medwireNews: Study findings highlight the importance of carrying out two tests of glycemia to confirm a diabetes diagnosis and suggest that previous estimates of undiagnosed cases based on single measures may have overstated the prevalence.
“A common belief is that one quarter to one third of diabetes cases in the United States are undiagnosed,” say Elizabeth Selvin (Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA) and colleagues.
But these previous national estimates have been based on a single measure of glycemia – fasting plasma glucose, glycated hemoglobin (HbA1c), or oral glucose tolerance test, they note.
When the researchers used a test combining fasting plasma glucose (≥7.0 mmol/L) and HbA1c (≥6.5%), they found that, while the prevalence of total diabetes (diagnosed plus undiagnosed) has increased over time, the percentage of those with undiagnosed diabetes as a proportion of total cases has decreased, from 16.3% in 1988–1994 to 10.9% in 2011–2014.
“When a confirmatory definition is used, undiagnosed diabetes is a relatively small fraction of the total diabetes population; most US adults with diabetes (about 90%) have received a diagnosis,” they comment in the Annals of Internal Medicine.
The researchers reanalyzed data from NHANES III (1988–1994) and the continuous NHANES (1999–2014) survey, which releases data in 2-year cycles, for a total of 24,430 individuals aged at least 20 years. Prevalence estimates from these different surveys were then applied to the US Census population numbers to estimate the number of people with diagnosed and confirmed undiagnosed diabetes in the USA.
The prevalence of total diabetes increased “substantially” from 5.5% (9.7 million adults) in 1988–1994 to 10.8% (25.5 million adults) in 2011–2014.
Confirmed undiagnosed diabetes also increased on an absolute scale, from 0.89% in 1988–1994 to 1.17% in 2011–2014, but decreased as a proportion of total diabetes cases during this period.
“Our analysis demonstrates that we are doing a better job with diabetes screening and diagnosis than might be inferred from previous estimates,” say Selvin and colleagues.
In a related editorial, Anne Peters, from the University of Southern California in Los Angeles, USA, says the findings underscore the “importance of validating one diabetes test with another to make a diabetes diagnosis in patients without symptoms.”
But noting that glucose levels exist in a continuum, she recommends addressing risk factors and close follow-up for individuals with several risk factors even if they only test positive on one measure.
The most common risk factors were obesity, affecting 90% of those with undiagnosed diabetes, and older age, along with male sex, being of Black, Mexican American or Asian American ethnicity, and having low healthcare access.
The associations between these risk factors and undiagnosed diabetes were stronger with the confirmed definition than with single-test measures, which the researchers say suggests “the presence of a subgroup of overweight and obese adults who lack access to care and are being missed by current screening practices.”
By Lucy Piper
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