A number of medications interfere with results, diuretics, niacin
, contraceptives, and more. There are no standards related to aging, and results have not been as reliable.
Charting the fasting glucose is the way to go now.
A reading of over 126 of course wouldn't require a challenge test anyhow, the diagnosis of diabetes would be obvious.
No endocrinologist worth his money, is watching a patients fasting glucose continue rising between 100-126, without sounding the alarm bells.