Why measure HbA1c?
Why measure HbA1c?
HbA1c has gained acceptance as an accurate index of long-term blood glucose control. Longitudinal studies have shown that good metabolic control, reflected by stable HbA1c level can prevent or postpone micro- and macrovascular and other complications or slow down the progress of such complications in both Type 1 and Type 2 diabetics. The Diabetes Control and Complications Trial (DCCT), and the United Kingdom Prospective Diabetes Study (UKPDS), clearly demonstrated that there is a good correlation between glycemic control and the incidence of late complications.
In this study of 1,141 patients with Type 1 diabetes, with or without complications at baseline, the mean HbA1c values over the nine-year study period were 7.2% with intensive therapy and 9.1% in the conventional group. Even more important; late complications were rarer in the group with lower HbA1c treated intensively. The results showed that intensive treatment with lower and more stable HbA1c values delayed the onset or slowed the progression of clinically important retinopathy, including vision-threatening lesions, nephropathy and neuropathy by 35% to more than 70%. The study established HbAc1c as the gold standard of glycemic control, with levels £7% deemed appropriate for reducing the risk of vascular complications in diabetic patients. In another longitudinal study: the Barbados Eye Study, 324 diabetic patients at risk for developing diabetic retinopathy was followed-up for 9 years. Diabetic retinopathy risk increased with 30% for each increase of HbA1c of 1%.
In the UKPDS, a study of over 4,000 patients with newly diagnosed Type 2 diabetes, treated with different regimens, a 1% reduction of HbA1c was associated with a 35% reduction in macrovascular endpoints, an 18% reduction in myocardial infarction, and a 17% reduction in all-cause mortality. Also in this study there was a correlation between HbA1c values obtained and the rate of complications. Over the 10-year study period, the average HbA1c was 7.0% in the intensively treated group compared with 7.9% in the conventional group. The benefit of intensive treatment appeared to be independent of type of treatment. The EURODIAB study conducted in 31 European centres, that followed HbA1c in 3,250 patients with Type 1 diabetes, found that HbA1c was a predictor for the development of retinopathy and neuropathy, and also for worsening of albuminuria.
It was recently reported from the Atherosclerosis Risk in Communities Study that raised HbA1c could be an independent risk factor for stroke with similar relative risk as for coronary heart disease, and not only in diabetics, but also in adults without diabetes. The study included 10,886 participants without diabetes and 1,635 with diabetes that were followed up for 8-10 years. It is also interesting that a significant joint effect of HbA1c and another risk factor for vascular disease, C-reactive protein (CRP) were found on the atherosclerotic progression in both diabetic as well as non-diabetic subjects in a population-based German study of 3,534 persons followed for 2 years.
Most of the cost of diabetes - in suffering, in lost years of working capacity, and in health care - comes from its complications.
Efficient glucose control and monitoring using HbA1c can thus reduce diabetes complications efficiently.
Interpretation of HbA1c
Although the glycohemoglobin value reflects the average blood glucose levels over the previous 2-3 months, it is not possible to logistically determine the precise mathematical relationship between a particular glycohemoglobin level and mean plasma glucose. Several studies have shown that the closer the glycohemoglobin level is to normal range, the lower is the mean plasma glucose value. Ideally, an important diabetes care goal would be to maintain glycohemoglobin levels in the non-diabetic range. It must be determined, however, if such a goal is realistic.
The outcome of the Diabetes Control and Complications Trial (DCCT study) has been and is important concerning treatment of Type 1 diabetes mellitus. The goal for the participants receiving intensive therapy was HbA1c levels <6.05%. 44% of the patients receiving intensive therapy achieved the goal of glycated hemoglobin value of 6.05% or less at least once during the study. Less than 5% maintained an average value in this range.
The recommendation from the DCCT study is that most patients with Type 1 diabetes should be treated with closely monitored intensive regimens, with the goal of maintaining the glycemic status as close to the normal range as safely possible. Because of the risk of hypoglycemia, intensive therapy should be implemented with caution.
