Undiagnosed diabetes based on HbA1c by socioeconomic status and healthcare consumption in the Tromsø Study 1994-2016

Abstract

Introduction: We aimed to investigate whether the proportion of undiagnosed diabetes varies by socioeconomic status and healthcare consumption, in a Norwegian population screened with glycated hemoglobin (HbA_1c).

Research design and methods: In this cohort study, we studied age-standardized diabetes prevalence using data from men and women aged 40-89 years participating in four surveys of the Tromsø Study with available data on HbA_1c and self-reported diabetes: 1994-1995 (n=6720), 2001 (n=5831), 2007-2008 (n=11 987), and 2015-2016 (n=20 170). We defined undiagnosed diabetes as HbA_1c ≥6.5% (48 mmol/mol) and no self-reported diabetes. We studied the association of education, income and contact with a general practitioner on undiagnosed diabetes and estimated adjusted prevalence ratio (aPR) from multivariable adjusted (age, sex, body mass index) log-binomial regression.

Results: Higher education was associated with lower prevalence of diagnosed and undiagnosed diabetes. Those with secondary and tertiary education had lower prevalence of undiagnosed diabetes (aPR for tertiary vs primary: 0.54, 95% CI: 0.44 to 0.66). Undiagnosed as a proportion of all diabetes was also significantly lower in those with tertiary education (aPR:0.78, 95% CI: 0.65 to 0.93). Household income was also negatively associated with prevalence of undiagnosed diabetes. Across the surveys, approximately 80% of those with undiagnosed diabetes had been in contact with a general practitioner the last year, similar to those without diabetes.

Conclusions: Undiagnosed diabetes was lower among participants with higher education. The hypothesis that those with undiagnosed diabetes had been less in contact with a general practitioner was not supported.

Keywords: diagnosis; education; epidemiology.

Figure 1

Age-standardized diabetes prevalence by educational level in Tromsø 4 (1994–1995), Tromsø 5 (2001), Tromsø 6 (2007–2008) and Tromsø 7 (2015–2016). In white, percentage of known diabetes and in gray percentage of undiagnosed diabetes; defined as HbA_1c measurement ≥6.5% (48 mmol/mol) and no self-reported diabetes. The percentage value on the top of the bars represents the proportion of undiagnosed diabetes to all diabetes. HbA_1c, glycated hemoglobin.

Figure 2

Percentage of participants who visited a general practitioner during the last 12 months prior to screening visit among participants with undiagnosed diabetes and no diabetes. Tromsø 4 (1994–1995), Tromsø 5 (2001), Tromsø 6 (2007–2008) and Tromsø 7 (2015–2016). In white, percentage of participants without diabetes and in gray percentage of undiagnosed diabetes, defined by an HbA_1c measurement ≥6.5% (48 mmol/mol) and not self-reported diabetes. After adjustment for sex, age, BMI and education, the OR for general practitioner contacts in those with undiagnosed diabetes compared with those without diabetes was 1.18 (p=0.64) in Tromsø 4. In Tromsø 5, the OR was 0.84 (p=0.45), in Tromsø 6 the OR was 1.09 (p=0.67) and in Tromsø 7 the OR was 0.80 (p=0.17). Results stratified by sex, age, education, income, and BMI are shown in the online supplemental table 3. BMI, body mass index; HbA_1c, glycated hemoglobin.