Gender-specific clinical risk scores incorporating blood pressure variability for predicting incident dementia

Dear Editor,

We thank Dr. Ser for her detailed reading of our study,¹ and starting this important dialogue on the importance of dementia in our aging global population. We fully recognize her point that the use of ICD-9 coding for determining a diagnosis of dementia will lead to an underdiagnosis. Indeed, the cited studies from Canada and Australia illustrate the problem of undercoding specifically on dementia. It is fair to assume that there would be a similar issue for the local data from China. We were not able to identify studies investigating the reliability of coding specifically for dementia in our locality. Nevertheless, based on a local study that calculated the trends of prevalence of dementia in the Hong Kong city based on census data,² an estimated 100 000 people above the age of 60 suffers from dementia in 2009 and it is projected to increase to approximately 330 000 patients in 2039, which is around 4.7% of the Hong Kong population similar to the incidence rate of 4.74% calculated in our study.

A meta-analysis of 76 studies involving individuals above the age of 60 in China between 1998 and 2012 also reported a disease prevalence of 8.4 million people, which amounts to around 4.6% of the total population.³ An updated estimate in 2018 reported that the diseased population increased up to 9.5 million people, which accounts for 5.3% of the total population.⁴ Thus, given the increasing prevalence of dementia under the population growth and aging, there is indeed a risk of underdiagnosis.⁵ Nevertheless, the coding diagnosis from our healthcare system covers not only accident and emergency and inpatient admissions but also ambulatory and outpatient clinic attendances. This is due to the fact that the public sector serves 80–90% of the local city with territory-wide linkage across various healthcare settings. Indeed, we fully acknowledge that dementia is significantly undercoded across healthcare systems worldwide. It would thus be of paramount importance to examine the prevalence of diagnosis in large cohorts of community-dwelling individuals to complement research studies based on administrative data.