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Capillary blood glucose test beats HbA1c for mass diabetes screening

Reuters Health • The Doctor's Channel Daily Newscast

NEW YORK (Reuters Health) – As a mass screening tool for diabetes and pre-diabetes in China, the fasting capillary blood glucose (FCG) test performs better than the hemoglobin A1C (HbA1c) test, a study suggests.

“We have evaluated the performance of HbA1c as a mass screening test for diabetes and pre-diabetes in a general Chinese population with a wide spectrum of glucose levels,” Dr. Qing Qiao from University of Helsinki, Finland, who was involved in the study, noted in an email to Reuters Health.

“We showed the performance of HbA1c is inferior to the performance of the FCG test for detecting undiagnosed diabetes, and not an adequate test for pre-diabetes defined according to both fasting and/or 2-hour plasma glucose criteria,” the researcher said.

The findings are based on data from 2332 Chinese individuals (986 men and 1346 women) aged 35 to 74 years who participated in a population-based cross sectional survey of diabetes in Qingdao, China.

For the survey, a 2-hour 75-gram oral glucose tolerance test (OGTT) was used to diagnose diabetes. The performance of the HbA1c and FCG tests were evaluated against the OGTT results by using receiver operating characteristic curve (ROC) analysis.

According to the investigators, the prevalence of newly diagnosed diabetes and pre-diabetes (impaired fasting glucose and/or impaired glucose tolerance) were 11.9% and 29.5%, respectively.

“The high prevalence of diabetes observed in this study reflects the recent increase in the prevalence of diabetes in Qingdao,” the authors note in the December 10th online issue of Diabetes Care.

They further note that the area under the ROC curve was lower for HbA1c than for FCG for detecting new diabetes (0.67 vs 0.77, p < 0.01, in men; and 0.67 vs 0.75, p < 0.01, in women) and pre-diabetes ( 0.47 vs 0.64, p < 0.001, in men; and 0.51 vs 0.65, p < 0.001, in women).

In this study population, the optimal HbA1c cut off point for newly diagnosed diabetes was 5.6%, which is lower than the recommended value of 6.5% or greater.

Less than 30% of new diabetes cases could be identified at the HbA1c cut off point of 6.5% or greater, the researchers found.

At the 5.6% HbA1c cut point for newly diagnosed diabetes, the sensitivity was 64.4% in men and 62.3% in women, whereas it was 72.0% in men and 65.1% in women at the optimal FCG cut off points of 6.3 mmol/L for men and 6.6 mmol/L for women.

“Considering its high cost and poor performance, the HbA1c test is not a suitable test for mass screening, particularly with the purpose of detecting pre-diabetes for early intervention,” the authors conclude.

“The study does not exclude the utility of the HbA1c test in a clinical setting,” Dr. Qiao emphasized in an email to Reuters Health.

Diabetes Care 2009.