Table 2

A1C levels and incidence of diabetes

CitationA1C cut-off point (or category, or percentiles) %Incidence (95% CI) %Annualized incidence (95% CI) %A1C category (or unit of increase in A1C) %Relative risk (95% CI) (or OR, HR, LR, IR)Notes
Droumaguet 2006(From Figure 1A)After stratifying on FPG, A1C predicted diabetes only in subjects with IFG (FPG ≥ 6.1 mmol/l). The OR for a 1% increase in A1C was 7.2 (95% CI, 3.0–17.0). A1C categories were incorrect on page 1,622. The correct ones are 4.5–5.0, 5.1–5.5, 5.6–6.0, and 6.1–6.5 (confirmed by authors)
Women:6-year cumulativeWomen:
5.3–5.70.40.1
5.85.00.9
5.8–7.111.01.9<4.5OR (95% CI), ref.
Men:6-year cumulativeMen:4.5–5.00.9 (0.5–1.5)
5.3–5.72.60.45.1–5.51.5 (0.7–3.4)
5.85.00.95.6–6.05.0 (2.0–12.8)
5.8–7.111.52.06.1–6.532.7 (11.5–92.6)
Edelman 2004≤5.5Annual, 0.8 (0.4–1.2)0.8 (0.4–1.2)Obese patients with A1C 5.6 to 6.0 had an annual incidence of diabetes of 4.1% (95% CI, 2.2–6.0%)
5.5–6Annual, 2.5 (1.6–3.5)2.5 (1.6–3.5)
6.1–6.9Annual, 7.8 (5.2–10.4)7.8 (5.2–10.4)
(From Figure 2)(From Figure 2)(From Figure 2)IR*
5.1–5.50.9 (SEM, 0.5)0.9 (SEM, 0.5)1.0
5.6–6.02.5 (1.0)2.5 (1.0)2.8
6.1–6.56.4 (2.5)6.4 (2.5)7.1
6.6–6.918.0 (12.0)18.0 (12.0)NR20.0
Hamilton 2007Baseline mean A1C for those with incident diabetes is 6.3 (0.7), and for nondiabetes is 5.2 (0.4)
6-year cumulative
5.6 in baseline37.06.2NRNR
Inoue 2007<5.8 with high NFGAnnual, 0.90.9FPG and A1C predicts incidence of diabetes, especially for those with FPG ≥ 5.55 mmol/l
≥5.8 with high NFGAnnual, 3.33.3
<5.8 with IFGAnnual, 2.52.50.5% increase in A1COR (95%CI)
≥5.8 with IFGAnnual, 9.59.53.0 (1.7–5.3)
Ko 2000LRThe calculation of annual incidence diabetes for category of A1C < 6.1 with FPG > 6.1 mmol/l is incorrect (44.1). The correct one is 54.1 (confirmed by authors)
<6.1 with FPG <6.1Annual, 8.18.1<6.1 with FPG <6.10.6
≥6.1 with FPG <6.1Annual, 13.713.7≥6.1 with FPG <6.10.9
<6.1 with FPG ≥6.1Annual, 17.417.4<6.1 with FPG ≥6.11.1
≥6.1 with FPG ≥6.1Annual, 54.154.1≥6.1 with FPG ≥6.19.3
Kolberg 20095-year cumulativeBaseline mean A1C for those with incident diabetes is 6.1 (0.1), and for nondiabetes is 5.9 (0.1). No-converters were randomly selected in a 3:1 ratio to converters. We calculated incidence of diabetes using data from whole sample
6.0 in baseline5.71.2NRNR
Lee 2002Women:4-year cumulativeWomen:Women:IRThe overall 4-year incidence rate was 19.7% among 1,664 participants without diabetes in baseline, and average annual Incidence rate 4.9%
120: <5.127.46.9120: <5.11.0
98: 5.1–5.434.78.798: 5.1–5.41.3
121: ≥5.547.912.0121: ≥5.51.7
Men:4-year cumulativeMen:Men:IR
59: <5.230.57.659: <5.21.0
50: 5.2–5.532.08.050: 5.2–5.51.0
56: ≥5.651.813.056: ≥5.61.7
Little 19943.3-year cumulativeA1C was classified as either normal or elevated based on whether it was below or above the upper limit of the A1C normal range (6.03%)
≤6.03 with NGT9.72.9
>6.03 with NGT11.13.4
≤6.03 with IGT27.78.41.0% difference in A1COR (95% CI)
>6.03 with IGT68.420.76.8 (1.8–25.8)
Narayan 199625th percentiles, 5.75-year cumulative25th percentiles, 5.7HR (95% CI)The diabetes hazard rate ratio (95% CI) is 1.8 (1.5–2.1) as predicted by A1C percentiles of 25th and 75th.
75th percentiles, 6.713.51.675th percentiles, 6.71.8 (1.5–2.1)
Median (25th–75th percentiles)Median (25th–75th percentiles)
5.5 (5.2–5.9) for5.5 (5.2–5.9) for
    no-converters    no-converters
Nijpels 19965.7 (5.3–6.0) for3-year cumulative5.7 (5.3–6.0) forNRThe incidence density of diabetes was 13.8% per year (95% CI, 3.5–24.0). At baseline, 12% (n = 19) of subjects had A1C > 6.1% of whom 52.6% progressed to diabetes
    converters28.5 (15.0–42.0)9.5    converters
Norberg 2006Mean time of 5.4+/−8.4 year cumulativeThe combination of A1C, FPG, and BMI are effective for predicting risk of diabetes
WomenWomenWomen
<4.518.13.4OR for women, ref.
4.5–4.6935.96.6<4.5
≥4.764.311.94.5–4.692.0 (0.5–8.9)
MenMenMen≥4.719.6 (2.5–152.4)
<4.515.32.8<4.5OR for men, ref.
4.5–4.6944.48.24.5–4.691.2 (0.3–5.3)
≥4.773.213.6≥4.716.0 (2.2–115.3)
Pradhan 2007<5.0Annual, 0.10.1<5.0RR (95%CI), ref.For diabetes, an increase in risk was noted in each category above 5.0% in both age-adjusted and multivariable models and after exclusion of cases diagnosed with 2 years or even 5 years of follow-up
5.0–5.4Annual, 0.50.55.0–5.44.1 (3.5–4.9)
5.5–5.9Annual, 3.23.25.5–5.925.6 (21.1–30.8)
6.0–6.4Annual, 9.19.16.0–6.476.7 (59.4–99.1)
6.5–6.9Annual, 9.39.36.5–6.977.6 (51.4–117.4)
≥7.0Annual, 22.722.7≥7.0201.4 (149.7–271.1)
Preiss 2,0092.8-year cumulativeA1% increase in A1COR (95%)Baseline mean A1C for those with incident diabetes is 6.8 (0.9), and for nondiabetes is 6.2 (0.7)
6.2 (0.7) in baseline7.82.82.3 (1.9–2.8)
Sato 20094-year cumulativeEven after stratifying participants by FPG (≤ 99 or ≥ 100 mg/dl), elevated A1C had an increased risk of type 2 diabetes
≤5.33.00.7≤5.3OR (95%), ref.
5.4–5.76.51.65.4–5.72.3 (1.7–3.0)
5.8–6.220.65.15.8–6.28.5 (6.4–11.3)
6.3–6.741.910.56.3–6.723.6 (16.3–34.1)
≥6.869.117.3≥6.873.3 (41.3–129.8)
Shimazaki 20073-year cumulativeTotal sample size is 38,628 with age range from 15 year above. Tables 3 and 4 reported a subgroup of middle-aged data
<5.60.2 (0.1–0.3)0.1
5.6–6.47.5 (3.6–15.7)2.55.6–6.4HR (95% CI), ref.
≥6.530.8 (21.7–43.8)10.3≥6.57.1 (4.6–10.9)
Yoshinaga 19965-year cumulativeIR*The combination of A1C and OGTT enables more precise prediction of progression to diabetes in those with glucose intolerance
≤6.35.41.1≤6.31.0
6.4–6.720.34.16.4–6.73.7
≥6.852.110.4≥6.89.5
  • *Incidence ratio (IR) was computed by the incidence in each A1C category divided by the incidence of the lowest A1C category. FPG, fasting plasma glucose; HR, hazard ratio; IFG, impaired fasting glucose; IGT, impaired glucose tolerance; IR, incident ratio; LR, likelihood ratio; NFG, normal fasting glucose; NGT, normal glucose tolerance; NR, nor reported; OGTT, oral glucose tolerance test; OR, odds ratio; ref., reference; RR, relative risk.