Undiagnosed Diabetes in US Adults Declines to 11%

Marlene Busko

October 26, 2017

Just over 10% of adults in the United States who have diabetes are not aware of it, new research suggests.

This lower rate of one in 10 is "in stark contrast to previously published national estimates and statements in current clinical practice guidelines, which suggest that one-quarter to one-third of diabetes cases are undiagnosed," say Elizabeth Selvin MD, from the Johns Hopkins University in Baltimore, Maryland, and colleagues, in their paper published online October 24 in the Annals of Internal Medicine.

They explain that the common belief that up to a third of all diabetes cases remain undiagnosed is due to previous estimates from epidemiologic studies that have relied on a single blood test to define hyperglycemia; it is now known that there was high variability among the biochemical tests used to define diabetes.

Hence, the American Diabetes Association (ADA) currently recommends that, in the absence of a clear clinical diagnosis (overt symptoms of diabetes or hyperglycemic crisis), a second blood test is required to confirm the diagnosis of diabetes.

This second test can be from a new blood sample, or it can be two different tests from the same sample — eg, HbA1c and fasting glucose levels — and if the results of the two tests are above clinical thresholds, this also confirms the diagnosis.

The researchers therefore reanalyzed data from the National Health and Nutrition Examination Survey (NHANES), applying these stricter criteria and identified participants who had undiagnosed diabetes — defined as elevated HbA1C and fasting plasma glucose levels — where the second test "confirmed" the diabetes diagnosis.

"When a confirmatory definition is used, undiagnosed diabetes is a relatively small fraction of the total diabetes population," the researchers report. Increased screening by primary-care providers is yielding a bigger proportion of diagnoses and, as such, more opportunities for treatment, they note.

However, there is still room for improvement, they stress. Undiagnosed diabetes was more common in overweight or obese adults, older adults, racial/ethnic minorities (including Asian Americans), and people lacking health insurance or access to healthcare.

"Overall, these findings are encouraging," since they show that there are fewer patients with undiagnosed diabetes than was previously thought, and the numbers are decreasing, says Anne L Peters, MD, from the Keck School of Medicine of the University of Southern California, Los Angeles, in an accompanying editorial.

"In other words, we are actually doing a better job at diagnosing diabetes than was previously appreciated," she notes.

"However, diabetes is still going undiagnosed, particularly in persons who may not have regular access to healthcare or who have several risk factors," she adds. "Thus, public-health efforts to screen at-risk patients and help them receive care may be beneficial."  

Different Diabetes Diagnosis Criteria in Clinical Practice vs Trials

Establishing the burden of undiagnosed diabetes is critical to monitoring public-health efforts related to screening and diagnosis, say Dr Selvin and colleagues.

The Center for Disease Control (CDC), which does not use confirmatory testing, estimates that, using NHANES data, 30.1 million US adults have diabetes, and 23.8% of them (7.2 million) have undisclosed diabetes, without a confirmed diagnosis.

"An inherent incongruity exists between how diabetes is diagnosed in clinical practice and how diabetes cases are identified in epidemiologic studies," Dr Selvin and colleagues explain.

Thus, they reanalyzed NHANES data from 1988–1994, 1999–2002, 2003–2006, 2007–2010, and 2011–2014 to determine rates of confirmed undisclosed diabetes — defined as having elevated levels of HbA1C (> 6.5%) and fasting plasma glucose (> 7 mmol/L [> 126 mg/dL]).

From the earliest years of the study (1988–1994) until the latest years (2011–2014), the prevalence of diabetes in the US population nearly doubled, from 5.5% (9.7 million adults) to 10.8% (25.5 million adults).

During that time, rates of confirmed undiagnosed diabetes increased from 0.89% to 1.2%, but the proportion of undiagnosed diabetes dropped, from 16.3% to 10.9%.

But certain high-risk patients are still not being diagnosed with diabetes, they say.

"Of concern," more than 60% of persons with confirmed undiagnosed diabetes had an HbA1c above 7%, the "usual target" for glycemic control in adults with type 2 diabetes, Dr Selvin and team say.

Moreover, about 65% of younger adults aged 20 to 45 years with confirmed undiagnosed diabetes had HbA1c ≥ 8%.

The study suggests "the presence of a subgroup of overweight and obese adults who lack access to care and are being missed by current screening practices," according to the researchers.

"Ultimately, our results should help inform the allocation of public-health resources and suggest the importance of targeted screening efforts."

Validate One Test With Another to Diagnose Diabetes

For clinicians, says Dr Peters in her editorial, "the results underscore the importance of validating one diabetes test with another to make a diabetes diagnosis in a patient without symptoms."

A single test may be inaccurate, may cause the patient psychological distress, and can change their eligibility for insurance, she observed.

Moreover, a person with only one positive glycemic screening test but with several risk factors (eg obesity, hypertension, family history of diabetes) "still needs risk-factor reduction and closer follow-up."

The results "challenge the established value of 'single-test' estimates of undiagnosed diabetes," she says.

"It makes sense to apply the same standards to diagnosing the national rates of diabetes that we use to diagnose diabetes in our patients.

"These findings suggest that healthcare providers are doing a good job at diagnosing people when they're coming into contact with the healthcare system," Dr Selvin said in a statement.

"It's those people who are not coming into contact with the healthcare system that need to be a focus of our efforts to ensure cases of diabetes are not missed."

Dr Selvin was supported by National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases grant. Disclosures for the coauthors are listed in the article. Dr Peters is on the a dvisory board of Medscape Diabetes & Endocrinology and has no relevant financial relationships.

Ann Intern Med. 2017. Published online October 24, 2017. Abstract, Editorial

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