Predicting type 2 diabetes mellitus using haemoglobin A1c: A community-based historic cohort study

Figures & data

Figure 1. Study flow chart. ^aLoss to follow up due to death or transfer from CHS.

Table 1. Baseline characteristic of the cohort.

	n	%
Total	10 201	100
Male gender	4593	45.0
Low socio-economic status	2285	22.4
Hypertension	1640	16.1
Peripheral vascular disease	25	0.2
Ischaemic heart disease	245	2.4
Cardiovascular diseases^a	1820	17.8
BMI > 25 (kg/m^2) (n = 8747)^b	6718	76.8

BMI, body mass index.

^aHypertension, ischaemic heart disease or peripheral vascular disease.

^bMissing data – 1454 patients (14.3% of the total cohort).

Table 2. Distribution of HbA1c values in the study cohort (n = 10 201).

HbA1c sub-group	HbA1c values	n	% of Total cohort
Reference	HbA1c < 4.5%	166	1.63
1	4.5% ≤ HbA1c < 5.0%	1013	9.93
2	5.0% ≤ HbA1c < 5.5%	3064	30.04
3	5.5% ≤ HbA1c < 6.0%	3452	33.84
4	6.0% ≤ HbA1c < 6.5%	1772	17.37
5	6.5% ≤ HbA1c < 7.0%	734	7.20

Figure 2. Diabetes diagnosis at the end of follow-up, by HbA1c sub-group. For each HbA1c subgroup, the percentage of patients who were diagnosed with diabetes appears in dark colour, and the percentage not diagnosed in light colour. The six sub-groups were determined according to the first HbA1c value measured on the index day, as follows: Reference group: HbA1c < 4.5%; sub-group #1: 4.5% ≤ HbA1c < 5%; sub-group #2: 5% ≤ HbA1c < 5.5%; sub-group #3: 5.5% ≤ HbA1c < 6%; sub-group #4: 6% ≤ HbA1c < 6.5%; sub-group #5: 6.5% ≤ HbA1c < 7%.

Figure 3. Kaplan–Meier curve of the time to type 2 diabetes diagnosis, according to HbA1c sub-group on index day. The curves depict, for each HbA1c subgroup, the decreases in percentage of individuals who remained without a diagnosis of diabetes during the follow-up period, up to eight years.

Table 3. Cox regression analysis of the hazard ratio of HbA1c category for the development of type 2 diabetes (n = 10 201).

	Hazard ratio	95% CI	P-value
HbA1c sub-groups^a
1	1.03	0.58–1.81	0.93
2	1.39	0.81–2.36	0.23
3	2.19	1.29–3.71	< 0.01
4	4.82	2.83–8.20	< 0.01
5	7.57	4.43–12.93	< 0.01
Gender (male versus female)	1.14	1.05–1.25	< 0.01
Baseline cardiovascular diseases (present versus absent)	1.16	1.04–1.28	0.01
BMI > 25 kg/m^2	2.06	1.80–2.35	< 0.01
Age^b	1.00	1.00–1.01	0.10
Low socio-economic status	1.11	1.00–1.22	0.05

95% CI, 95% confidence interval.

^aThe hazard ratios of sub-groups 1–5 are in comparison to the reference group (HbA1c < 4.5%).

^bAge per year.