Diabetes Screening: A1c vs Fasting Plasma Glucose
Among the 3,980 students in sixth grade, a small proportion (3.2%) had hrA1C and a fivefold larger group (16.0%) had IFG. Table 1 shows the association of demographic and baseline physical and metabolic characteristics for normal and high-risk categories of A1C and FPG. hrA1C was associated with a higher prevalence of NH black ethnicity/race, FH of diabetes, BMI, waist circumference, and fasting insulin. Of those with hrA1C, 36.7% had IFG, compared with 15.3% of those with A1C <5.7%. There was no association between A1C and sex, high blood pressure (BP), triglycerides (TGs), or HDL cholesterol.
Table 1 also shows that IFG was associated with male sex, Hispanic ethnicity, BMI, waist circumference, fasting insulin, high BP, and mean TGs, but not FH of diabetes, TGs ≥150 mg/dL, or HDL cholesterol. Among those with IFG, only 7.4% also exhibited hrA1C in comparison with only 2.4% among those with FPG <100 mg/dL.
Table 2 demonstrates the relationship of sixth-grade baseline and eighth-grade end-of-study (EOS) results. Of the 128 students with hrA1C at baseline, 76 (59.4%) had hrA1C and 1 (0.8%) had A1C ≥6.5% at EOS. Of the 635 with IFG in sixth grade, 298 (46.9%) had IFG in eighth grade and 7 (1.1%) had FPG ≥126 mg/dL. Of the 12 youth with evidence of diabetes by A1C or FPG in eighth grade, 4 (33.3%) had A1C ≥6.5% and 11 (91.7%) had FPG ≥126 mg/dL; in sixth grade, among these 12 youth, 1 (8.3%) had hrA1C and 7 (58.3%) had IFG.
Table 3 explores the baseline characteristics of those with persistent (from sixth to eighth grade) abnormalities of A1C and FPG. The sample size becomes small for those with hrA1C at baseline, but in general, there are trends to greater prevalence of baseline risk markers for diabetes in those with persistent elevated A1C as compared with those that revert to A1C <5.7% in eighth grade. The same trends are present for IFG, where the increased sample size contributes to more statistically significant comparisons between those with persistent elevated glucose compared with those who reverted to normal in eighth grade, specifically male sex, BMI, waist circumference, fasting insulin, A1C, and prevalence of high BP, TGs, and HDL, but not prevalence of high-risk race/ethnicity or FH of diabetes.
Table 4 examines the baseline characteristics of the four subgroups defined by both A1C and FPG baseline values: normal for A1C (nA1C) and FPG (NFG), hrA1C with NFG, IFG with nA1C, and hrA1C with IFG. In general the 3,264 sixth graders with nA1C and NFG had the least high-risk characteristics in both sixth and eighth grades. Likewise, the 47 youth with both hrA1C and IFG had the highest rates of FH for diabetes, indices of obesity, waist circumference, and fasting insulin and high BP in sixth grade, and these differences largely persisted in eighth grade. Sixth graders with hrA1C but NFG (n = 81) as compared with those with IFG but nA1C (n = 588) had similar risk markers, although there were significantly greater abnormalities in BMI and obesity (defined by BMI percentile ≥95) but lower fasting insulin. By eighth grade, those with hrA1C but NFG compared with those with IFG but nA1C had statistically significantly greater abnormalities in BMI, BMI z score, obesity, waist circumference, and fasting insulin. Change or persistence in BMI percentile over the study did not have a major effect on the durability of glycemic abnormalities (data not shown).
Results
Among the 3,980 students in sixth grade, a small proportion (3.2%) had hrA1C and a fivefold larger group (16.0%) had IFG. Table 1 shows the association of demographic and baseline physical and metabolic characteristics for normal and high-risk categories of A1C and FPG. hrA1C was associated with a higher prevalence of NH black ethnicity/race, FH of diabetes, BMI, waist circumference, and fasting insulin. Of those with hrA1C, 36.7% had IFG, compared with 15.3% of those with A1C <5.7%. There was no association between A1C and sex, high blood pressure (BP), triglycerides (TGs), or HDL cholesterol.
Table 1 also shows that IFG was associated with male sex, Hispanic ethnicity, BMI, waist circumference, fasting insulin, high BP, and mean TGs, but not FH of diabetes, TGs ≥150 mg/dL, or HDL cholesterol. Among those with IFG, only 7.4% also exhibited hrA1C in comparison with only 2.4% among those with FPG <100 mg/dL.
Table 2 demonstrates the relationship of sixth-grade baseline and eighth-grade end-of-study (EOS) results. Of the 128 students with hrA1C at baseline, 76 (59.4%) had hrA1C and 1 (0.8%) had A1C ≥6.5% at EOS. Of the 635 with IFG in sixth grade, 298 (46.9%) had IFG in eighth grade and 7 (1.1%) had FPG ≥126 mg/dL. Of the 12 youth with evidence of diabetes by A1C or FPG in eighth grade, 4 (33.3%) had A1C ≥6.5% and 11 (91.7%) had FPG ≥126 mg/dL; in sixth grade, among these 12 youth, 1 (8.3%) had hrA1C and 7 (58.3%) had IFG.
Table 3 explores the baseline characteristics of those with persistent (from sixth to eighth grade) abnormalities of A1C and FPG. The sample size becomes small for those with hrA1C at baseline, but in general, there are trends to greater prevalence of baseline risk markers for diabetes in those with persistent elevated A1C as compared with those that revert to A1C <5.7% in eighth grade. The same trends are present for IFG, where the increased sample size contributes to more statistically significant comparisons between those with persistent elevated glucose compared with those who reverted to normal in eighth grade, specifically male sex, BMI, waist circumference, fasting insulin, A1C, and prevalence of high BP, TGs, and HDL, but not prevalence of high-risk race/ethnicity or FH of diabetes.
Table 4 examines the baseline characteristics of the four subgroups defined by both A1C and FPG baseline values: normal for A1C (nA1C) and FPG (NFG), hrA1C with NFG, IFG with nA1C, and hrA1C with IFG. In general the 3,264 sixth graders with nA1C and NFG had the least high-risk characteristics in both sixth and eighth grades. Likewise, the 47 youth with both hrA1C and IFG had the highest rates of FH for diabetes, indices of obesity, waist circumference, and fasting insulin and high BP in sixth grade, and these differences largely persisted in eighth grade. Sixth graders with hrA1C but NFG (n = 81) as compared with those with IFG but nA1C (n = 588) had similar risk markers, although there were significantly greater abnormalities in BMI and obesity (defined by BMI percentile ≥95) but lower fasting insulin. By eighth grade, those with hrA1C but NFG compared with those with IFG but nA1C had statistically significantly greater abnormalities in BMI, BMI z score, obesity, waist circumference, and fasting insulin. Change or persistence in BMI percentile over the study did not have a major effect on the durability of glycemic abnormalities (data not shown).
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