Several studies have shown that vitamin C affects on hemoglobin glycation of proteins. However, the effects on hemoglobin glycation may be interpreted differently depending on the method used to measure glycohemoglobi...Several studies have shown that vitamin C affects on hemoglobin glycation of proteins. However, the effects on hemoglobin glycation may be interpreted differently depending on the method used to measure glycohemoglobin. Six non-diabetic subjects received daily Vitamin C supplementation (500mg Bid) for three months. Fasting blood glucose, plasma vitamin C, HbA1c by ion-exchange HPLC, HbA1c by immunoassay, and total GHB by Affinity HPLC were measured at baseline, and monthly there after for 5 months. Results showed that fasting blood glucose did not change significantly throughout the study. Plasma vitamin C levels increased by 40% (P < 0. 01) by month 1, remained constant during the period of vitamin C intake, then returned to baseline level 2 months after stopping vitamin C supplementation. GHB measured by Affinity HPLC and HbA1c by immunoassay decreased significantly by month 2, remained lower at month 3 and returned to baseline within 2 month of discontinuing vitamin C. HbA1c measured by ion-exchange HPLC, however,was significantly increased within one month of taking vitamin C and remained increased during the period of vitamin C intake. Within 1 month after cessation of vitamin C,ion-exchange HbA1c values. dropped back to baseline levels.We conclude that vitamin C intake causes inhibition of hemoglobin glycation but that the methodology used for GHB measurement may effect interpretation of results. Vitamin C intake interferes directly with measurement of HbA1c by an ion-exchange method falsely increasing results relative to the true amount of GHB, which decreases. However,it should be kept in mind that because of the inhibition of glycation,the actual relationship between GHB and aver age glucose may be altered slightly by Vitamin C intake regardless of the method used.展开更多
The formation of glycohemoglobin, especially the hemoglobin A1c(Hb_(A1c)) fraction, occurs when glucose becomes coupled with the amino acid valine in the β-chain of Hb; this reaction is dependent on the plasma concen...The formation of glycohemoglobin, especially the hemoglobin A1c(Hb_(A1c)) fraction, occurs when glucose becomes coupled with the amino acid valine in the β-chain of Hb; this reaction is dependent on the plasma concentration of glucose. Since the early 1970 s it has been known that diabetics display higher values of Hb_(A1c) because they have elevated blood glucose concentrations. Thus Hb_(A1c) has acquired a very important role in the treatment and diagnosis of diabetes mellitus. After the introduction of the first quantitative measurement of Hb_(A1c), numerous methods for glycohemoglobin have been introduced with different assay principles: From a simple minicolumn technique to the very accurate automated highpressure chromatography and lastly to many automated immunochemical or enzymatic assays. In early days, the results of the quality control reports for Hb_(A1c) varied extensively between laboratories, therefore in United States and Canada working groups(WG) of the Diabetes Controls and Complications Trial(DCCT) were set up to standardize the Hb_(A1c) assays against the DCCT/National Glycohemoglobin Standardization Program reference method based on liquid chromatography. In the 1990 s, the International Federation of Clinical Chemistry and Laboratory Medicine(IFCC) appointed a new WG to plan a reference preparation and method for the Hb_(A1c) measurement. When the reference procedureswere established, in 2004 IFCC recommended that all manufacturers for equipment used in Hb_(A1c) assays should calibrate their methods to their proposals. This led to an improvement in the coefficient of variation(CV%) associated with the assay. In this review, we describe the glycation of Hb, methods, standardization of the Hb_(A1c) assays, analytical problems, problems with the units in which Hb_(A1c) values are expressed, reference values, quality control aspects, target requirements for Hb_(A1c), and the relationship of the plasma glucose values to Hb_(A1c) concentrations. We also note that the acceptance of the mmol/mol system for Hb_(A1c) as recommended by IFCC, i.e., the new unit and reference ranges, are becoming only slowly accepted outside of Europe where it seems that expressing Hb_(A1c) values either only in per cent units or with parallel reporting of percent and mmol/mol will continue. We believe that these issues should be resolved in the future and that it would avoid confusion if mmol/mol unit for Hb_(A1c) were to gain worldwide acceptance.展开更多
文摘Several studies have shown that vitamin C affects on hemoglobin glycation of proteins. However, the effects on hemoglobin glycation may be interpreted differently depending on the method used to measure glycohemoglobin. Six non-diabetic subjects received daily Vitamin C supplementation (500mg Bid) for three months. Fasting blood glucose, plasma vitamin C, HbA1c by ion-exchange HPLC, HbA1c by immunoassay, and total GHB by Affinity HPLC were measured at baseline, and monthly there after for 5 months. Results showed that fasting blood glucose did not change significantly throughout the study. Plasma vitamin C levels increased by 40% (P < 0. 01) by month 1, remained constant during the period of vitamin C intake, then returned to baseline level 2 months after stopping vitamin C supplementation. GHB measured by Affinity HPLC and HbA1c by immunoassay decreased significantly by month 2, remained lower at month 3 and returned to baseline within 2 month of discontinuing vitamin C. HbA1c measured by ion-exchange HPLC, however,was significantly increased within one month of taking vitamin C and remained increased during the period of vitamin C intake. Within 1 month after cessation of vitamin C,ion-exchange HbA1c values. dropped back to baseline levels.We conclude that vitamin C intake causes inhibition of hemoglobin glycation but that the methodology used for GHB measurement may effect interpretation of results. Vitamin C intake interferes directly with measurement of HbA1c by an ion-exchange method falsely increasing results relative to the true amount of GHB, which decreases. However,it should be kept in mind that because of the inhibition of glycation,the actual relationship between GHB and aver age glucose may be altered slightly by Vitamin C intake regardless of the method used.
文摘The formation of glycohemoglobin, especially the hemoglobin A1c(Hb_(A1c)) fraction, occurs when glucose becomes coupled with the amino acid valine in the β-chain of Hb; this reaction is dependent on the plasma concentration of glucose. Since the early 1970 s it has been known that diabetics display higher values of Hb_(A1c) because they have elevated blood glucose concentrations. Thus Hb_(A1c) has acquired a very important role in the treatment and diagnosis of diabetes mellitus. After the introduction of the first quantitative measurement of Hb_(A1c), numerous methods for glycohemoglobin have been introduced with different assay principles: From a simple minicolumn technique to the very accurate automated highpressure chromatography and lastly to many automated immunochemical or enzymatic assays. In early days, the results of the quality control reports for Hb_(A1c) varied extensively between laboratories, therefore in United States and Canada working groups(WG) of the Diabetes Controls and Complications Trial(DCCT) were set up to standardize the Hb_(A1c) assays against the DCCT/National Glycohemoglobin Standardization Program reference method based on liquid chromatography. In the 1990 s, the International Federation of Clinical Chemistry and Laboratory Medicine(IFCC) appointed a new WG to plan a reference preparation and method for the Hb_(A1c) measurement. When the reference procedureswere established, in 2004 IFCC recommended that all manufacturers for equipment used in Hb_(A1c) assays should calibrate their methods to their proposals. This led to an improvement in the coefficient of variation(CV%) associated with the assay. In this review, we describe the glycation of Hb, methods, standardization of the Hb_(A1c) assays, analytical problems, problems with the units in which Hb_(A1c) values are expressed, reference values, quality control aspects, target requirements for Hb_(A1c), and the relationship of the plasma glucose values to Hb_(A1c) concentrations. We also note that the acceptance of the mmol/mol system for Hb_(A1c) as recommended by IFCC, i.e., the new unit and reference ranges, are becoming only slowly accepted outside of Europe where it seems that expressing Hb_(A1c) values either only in per cent units or with parallel reporting of percent and mmol/mol will continue. We believe that these issues should be resolved in the future and that it would avoid confusion if mmol/mol unit for Hb_(A1c) were to gain worldwide acceptance.