![]() However, labs need to look carefully at the antibodies any particular assay targets and the patient population served to ensure the method will yield reliable results, or be prepared to investigate when test results don’t match the patient’s clinical picture.īoronate affinity chromatography also relies on structural variations to detect and quantify Hb with attached glucose residues. On the plus side, immunoassays are affordable, easy to operate, and also easy to add to existing platforms in the laboratory. Patients with Hb F levels above 10% will have a falsely low A1c because the gamma chain of Hb F shares only four of the 10 first amino acids with the ß chain of Hb A, and therefore has little to no immunoreactivity with most antibodies. Interferences from Hb variants depend on where the antibody is targeted and whether a patient’s mutation is in the first few amino acids of the ß chain. Immunoassays are commercially available and, according to the 2014 CAP survey, have variable CVs between 1.6–6.1%. Immunoassays exploit structural variations and use antibodies that target N-terminal glycated amino acids on the ß chain to quantify A1c. Even though ion-exchange HPLC allows for Hb variant detection and has good precision, implementing this platform into the clinical laboratory can be demanding in terms of necessary operator skills and the financial burden of equipment purchase. More common Hb variants can usually be detected by examining the chromatogram, but if the variant can’t be separated from Hb A or A1c, incorrect levels will be reported. According to a 2014 CAP survey, the coefficient of variation (CV) for this method was 1.6–2.7%. Several fully automated systems are available for the clinical laboratory and analysis time is typically less than 5 minutes. Hb Variant Detection Varies Across MethodsĬation-exchange HPLC separates glycated from non-glycated Hb components based on differences in their charges, as glycation of the N-terminal residue decreases its positive charge. And if necessary, alternative methods, such as fructosamine, should be selected to monitor these patients with diabetes. ![]() Efforts should be made to identify Hb variants whenever possible. With any method, if A1c concentrations do not match the clinical picture, then biologic factors-such as altered erythrocyte lifespan-should be considered.Īdditionally, laboratories should be aware of the limitations their method has with respect to Hb variants and communicate this with their clinical colleagues. ![]() are-and evaluate College of American Pathologists (CAP) data to assess how well the method actually performs. When selecting an A1c method labs should first determine if the method is National Glycohemoglobin Standardization Program (NGSP)-certified-better than 99% in the U.S. are performed with these methods, though point-of-care (POC) devices also are used widely.Ī clinical laboratory’s choice of A1c methods depends on factors such as cost, patient population, existing instrumentation, performance, and available resources. ![]() A1c methods fall into two broad categories: those that use molecular charge (ion-exchange high performance liquid chromatography, and electrophoresis) and those that use molecular structure (immunoassay and affinity chromatography). Measuring A1c is an integral component of the standard of care for diabetic patients, and there are a variety of methods to do so. The landmark Diabetes Control and Complications Trial showed that A1c is directly related to risks for diabetic complications, and as a result, clinical guidelines recommend specific treatment goals related to A1c levels. A1c levels reflect not only average blood glucose concentrations during the previous 8 to 12 weeks but also long-term glycemic control. A1c is a specific glycated hemoglobin (Hb) that is modified at the N-terminal valine residue of each ß-chain of Hb A. Hemoglobin A1c (A1c) is an essential component to both the diagnosis and management of patients with diabetes mellitus. ![]()
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