Glucose Meters Can Give Inaccurate Readings

That kind of inaccuracy is concerning, researchers say, because small differences in blood sugar during pregnancy can have potentially serious consequences for the mother and baby. 

But that doesn't mean women should stop using glucose meters. Instead, they should pay more attention to getting the readings right. 

Dr. David Sacks, who heads the clinical chemistry lab at the National Institutes of Health, said that, people with diabetes often rely on the devices as convenient indicators of when to take insulin and how much they need. 

"They're very small, you can put them in your pocket," said Sacks, who was not involved in the new work. "You can prick your finger and get the result immediately. But the meters have never been as accurate as blood that's drawn in central labs." 

To test just how accurate they really are, Dr. Nimalie Perera, of the Royal Prince Alfred Hospital in Sydney, Australia, compared readings from 102 women to a more precise lab test. 

The women all had diabetes -- most of them gestational diabetes, which begins during pregnancy -- and came to a prenatal clinic for nurses to measure their blood sugar levels. For each patient, nurses drew blood with a finger prick using six different glucose meters. 

The most accurate model, StatStrip® Hospital Glucose Monitoring System, was off from the lab result by an average of 6 percent, according to findings published in Diabetes Care. The least accurate, Optium Xceed by Medisense was off by almost 16 percent. Both are available in the U.S. 

The U.S. Food and Drug Administration has to approve all devices that are marketed for medical conditions in the country. Recently, Sacks says, the FDA has been trying to improve standards to increase the accuracy of blood glucose meters. 

Three of the glucose meters tested, including the Optium Xceed, are made by Abbott Diabetes Care and meet the current international standard for blood glucose meter accuracy. 

Both U.S. and Australian standards committees recommend that glucose meters should give results within 20 percent of laboratory tests, but researchers say that may not be good enough, especially for pregnant women with diabetes. 

Dr. Boyd Metzger, who studies diabetes in pregnancy at Northwestern University, stated that, "When it's not treated correctly, diabetes during pregnancy can lead to a higher risk of miscarriage or a more difficult birth and heavier newborns." Because of that, the goal is "to bring the blood glucose levels of (pregnant women) with diabetes as close to normal as can be achieved." However, he added, "that's led to a lot of dependence on self-monitoring." 

Meters also store the readings, so that doctors can track patients' diabetes -- and how well they are managing it with insulin and meals -- every time they go in for an appointment. If the measurements are inaccurate, women may give themselves doses of insulin that are higher or lower than what they should be receiving, or doctors may not have the best information to counsel and treat their patients. And using the devices isn't straightforward either, said Metzger, who was not involved in the current study. 

"We give them a meter and teach them how to do it and then try to use that information (from the meter) right away," he said. "There's a significant learning curve for ... this kind of technology." 

Sacks said the new study may underestimate the problems with glucose meters, because all the readings were done by trained nurses, which is very different from when patients use them for the first time. Women may also be hesitant to redo a measurement even if they worry it could be wrong, because the strips they are done on cost about 60 cents each. The meters themselves start at around 15 dollars. 

Despite the inaccuracies, Sacks said the meters are still the best tool there is to manage diabetes on a day-to-day basis. "What pregnant women should do is follow the directions very, very carefully," he said. "Make sure that the technique is as good as can be." And if something seems off, such as a low reading right after a big meal, "they should repeat the test," he advised.