS: During verification, the measurements were precise (2.7% to 3.7%CV), linear (4 to 15 ng/mL for C-peptide and 2 to 14 ng/mL for insulin), and sensitive (LLMI of 0.04 to 0.10 ng/mL for C-peptide and 0.03 ng/mL for insulin). Median imprecision across the 3 laboratories was 13.4% (inter-quartile range [IQR] 11.6%) for C-peptide and 22.2% (IQR 20.9%) for insulin using individual measurements, and 10.8% (IQR 8.7%) and 15.3% (IQR 14.9%) for C-peptide and insulin, respectively, when replicate measurements were averaged. Method comparison with the University of Missouri reference method for C-peptide demonstrated a robust linear correlation with a slope of 1.044 and r2 = 0.99. CONCLUSIONS: Our results suggest that combined LC-MS/MS measurements of C-peptide and insulin are robust and adaptable and that standardization with a reference measurement procedure could allow accurate and precise measurements across sites, which could be important to diabetes research and help patient care in the future.

C-peptide determination in the diagnosis of type of diabetes and its management: A clinical perspective.

Impaired beta-cell function is a recognized cornerstone of diabetes pathophysiology. Estimates of insulin secretory capacity are useful to inform clinical practice, helping to classify types of diabetes, complication risk stratification and to guide treatment decisions. Because C-peptide secretion mirrors beta-cell function, it has emerged as a valuable clinical biomarker, mainly in autoimmune diabetes and especially in adult-onset diabetes. Nonetheless, the lack of robust evidence about the clinical utility of C-peptide measurement in type 2 diabetes, where insulin resistance is a major confounder, limits its use in such cases. Furthermore, problems remain in the standardization of the assay for C-peptide, raising concerns about comparability of measurements between different laboratories. To approach the heterogeneity and complexity of diabetes, reliable, simple and inexpensive clinical markers are required that can inform clinicians about probable pathophysiology and disease progression, and so enable personalization of management and therapy. This review summarizes the current evidence base about the potential value of C-peptide in the management of the two most prevalent forms of diabetes (type 2 diabetes and autoimmune diabetes) to address how its measurement may assist daily clinical practice and to highlight current limitations and areas of uncertainties to be covered by future research.

Evaluation of interference from hemoglobin C, D, E and S traits on measurements of hemoglobin A1c by fifteen methods.

BACKGROUND: Hemoglobin C, D Punjab, E or S trait can interfere with hemoglobin A1c (HbA1c) results. We assessed whether they affect results obtained with 15 current assay methods. METHODS: Hemoglobin AA (HbAA), HbAC, HbAD Punjab, HbAE and HbAS samples were analyzed on 2 enzymatic, 4 ion-exchange HPLC and 9 immunoassay methods. Trinity Premier Hb9210 boronate affinity HPLC was the comparative method. An overall test of coincidence of least-squared linear regression lines was performed to determine if HbA1c results were statistically significantly different from those of HbAA samples. Clinically significant interference was defined as >6% difference from HbAA at 6 or 9% HbA1c compared to Premier Hb9210 using Deming regression. RESULTS: All methods showed statistically significant effects for one or more variants. Clinically significant effects were observed for the Tosoh G11 variant mode (HbAD), Roche b 101 (HbAC and HbAE) and Siemens DCA Vantage (HbAE and HbAS). All other methods (Beckman Coulter B93009 and B00389 on DxC700AU, and Unicel DxC, Ortho Clinical Vitros 5.1, Roche cobas c 513, Siemens Dimension RxL and Vista, and Enzymatic on Advia and Atellica, Tosoh G8 5.24 and 5.28, and GX) showed no clinically significant differences. CONCLUSIONS: A few methods showed interference from one or more variants. Laboratories need to be aware of potential HbA1c assay interferences.

Continuous Glucose Monitoring and Use of Alternative Markers To Assess Glycemia in Chronic Kidney Disease.

OBJECTIVE: In chronic kidney disease, glycated albumin and fructosamine have been postulated to be better biomarkers of glycemic control than HbA1c. We evaluated the accuracy, variability, and covariate bias of three biomarkers (HbA1c, glycated albumin, and fructosamine) compared with continuous glucose monitoring (CGM)-derived measurement of glycemia across estimated glomerular filtration rate (eGFR) in type 2 diabetes. RESEARCH DESIGN AND METHODS: A prospective cohort study was conducted of 104 participants with type 2 diabetes, 80 with eGFR <60 mL/min/1.73 m2 (not treated with dialysis) and 24 frequency-matched control subjects with eGFR ≥60 mL/min/1.73 m2. Participants wore a blinded CGM for two 6-day periods separated by 2 weeks, with blood and urine collected at the end of each CGM period. HbA1c, glycated albumin, and fructosamine were measured by high-performance liquid chromatographic, enzymatic, and colorimetric nitroblue tetrazolium methods, respectively. RESULTS: Within-person biomarker values were strongly correlated between the two CGM periods (r = 0.92-0.95), although no marker fully captured the within-person variability of mean CGM glucose. All markers were similarly correlated with mean CGM glucose (r = 0.71-77). Compared with mean CGM glucose, glycated albumin and fructosamine were significantly biased by age, BMI, serum iron concentration, transferrin saturation, and albuminuria; HbA1c was underestimated in those with albuminuria. CONCLUSIONS: Glycated albumin and fructosamine were not less variable than HbA1c at a given mean CGM glucose level, with several additional sources of bias. These results support measuring HbA1c to monitor trends in glycemia among patients with eGFR <60 mL/min/1.73 m2. Direct measurements of glucose are necessary to capture short-term variability.

Accuracy and Precision of a Point-of-Care HbA1c Test.

BACKGROUND: Point-of-care (POC) hemoglobin A1c (HbA1c) testing has advantages over laboratory testing, but some questions have remained regarding the accuracy and precision of these methods. The accuracy and the precision of the POC Afinion™ HbA1c Dx test were investigated. METHODS: Samples spanning the assay range were collected from prospectively enrolled subjects at three clinical sites. The accuracy of the POC test using fingerstick and venous whole blood samples was estimated via correlation and bias with respect to values obtained by an NGSP secondary reference laboratory (SRL). The precision of the POC test using fingerstick samples was estimated from duplicate results by calculating the coefficient of variation (CV) and standard deviation (SD), and separated into its components using analysis of variance (ANOVA). The precision of the POC test using venous blood was evaluated from samples run in four replicates on each of three test cartridge lots, twice per day for 10 consecutive days. The SD and CV by study site and overall were calculated. RESULTS: Across the assay range, POC test results from fingerstick and venous whole blood samples were highly correlated with results from the NGSP SRL (r = .99). The mean bias was -0.021% HbA1c (-0.346% relative) using fingerstick samples and -0.005% HbA1c (-0.093% relative) using venous samples. Imprecision ranged from 0.62% to 1.93% CV for fingerstick samples and 1.11% to 1.69% CV for venous samples. CONCLUSIONS: The results indicate that the POC test evaluated here is accurate and precise using both fingerstick and venous whole blood.

Hypoglycemia in People with Type 2 Diabetes and CKD.

BACKGROUND AND OBJECTIVES: Among people with diabetes mellitus, CKD may promote hypoglycemia through altered clearance of glucose-lowering medications, decreased kidney gluconeogenesis, and blunted counter-regulatory response. We conducted a prospective observational study of hypoglycemia among 105 individuals with type 2 diabetes treated with insulin or a sulfonylurea using continuous glucose monitors. DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS: We enrolled 81 participants with CKD, defined as eGFR<60 ml/min per 1.73 m2, and 24 control participants with eGFR≥60 ml/min per 1.73 m2 frequency-matched on age, duration of diabetes, hemoglobin A1c, and glucose-lowering medications. Each participant wore a continuous glucose monitor for two 6-day periods. We examined rates of sustained level 1 hypoglycemia (<70 mg/dl) and level 2 hypoglycemia (<54 mg/dl) among participants with CKD. We then tested differences compared with control participants as well as a second control population (n=73) using Poisson and linear regression, adjusting for age, sex, and race. RESULTS: Over 890 total days of continuous glucose monitoring, participants with CKD were observed to have 255 episodes of level 1 hypoglycemia, of which 68 episodes reached level 2 hypoglycemia. Median rate of hypoglycemic episodes was 5.3 (interquartile range, 0.0-11.7) per 30 days and mean time spent in hypoglycemia was 28 (SD 37) minutes per day. Hemoglobin A1c and the glucose management indicator were the main clinical correlates of time in hypoglycemia (adjusted differences 6 [95% confidence interval, 2 to 10] and 13 [95% confidence interval, 7 to 20] fewer minutes per day per 1% higher hemoglobin A1c or glucose management indicator, respectively). Compared with control populations, participants with CKD were not observed to have significant differences in time in hypoglycemia (adjusted differences 4 [95% confidence interval, -12 to 20] and -12 [95% confidence interval, -29 to 5] minutes per day). CONCLUSIONS: Among people with type 2 diabetes and moderate to severe CKD, hypoglycemia was common, particularly with tighter glycemic control, but not significantly different from groups with similar clinical characteristics and preserved eGFR.

The National Glycohemoglobin Standardization Program: Over 20 Years of Improving Hemoglobin A1c Measurement.

BACKGROUND: Measurement of hemoglobin A1c (HbA1c) in the blood is integral to and essential for the treatment of patients with diabetes mellitus. HbA1c reflects the mean blood glucose concentration over the preceding 8 to 12 weeks. Although the clinical value of HbA1c was initially limited by large differences in results among various methods, the investment of considerable effort to implement standardization has brought about a marked improvement in analysis. CONTENT: The focus of this review is on the substantial progress that has been achieved in enhancing the accuracy and, therefore, the clinical value of HbA1c assays. SUMMARY: The interactions between the National Glycohemoglobin Standardization Program and manufacturers of HbA1c methods have been instrumental in standardizing HbA1c. Proficiency testing using whole blood has allowed accuracy-based assessment of methods in individual clinical laboratories that has made an important contribution to improving the HbA1c measurement in patient samples. These initiatives, supported by the efforts of the IFCC network, have led to a continuing enhancement of HbA1c methods.Many of the factors that previously influenced HbA1c results independently of blood glucose have been eliminated from most modern methods. These include carbamylation, labile intermediates, and common hemoglobin variants. Nevertheless, some factors (e.g., race and aging) may alter HbA1c interpretation, but whether these differences have clinical implications remains contentious. HbA1c has a fundamental role in the diagnosis and management of diabetes. Ongoing improvements in HbA1c measurement and quality will further enhance the clinical value of this analyte.

Multicenter assessment of a hemoglobin A1c point-of-care device for diagnosis of diabetes mellitus.

OBJECTIVE: A multisite investigation compared the analytical performance of a point-of-care (POC) HbA1c device with multiple commonly used HbA1c laboratory methods and an NGSP (National Glycohemoglobin Standardization Program) reference method. RESEARCH DESIGN AND METHODS: The Afinion AS100 POC device analyzed HbA1c using 618 EDTA whole blood excess patient specimens with clinically indicated HbA1c testing. Results were compared to measurements across five clinical laboratories and the NGSP reference method. Precision was evaluated over 8-10 consecutive days for low-, mid-, and high-range HbA1c specimens at all five sites. RESULTS: Over a wide range of HbA1c values (4.0%-15% HbA1c), 97.1% of the POC results and 94.5% of routine laboratory results fell within the target value of ±6% of the NGSP reference method results. The POC HbA1c results at 6.5% exhibited a total relative bias of -0.6% (-0.04% HbA1c) compared to the reference method while the aggregate of laboratory methods displayed a relative bias of -0.9% (-0.06% HbA1c). The total imprecision of the POC results ranged from 0.74-2.13% CV across the analytic measurement range compared to 0.81-3.23% CV for the routine laboratory methods. CONCLUSIONS: The accuracy and precision of the Afinion POC HbA1c method was comparable to the laboratory HbA1c methods supporting the FDA's recent approval of the Afinion HbA1c Dx device for use in the diagnosis of diabetes.

Recognition of rare hemoglobin variants by hemoglobin A1c measurement procedures.

BACKGROUND: Unrecognized hemoglobinopathies can lead to measured hemoglobin A1c (Hb A1c) concentrations that are erroneous or misleading. We determined the effects of rare hemoglobin variants on capillary electrophoresis (CE) and HPLC methods for measurement of Hb A1c. METHODS: We prospectively investigated samples in which Hb A1c was measured by CE during a 14-month period. For samples in which the electropherograms suggested the presence of rare hemoglobinopathies, hemoglobin variants were identified by molecular analysis or by comparison with electropherograms of known variants. When sample volume permitted, Hb A1c was measured by 2 HPLC measurement procedures and by boronate affinity HPLC. RESULTS: Hb A1c was measured by CE in 33,859 samples from 26,850 patients. 15 patients (0.06%) were identified as having rare hemoglobinopathies: Hbs A2 prime, Agenogi, Fannin-Lubbock I, G Philadelphia, G San Jose, J Baltimore, La Desirade, N Baltimore, Nouakchott, and Roanne. Among 6 of these samples tested by 2 ion-exchange HPLC methods, the rare Hb was detected by both HPLC methods in only one sample, and none were detected by boronate affinity HPLC. The mean of the Hb A1c results of 2 HPLC methods differed from the result of the CE method by 0.7-2.2% Hb A1c in samples with variant hemoglobins versus <0.2% Hb A1c in samples without variants. CONCLUSION: Measurement procedures differ in the ability to detect the presence of rare Hb variants and to quantify Hb A1c in patients who harbor such variants.

Implementing a Reference Measurement System for C-Peptide: Successes and Lessons Learned.

BACKGROUND: Assessment of endogenous insulin secretion by measuring C-peptide concentrations is widely accepted. Recent studies have shown that preservation of even small amounts of endogenous C-peptide production in patients with type 1 diabetes reduces risks for diabetic complications. Harmonization of C-peptide results will facilitate comparison of data from different research studies and later among clinical laboratory results at different sites using different assay methods. CONTENT: This review provides an overview of the general process of harmonization and standardization and the challenges encountered with implementing a reference measurement system for C-peptide. SUMMARY: Efforts to harmonize C-peptide results are described, including those by the National Institute of Diabetes and Digestive and Kidney Diseases-led C-peptide Standardization Committee in the US, activities in Japan, efforts by the National Institute for Biological Standards and Control in the UK, as well as activities led by the Bureau International des Poids et Mesures and the National Metrology Institute in China. A traceability scheme is proposed along with the next steps for implementation. Suggestions are made for better collaboration to optimize the harmonization process for other measurands.