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Screening with Hb[A.sub.1c] often missed diabetes.


SAN DIEGO -- Slightly more than half of veterans targeted for screening have unrecognized diabetes or prediabetes, results from a recent analysis showed.

However, screening such patients by measuring hemoglobin Ale "would result in major misclassification--missing disease when it is present and, to a lesser extent, mislabeling normals as having disease," Sandra L. Jackson, M.P.H., said at the meeting.


The findings are based on a study of 789 individuals from the Atlanta VA Medical Center that assessed the use of targeted screening to detect prediabetes and diabetes, and to compare Hb[A.sub.1c] testing with the oral glucose tolerance test (OGTT), said Ms. Jackson, a graduate student in the nutrition and health sciences doctoral program at Emory University, Atlanta.

Although screening to detect unrecognized diabetes and prediabetes is recommended, the best strategy for screening in primary care settings is unknown. The upside of the OGTT, Ms. Jackson said, is that it's established in clinical use, it can detect all patients with prediabetes, "and the glucose measurement itself is accurate. On the downside, it requires [fasting] and morning testing. It's burdensome for patients and health care systems, and it has poor day-to-day reproducibility."

The upside of Hb[A.sub.1c], she said, is that it does not require a fast, "and it's only a single blood draw, so it's much more convenient, there's less day-to-day variation, and there's greater preanalytic stability. On the downside, measurement may be problematic as platforms vary, point-of-care testing can be unreliable, there's a lack of agreement on cutoffs, and there may be racial and age disparities such that blacks and older persons may have higher Hb[A.sub.1c] independent of glucose."

The researchers defined hyperglycemia according to American Diabetes Association criteria: prediabetes as a fasting OGTT of 100-125 mg/dL or a 2-hour OGTT of 149-199 mg/dL, and diabetes as a fasting OGTT of 126 mg/dL or greater or a 2-hour OGTT of 200 mg/dL or greater.

They categorized Hb[A.sub.1c] results according to three sets of diagnostic criteria: the International Expert Committee (IEC) (prediabetes 6.0%-6.4%, diabetes 6.5% or greater), ADA (prediabetes 5.7%-6.4%, diabetes 6.5% or greater), and the Department of Veterans Affairs / Department of Defense (VA/DoD) (prediabetes 5.7%-6.9%, diabetes 7.0% or greater).

The mean age of the 789 study participants was 58 years, 95% were men, 74% were black, and their mean BMI was 30.5 kg/[m.sup.2].

Screening was offered to patients meeting National Institutes of Health guidelines for screening: without known diabetes, and with age greater than 45 years or a BMI of more than 25 with another risk factor.

Fully 10% of patients met criteria for diabetes based on the OGTT, a higher rate compared with the Hb[A.sub.1c] guidelines (6.7% by the IEC, 6.7% by the ADA, and 1.5% by the VA/DoD guidelines, respectively). "This would indicate that these cutoffs are insensitive compared with the OGTT for detecting diabetes," she said.

According to the OGTT, 42% had prediabetes: 27% had isolated impaired fasting glucose, 6% had isolated impaired glucose tolerance, and 9% had both.

In patients with diabetes by OGTT criteria, Hb[A.sub.1c] classification by IEC criteria labeled 32% correctly, 38% incorrectly as having prediabetes, and 29% incorrectly as being normal; ADA criteria labeled 32% correctly, 50% incorrectly as having prediabetes, and 18% incorrectly as being normal; and VA/DoD criteria labeled 12% correctly, 71% incorrectly as having prediabetes, and 18% incorrectly as being normal.

In patients with prediabetes by OGTT criteria, Hb[A.sub.1c] classification by IEC criteria labeled 36% correctly, 6% incorrectly as having diabetes, and 59% incorrectly as being normal; ADA criteria labeled 61% correctly, 6% incorrectly as having diabetes, and 33% incorrectly as being normal; and VA/DoD criteria labeled 66% correctly, 1% incorrectly as having diabetes, and 33% incorrectly as being normal.

The prevalence of diabetes increased in a stepwise fashion with increasing BMI, from 1.5% among those with a normal BMI (18.5-24.9) to 15% among those who met criteria for class III obesity (BMI more than 40). "'For every I unit increase in BMI, we observed a 10% increase in the odds of having diabetes," she said.

Ms. Jackson also reported that with the IEC, ADA, and VA/DoD cutoffs for diabetes, screening with Hb[A.sub.1c] was specific but insensitive, with a false negative rate of 68% at the 6.5% cutoff and a false negative rate of 89% at the 7.0% cutoff.

The study was supported by a grant from the VKs Health Services Research and Development Service. Ms. Jackson said she had no conflicts of interest.
Hb[A.sub.1c] Categorized by Three Sets of Diagnostic Criteria

Patients with
diabetes by
OGTT criteria

           Diabetes labeled    Diabetes labeled   Patient incorrectly
           correctly           incorrectly as      diagnosed as normal

IEC            32%                  38%                    29%
ADA            32%                  50%                    18%
VA/DoD         12%                  71%                    18%

Patients with
prediabetes by
OGTT criteria

IEC            36%                   6%                    59%
ADA            61%                   6%                    33%
VA/DoD         66%                                         33%

Note: Based on a study of 789 individuals. Figures have been rounded.

Source: Ms. Jackson

Note: Table made from bar graph.
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Author:Brunk, Doug
Publication:Family Practice News
Date:Aug 1, 2011
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