Those participants in the intensive-therapy group who entered the study with no signs of retinopathy and very low to no protein in the urine had a 76% reduction in progression to retinopathy compared with those in the conventional treatment group. Even people with mild to moderate retinopathy and microalbuminuria (very small quantities of albumin in the urine) benefited from intensive therapy, seeing a 54% reduction in retinopathy progression. Even if you haven’t met your HbA1c goal yet, you might be pleased to know that just about any decrease in blood glucose levels can help. The study found that every decrease of 10% of one’s HbA1c was linked to a 39% decrease in risk of retinopathy.
Diabetic neuropathy was reduced by 60% in the intensive-treatment group compared with the conventional treatment group.
Type 2 diabetes. The DCCT’s findings about the link between HbA1c levels and risks for complications in people with Type 1 diabetes were complemented by similar findings in another large study—this one of people with Type 2 diabetes—called the United Kingdom Prospective Diabetes Study (UKPDS). The UKPDS studied over 4500 people with Type 2 diabetes, assigning them to receive either a diet-based treatment regimen or a more intensive regimen utilizing a sulfonylurea (a class of diabetes pills that stimulate the pancreas to produce more insulin), metformin, or insulin. Those people treated with diet achieved average HbA1c levels of 7.9%, while those on the more intensive regimen attained an average HbA1c of 7.0%. The study found that there was a direct relationship between HbA1c levels and risks for some diabetes complications; people with lower blood glucose levels had lower risks of microvascular (small blood vessel) complications such as retinopathy, neuropathy, and nephropathy.
For every percentage point decrease in HbA1c (say, from 11% to 10%), there was a corresponding 37% decrease in microvascular complications and a 21% decrease in deaths related to diabetes.
“DCCT-comparable.” When HbA1c tests were first introduced, different laboratories used different methods to compute HbA1c levels. The multitude of methods lead to different results being reported—a result above, say, 8%, which would indicate high blood glucose levels in a DCCT participant, might represent normal blood glucose levels at some laboratories. People who switched physicians or physicians who changed the laboratory to which they sent their samples had to be careful about interpreting HbA1c results.
To reduce confusion and to make HbA1c results readily comparable with the results of the DCCT, the National Glycohemoglobin Standardization Program (NGSP) was begun to certify labs and their testing methods. Most HbA1c tests done by laboratories in the United States today are performed using methods certified by the NGSP as being standardized to DCCT results.
The ADA recommends routine checking of HbA1c levels. Exactly how often yours should be checked depends on your degree of blood glucose control and your physician’s judgment. Because the HbA1c test is an indicator of blood glucose control over the previous 2–3 months, people who are having trouble meeting their goals or people whose medicine, diet, or exercise regimens have changed may be helped by having HbA1c assessments every three months. Many experts recommend having the HbA1c test at least twice a year for people who are meeting their blood glucose control goals.
In some cases, your physician may decide to order more frequent HbA1c tests. Very large changes in your average blood glucose level can be reflected in your HbA1c in about two weeks, so a person who’s been newly diagnosed may have HbA1c tests every few weeks while his initial therapy is adjusted. Pregnant women with diabetes may also have their HbA1c monitored every month or every two months to help them achieve the tight blood glucose control recommended to prevent health problems for the fetus. (See “The Fructosamine Test” for more information on a related test sometimes recommended for pregnant women for gauging long-term blood glucose control.)