Studies of drug-treated diabetes in the county of Jämtland, Sweden, based on prescription of insulin and oral antidiabetic drugs

The influence of non-response in a population-based cohort study on type 2 diabetes evaluated by the Swedish Prescribed Drug Register

Bias due to non-response in observational studies may lead to false risk estimates. We evaluated potential selective non-response in Stockholm Diabetes Prevention Program (SDPP) using a population-based drug register. A cohort of 12,952 men and 19,416 women, aged 35-56 years, was screened for diabetes and family history of diabetes (FHD). Response rate: 79% in men and 85% in women. Of the 4,209 men and 6,916 women that were invited, 70 and 68% participated in a baseline health examination including oral glucose tolerance test. A follow-up was performed in 79% of male and 70% of female baseline participants. We used data from the prescription register to estimate absolute risks and ORs for drug-treated diabetes in the non-response/non-participation groups. At both screening and baseline steps absolute risks of drug-treated diabetes were equal in non-participants and participants. Adjusted ORs were 0.9-1.0. At follow-up, absolute risks were higher among non-participants than participants, men 6.2/4.4% and women 2.6/1.6%, adjusted ORs 1.4 (0.9-2.3) and 1.5 (0.9-2.4), suggesting selective non-participation. Further analyses of FHD, smoking, physical activity, socioeconomic position and psychological distress demonstrated no previous false risk estimates for type 2 diabetes. However, for body mass index, there were indications of overestimation in women. We conclude that bias from non-response was not present at screening or baseline steps, suggesting that diabetes prevalence and risks may be estimated from a population-based cohort study with high attendance rate such as the SDPP. However, follow-up data should be treated with some caution, since the sample may have become biased.

Is questionnaire information valid in the study of a chronic disease such as diabetes? The Nord-Trøndelag diabetes study

STUDY OBJECTIVE

The aim was to validate information about diabetes mellitus collected by questionnaire in a large epidemiological survey.

DESIGN

Questions on diabetes diagnosis, medical treatment for diabetes, diabetes duration, and hypertension treatment were selected from the Nord-Trøndelag health survey questionnaires. One of the municipalities was selected for the validation study.

SETTING

The health survey 1984-86 addressed all inhabitants > or = 20 years of age in Nord-Trøndelag county, Norway; 76,885 (90.3%) of the eligible population participated in answering the question on diabetes.

PARTICIPANTS

All inhabitants in the municipality answering "yes" to the question on diabetes (n = 169) and the persons with the same sex born closest before and after each diabetic patient and answering "no" to the diabetes question (n = 338) were included.

MEASUREMENTS AND MAIN RESULTS

A very thorough search was made in the medical files of the general practitioners in the municipality for corresponding information. Compared to the files, diabetes was verified in 163 out of the 169. The commonest cause of discrepancy was renal glycosuria. One out of the 338 registered non-diabetic persons was found to have diabetes. Diabetic patients tended to overestimate diabetes duration significantly. Insulin treatment was verified in 19/20 (95%) and treatment with oral hypoglycaemic agents in all 44 with an affirmative questionnaire answer. A negative answer on insulin and oral hypoglycaemic agents was verified in 100% and 99% respectively.

CONCLUSIONS

The concordance was considerably higher than in a comparable Norwegian study performed 10 years earlier. Patient administered questionnaires may be a very reliable source of information for epidemiological purposes in a well defined chronic disease such as diabetes mellitus.

Diabetes mellitus in north Sweden: prevalence assessed from prescriptions for anti-diabetic agents

A prescription inventory was performed over a period of 3 months in all pharmacies in Sweden's northernmost province. Norrbotten, in order to assess the prevalence of diabetes treated with insulin and oral anti-diabetic agents. A total of 4869 prescriptions were collected from 3482 individuals, of whom 1746 (50.1%) were men. The prevalence of drug-treated diabetes was thus 13.27/1000 inhabitants (95% confidence interval (CI) 12.8-13.7) in the province. Nearly half (47.9%) of all drug-treated diabetics were treated with insulin and the majority (74%) were over 55 years of age, with only 449 (13%) being less than 40 years old. The prevalence of diabetes was highest in individuals aged 75-84 years; in this age group it was 55.47/1000 (95% CI 50.9-58.7). There was considerable regional variation in the prevalence of diabetes in Norrbotten, with a mean prevalence of 23.84/1000 (95% CI 22.1-25.6) in the municipalities in the Torneå Valley, compared to 13.08/1000 (95% CI 1.19-1.28) for the remainder of Norrbotten. While there was no difference in the prevalence of drug-treated diabetes between men and women in the province as a whole, a slightly higher prevalence was found in women (27.41 vs. 24.73/1000) in the Torneå Valley. The prevalence of diabetes mellitus in individuals over 40 years of age was 36.62/1000 (95% CI 3.73-4.36) in The Torneå Valley, 24.38/1000 (95% CI 22.8-24.7) in the remainder of Norrbotten, and 27.88/1000 (95% CI 2.50-2.68) in the province as a whole. The estimated prevalence of diabetes mellitus in Norrbotten, including patients treated by diet alone, was of the order of 20.21/1000, with a prevalence of 40.00/1000 in subjects over the age of 40 years. Thus the prevalence of diabetes appears to be higher in the Torneå Valley than in the rest of Norrbotten, while it is apparently lower than has been reported in North Finland.