CCDSS:  Report from the Canadian Chronic Disease Surveillance System: Hypertension in Canada, 2010

Canadian Chronic Disease Surveillance System (CCDSS)

The Canadian Chronic Disease Surveillance System (CCDSS) is a collaborative network of provincial and territorial surveillance systems, supported by the Public Health Agency of Canada (PHAC). In each province and territory, the health insurance registry database is linked to the physician billing and hospitalization databases. Started with diabetes surveillance and formerly known as the National Diabetes Surveillance System (NDSS), the CCDSS is currently expanding to include other chronic disease conditions. The CCDSS regularly seeks advice from Aboriginal groups, non-governmental organizations, and researchers in order to enhance and interpret the information from the system.

In 2009, PHAC expanded the CCDSS to track information on the prevalence and incidence of diagnosed hypertension in the Canadian population. Persons were considered cases of diagnosed hypertension if they met the following case criteria: two or more physician claims within two years, or one inpatient hospital separation abstract listing hypertension as a diagnosis with the International Classification of Diseases (ICD) 9^th Edition hypertension codes (ICD-9 or ICD-9-CM: 401-405) or equivalent 10^th Edition hypertension codes (ICD-10-CA: I10-I13 and I15). An expert group recommended the CCDSS case criteria based on recent validation studies conducted in Canada.^{Footnote 10 Footnote 11 Footnote 12 Footnote 13} The CCDSS case criteria exclude women with pregnancy induced hypertension to avoid including cases of hypertension that may resolve after delivery. In addition, the case criteria do not include individuals diagnosed with pulmonary hypertension (ICD-9 or ICD-9-CM code 416 or ICD-10-CA code I27). Full-time members of the Canadian Forces and individuals in the Royal Canadian Mounted Police and federal correctional facilities were not included as they are covered by federal jurisdiction as opposed to the publicly funded health registry administered by the provinces and territories.

Using administrative data for surveillance, as in the CCDSS, generally results in some misclassification of hypertension cases and non-cases. Therefore, the method of determining diagnosed hypertension requires a balance between the possibilities of not identifying people who have been diagnosed with hypertension (false-negatives) and identifying people who do not have hypertension (false-positives). A number of validation studies have indicated that the CCDSS case criteria minimize both false-negatives and false-positives and depict a relatively accurate picture of diagnosed hypertension in Canada.^{Footnote 10 Footnote 11 Footnote 12 Footnote 13}

The CCDSS does not identify individuals who have hypertension but have not yet been diagnosed with the condition by a physician. Results based on blood pressure measurements from the Canadian Heart Health Surveys in 1986-1992 showed that 42% of the study participants were unaware of their hypertension (47% of men and 35% of women).^{Footnote 14} Likely as the result of intensive efforts to improve the detection and management of hypertension, this has changed. In the 2006 Ontario Survey on the Prevalence and Control of Hypertension a much lower proportion of individuals with hypertension (13.7%) were unaware of their condition.^{Footnote 15} Similarly, national estimates from Cycle 1 of the Canadian Health Measures Survey conducted between 2007 and 2009 indicated that 17% of Canadians with hypertension were unaware.^{Footnote 16} Thus, trends presented in this report might underestimate the true prevalence of hypertension in Canada.

This report features the most recent data available, fiscal year 2006/07, as well as trend data from 1998/99 onwards. Where data on both diagnosed hypertension and diabetes are presented, trend data from 2000/01 onwards are presented as data for diabetes were not available prior to this year. Data for Nunavut and Québec were unavailable for this report but will likely be available in future reports. However, as noted in the applicable data tables and figures, the number of cases for Québec was estimated by applying the Canadian age-specific rates of diagnosed hypertension weighted to the Québec population. The CCDSS case criteria have not been validated for adults younger than 20 years of age; therefore the data presented in this report are only for adults aged 20 years and older.