Repeat testing necessary for accurate hyperglycemia screening
medwireNews: Testing both glycated hemoglobin (HbA1c) and fasting plasma glucose (FPG) gives a more reliable hyperglycemia diagnosis than either on its own, but a follow-up screening test remains essential, say researchers.
The study also found HbA1c alone to be a more reliable indicator than FPG alone of whether people would still have nondiabetic hyperglycemia when retested a median of 40 days after their initial positive test, or whether the diagnosis would change to normoglycemia or to type 2 diabetes.
Researcher Max Bachmann (University of East Anglia, Norwich, UK) and colleagues looked at data from 10,000 participants of the Norfolk Diabetes Prevention Study, focusing on 2208 who had nondiabetic hyperglycemia according to HbA1c (42–47 mmol/mol; 6.0–6.4%), FPG (≥5.6 or 6.1 to <7.0 mmol/L), or both measures at their initial test.
At repeat testing, nondiabetic hyperglycemia based on HbA1c level was confirmed in 68.3% of people whose initial diagnosis was based on HbA1c, in 24.0% of those with a FPG diagnosis, and in 74.3% of those with both.
A corresponding 26.6%, 46.6%, and 17.0% reverted to a diagnosis of normoglycemia, whereas 5.1%, 29.4%, and 8.8% shifted to a diagnosis of type 2 diabetes.
There was a similar pattern among people with an initial type 2 diabetes diagnosis, with the likelihood of having the diagnosis confirming being markedly higher for an initial HbA1c test than an FPG test, but highest of all for both. However, people with an initial type 2 diabetes diagnosis were unlikely to revert to a normoglycemia diagnosis, with rates ranging from 0.0% to 13.1% depending on the initial test.
“Because HbA1c and FPG are known to vary randomly within individuals over time, it was predictable that individuals found to have high glucose or HbA1c levels on initial testing would tend to have lower levels on retesting, because of regression to the mean,” write the researchers in Diabetic Medicine.
In line with this, higher baseline HbA1c was associated with a larger decrease in HbA1c by the time of the second test.
“The results of this study show that, to increase certainty that participants in screening truly have Type 2 diabetes or non-diabetic hyperglycaemia that is not transient, it is desirable to repeat the test,” say Bachmann and team.
And they add that “clear policies are needed for management of individuals with discordant test results.”
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