Clinical Data

Race, ethnicity, education, general health, smoking, and past medical history were defined by self-report. Medications were inventoried with assistance from electronic health records. Many participants used multiple glucose-lowering medications; all participants studied were required by design to use insulin, a sulfonylurea, or both. Insulin usage was categorized by type of insulin, frequency of dosing, and duration of effect: long- or intermediate-acting only, mixed insulin (a combination of intermediate- and short-acting insulin), basal bolus (use of a long- or intermediate-acting plus a separate short-acting insulin), or no insulin. The mean of two eGFR measurements was calculated from creatinine (measured at two separate study visits) traceable to isotope dilution mass spectrometry (IDMS) using the CKD Epidemiology Collaboration equation (19). Hemoglobin A1c was measured by HPLC at the University of Missouri, conforming to National Glycohemoglobin Standardization Program (NGSP) standards, from whole blood collected at the end of each CGM period; the mean of the two values was used for analyses. During CGM, participants were asked to keep a log of medication use, physical activity, and meals, although logging was not strictly enforced and most logs appeared incomplete.