Glycosylated haemoglobin levels in patients referred for oral glucose tolerance tests

Stability over time of glycohemoglobin, glucose, and red blood cell survival in hematologically stable people without diabetes

We previously have shown that an affinity, high-performance liquid chromatography (HPLC) method is a highly reproducible and sensitive method for determining percent total glycohemoglobin (tGHb) in people with diabetes. In this study we extended the use of this method to a determination of the correlation of percent tGHb with the fasting plasma glucose concentration in people without known diabetes. We also determined the correlation of the tGHb with the reticulocyte count, as an index of red blood cell (RBC) survival, and with a carbon monoxide (CO) method for determining RBC survival. In addition, the stability of the tGHb, glucose, RBC mass, hemoglobin, and reticulocyte counts over a 1-year period was evaluated. Total glycohemoglobin, overnight fasting plasma glucose concentration, hemoglobin, RBC and reticulocyte count, and the calculated percentage of RBC count represented by reticulocytes were determined monthly for at least 12 months (range, 12 to 26 months) in 48 adults (mean age, 51 years; range, 31 to 82 years). In 37 of the subjects, RBC survival using a CO method also was determined. There was a highly significant linear correlation between the fasting glucose concentration and the tGHb. There was only a weak correlation between the percent reticulocytes or with the RBC survival determined by the CO method. The tGHb, plasma glucose, RBC count, hemoglobin, and percent reticulocytes were very stable over a 12-month or greater period. We conclude that there is a good correlation between the tGHb and plasma glucose concentration in a population without known diabetes. Variations in RBC survival as indicated by a reticulocyte count within the reference range is not likely to have a clinically significant effect on interpretation of tGHb data in the context of an integrated glucose concentration. Nevertheless, this remains to be proven using RBC survival methods that are more precise than those currently available.

A study of the effect of diet on glycosylated haemoglobin and albumin levels and glucose tolerance in normal subjects

As factors other than the degree of glucose tolerance or ambient blood glucose may determine glycosylated haemoglobin levels, we have investigated the effects of dietary glucose and soluble fibre supplementation on glucose tolerance, glycosylated haemoglobin and glycosylated albumin in non-diabetic subjects. Eleven non-diabetic subjects (7 M, 4 F; age 26.5 +/- 6.5 (+/- SD) yr; BMI 21.6 +/- 3.1 kg m-2) followed a high-soluble-fibre (5 g guar gum thrice daily)/low-glucose diet, or a low-soluble-fibre/high-glucose (500 ml glucose drink providing 100 g glucose per day) diet, each for 6 weeks, in randomized order. A 75 g oral glucose tolerance test was performed at recruitment and after each diet period, and fasting blood was assayed for glycosylated albumin by affinity chromatography, and glycosylated haemoglobin by four different methods. Adherence to guar and glucose supplementation was assessed at 89.5 +/- 7.5% and 97.1 +/- 3.5%, respectively. There was no significant effect of either diet on mean fasting, 1-h or 2-h plasma glucose concentration, or glycosylated haemoglobin levels by any assay. Glycosylated albumin was 1.71 +/- 0.35% at entry, fell to 1.33 +/- 0.30% (p less than 0.01) with high-fibre and rose to 1.95 +/- 0.23% (p less than 0.02) after a high-glucose diet. Insulin, total- and HDL-cholesterol and triglyceride levels were unaffected by either diet. A high-glucose diet increases, and a high-soluble-fibre diet decreases, levels of glycosylated albumin without effects on glucose tolerance or glycosylated haemoglobin.

Unexplained variability of glycated haemoglobin in non-diabetic subjects not related to glycaemia

We have studied levels of glycated haemoglobin in a sample of 223 people aged over 40 years without known diabetes mellitus screened in a community study. Each had a glucose tolerance test and glycated haemoglobin measured by four methods - agar gel electrophoresis with and without removal of Schiff base, affinity chromatography and isoelectric focusing. The correlation coefficients between 2 h blood glucose and levels of glycated haemoglobin were between 0.43 and 0.64. This poor correlation was not explained on the basis of assay or biological variability of either 2 h blood glucose or glycated haemoglobin. Multiple regression analysis showed that other assays of glycated haemoglobin contributed to the variance of any single glycated haemoglobin value by 0.1%-52.9% (median 12.8%) compared to the variance of 18.6%-41.4% (median 30.8%) explained by 2 h blood glucose alone, suggesting that in a non-diabetic population, the degree of glucose intolerance may explain only one third of the variance of glycated haemoglobin levels, but other factors operate to produce consistent changes in levels of glycated haemoglobin. Investigation of 42 subjects with consistently high (20 subjects) or low (22 subjects) levels of glycated haemoglobin relative to their 2 h blood glucose level showed no difference in age, gender, body mass index, haemoglobin levels or smoking, although 50% of low glycators had impaired glucose tolerance. Neither ambient blood-glucose levels, as estimated on two five-point blood-glucose profiles, nor dietary intake of carbohydrate, starch, sugars, fibre or alcohol, explained the difference between high and low glycators. The determinants of the consistent interindividual differences in levels of glycated haemoglobin in non-diabetic subjects remain to be determined.

The glycosylated hemoglobin assay for diabetes: its value to the periodontist. Two case reports

The glycosylated hemoglobin assay is a relatively new test used in the diagnosis and monitoring of the diabetic patient. This assay should be of interest to the periodontist as it offers important advantages over traditional blood glucose testing methods. Most importantly, it gives an indication of the blood glucose level over an extended period of time (30 to 90 days), whereas traditional assays only indicate the glucose level at one point in time. Additionally, there is no requirement for fasting prior to testing. Two case reports are presented to illustrate how the glycosylated hemoglobin assay can be utilized by the periodontist.

Clinical utility of serum fructosamine in diabetes mellitus compared with hemoglobin A1c

To evaluate the clinical utility of fructosamine as a mean of monitor glycaemic control, fructosamine and HbA1c were compared in 46 random out-patients visiting a Diabetic Clinic as well as in 25 inpatients admitted to a Diabetes Day Care Unit. In the out-patients, there were a significant correlations between fructosamine and fasting blood glucose (r = 0.75) as well as between fructosamine and HbA1c (r = 0.91). However, when the reference values were considered, interesting differences were found; only 4% of the out-patients showed normal HbA1c values while 39% showed normal fructosamine values. Accordingly, fructosamine and HbA1c evaluate different aspects of glycaemic control. During an admission of 7 days to the Diabetes Day Care Unit no statistical changes in mean blood glucose and fructosamine values occurred. On the other hand, two weeks after discharge from the Unit, not only fructosamine (3.58 +/- 0.16 mmol vs 3.09 +/- 0.08 mmol/l) but also HbA1c (9.52 +/- 0.38% vs 8.33 +/- 0.23%) had improved significantly. Thus HbA1c measures improvements in glycaemic control as early as 3 weeks after changes in treatment. At six weeks after discharge HbA1c (7.63 +/- 0.34%) but not fructosamine (3.02 + 0.14 mmol/l) had improved further. HbA1c is a reliable marker of glycaemic control while the value of fructosamine in clinical practice is unclear.

Glycated haemoglobin and glycated protein and glucose concentrations in necropsy blood samples

Glycated haemoglobin and glycated protein (fructosamine) and blood glucose concentrations were measured in blood samples collected from 75 patients at necropsy. Estimation of blood glucose was a poor indicator of glycaemia before death. Measurement of glycated haemoglobin by affinity chromatography distinguished non-diabetic patients from diabetic patients. The distinction was not as clear cut when HbA1 was estimated using electroendosmosis. Seven patients, who at necropsy had no known history of diabetes, had glycated haemoglobin concentrations in the diabetic range. Two of these patients were found to be diabetic, and diabetes had been suspected at some time in another three patients. It is concluded that measurement of glycated haemoglobin or HbA1, in necropsy specimens is a valuable tool for assessing glycaemic control in known diabetic patients, and may be useful in diagnosing previously unsuspected diabetes.

The glycohaemoglobin assay as a screening test for diabetes mellitus: the Islington Diabetes Survey

Blood glucose 2 h after an oral glucose load (2hBG) and glycohaemoglobin (GHb) (Corning agar-gel electrophoresis) levels were used as screening tests in a general practice diabetic screening programme. The diagnosis of diabetes (DM) was based on a separate oral glucose tolerance test (OGTT) in 223 of 1040 screened subjects, selected as a stratified sample biased towards higher levels of 2hBG and GHb. The GHb assay was also repeated at the recall examination and urine was tested for glycosuria before and after glucose administration. At a cut-off level of 8.1%, the screening GHb assay correctly identified 90% of all probable diabetics with a specificity of 85.3% (95% Cl 83.3-87.3%) and a positive predictive value of 14.0% (9.0-19.0%). The specificity of the screening GHb assay as a screening test for true DM was 45.8% (39.0-52.4%) at 90% sensitivity, and that of the recall GHb assay was 64.5% (57.9-71.1%). The screening 2hBG was 93.3% (88.9-97.7%) specific at 90% sensitivity as a screening test for true DM diagnosed by OGTT at recall. The test characteristics for fasting glycosuria were: sensitivity 16.7% (0-37.8%) and specificity 98.0% (96.0-100.0%). Equivalent values for the post-glucose test for glycosuria were: 72.7% (46.4-99.0%) and 77.4% (70.1-84.7%), respectively. While GHb assay is a poorer screening test for DM than the 2hBG at the single cut-off level quoted, comparison of the accuracy of the two tests shows that the GHb assay is only marginally less accurate. It is superior to testing for glycosuria as a screening test for DM and can be performed on any random blood sample, facilitating its use in population screening.