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Two Standard Blood Tests May Get an Overhaul
August 10, 2007
Findings from three recent studies may soon cause the way two important blood tests are administered or interpreted to change. Researchers studying the relationship between after-meal triglyceride levels and heart risk and the accuracy of the HbA1c test have concluded that there may be better ways to measure or present results from these tests.
First, two studies looking at the relationship between triglyceride levels and risk of heart attack or other cardiovascular “events” had some surprising results. While blood tests checking people’s triglyceride levels are usually administered after a 12- to 14-hour fast, both studies found that high triglyceride levels in the hours immediately following a meal are much more closely linked to a person’s cardiovascular risk. Both studies were published in The Journal of the American Medical Association on July 18.
The first study, which followed about 14,000 Danish people for an average of 26 years, found that women with the highest levels of triglycerides in their blood in the hours after a meal had about five times the risk of dying from a cardiovascular event than those with the lowest levels. Men with the highest levels had twice the risk of men with the lowest levels.
The second study, performed by researchers from Harvard University, followed about 25,000 participants in the Women’s Health Study for more than 11 years. In this study, women who had the highest triglyceride levels two to four hours after a meal had a 44% increased risk of a cardiovascular event. What’s more, the risk went down as time passed after the meal, and ultimately women with high triglyceride levels four hours or later after eating did not show any increased risk of cardiovascular problems. In other words, the participants’ triglyceride levels right after eating were a much better predictor of heart risk than their “fasting” levels hours later.
The results of these two studies may ultimately lead to a change in the timing of routine triglyceride blood tests.
In other news, an ongoing study has been looking at how well the HbA1c test corresponds to a person’s average blood glucose level. Preliminary results were presented in June at the American Diabetes Association’s 67th Annual Scientific Sessions, and if the completed study confirms early findings, people with diabetes may soon have their HbA1c results reported not as a percentage, but in “average glucose (AG) units.”
The study, which is being conducted at 10 venues around the world, plans to look at 700 volunteers: 300 with Type 1 diabetes, 300 with Type 2 diabetes, and 100 without diabetes. It will measure participants’ HbA1c levels regularly and also measure their average blood glucose levels with a combination of continuous glucose monitoring technology and fingersticks.
Results from the first 250 subjects have shown that people’s HbA1c values, which measure the percentage of the blood’s hemoglobin molecules that have glucose attached to them, are closely correlated to their average blood glucose values. If this correlation is confirmed by the larger study, doctors will be able to use the HbA1c test to report people’s average glucose values in milligrams per deciliter (mg/dl), the same units people use when monitoring their blood glucose levels at home. The test itself would not change, but the presentation of its results would be different. The new number may be called the “A1c derived average glucose,” or ADAG.
Full results from this study should be available this September. Some experts believe that an average glucose level will be easier for people with diabetes to understand and discuss with their doctors than an HbA1c percentage. The American Diabetes Association currently recommends that people with diabetes aim for an HbA1c under 7% in general and as close to normal (under 6%) as possible.
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