Validation of self diagnosis of high blood pressure in a sample of the Spanish EPIC cohort: overall agreement and predictive values. EPIC Group of Spain.

STUDY
OBJECTIVE: High blood pressure is a variable related to several chronic conditions whose repeated measurement in large cohort studies is often not feasible having to rely on the self reporting of the subjects. The aim of the study is to validate such self diagnosis in a sample of members from the Spanish EPIC cohort study.
DESIGN: Comparison of high blood pressure self diagnosis with the information provided by the personal medical record drawn from the primary health centre of reference for such population.
SETTING: A small town near the EPIC-Murcia centre, one of five Spanish EPIC centres located in the south east, where inclusion in the cohort was offered to the general population. PARTICIPANTS: The agreement between self reported high blood pressure status and data from medical records was measured in a representative sample of men and women (n = 248) aged 30-69 years. Medical records were studied for a diagnosis of high blood pressure, an anti-hypertensive pharmacological treatment or subject's inclusion in a hypertension control programme run in the medical centre only for hypertensive people (definite high blood pressure cases). As well, in the absence of such a diagnosis, medical annotations of systolic or diastolic high blood pressure > or = 140/90 mm Hg (possible high blood pressure cases) were considered. Sensitivity, specificity, positive and negative predictive values and kappa scores were calculated for all, definite and possible high blood pressure cases. Variables associated with the probability of having a true positive or negative self report of high blood pressure were also tested. MAIN
RESULTS: As expected, sensitivity was higher among definite cases (72.7%) than among possible cases (31.6%). Accordingly, the agreement between self report and medical record was higher for definite cases (kappa = 0.65) than for possible (kappa = 0.29 cases leading to a moderate overall agreement for all cases (kappa = 0.58; 95% CI: 0.47, 0.69). Having some level of education (OR: 0.31; 95% CI: 0.09, 1.05) was negatively associated to a true self report of high blood pressure while being female was positively associated (OR: 4.01; 95% CI 1.04, 16.8). No variable showed any association with having a true self report of being normotensive.
CONCLUSIONS: High blood pressure self report shows a moderate agreement with medical information in this cohort allowing it to be used, with caution, as a surrogate variable of actual blood pressure status. However, because of its moderate sensitivity, it is not possible to rule out some underestimation when using self reported high blood pressure information for high blood pressure frequency measurements such as prevalence or incidence rates. This underestimation will be higher among men and educated people.