Diagnostic test accuracy of outpatient blood pressure measurement to detect hypertension in older people

Introduction

Older people presenting to outpatient (OP) clinics require blood pressure (BP) measurement to consider morbidity contributing to falls and long-term cardiovascular risk. However, BP measurements taken in the outpatient setting (OBPs) may not correlate with BP patterns obtained using ambulatory measurements (ABPMs). ABPM is considered a more accurate method of diagnosing hypertension than OBP in the general population. Using OBPs for clinical decision-making in isolation risks either under or over-diagnosis of hypertension. This study aimed to investigate the diagnostic test accuracy of OBP to detect hypertension in a cohort of older people.

Method

We retrospectively evaluated consecutive attendances of older people to a multidisciplinary outpatient clinic over a period of four months. We obtained demographic and clinical data from electronic records and compared individual OBPs with subsequent ABPMs. We defined hypertension using NICE criteria and followed the “Standards for Reporting of Diagnostic Accuracy” (STARD) to categorise data.

Results

Among 208 consecutive OP attendances, we identified 194 patients with OBPs, of whom 65 subsequently underwent ambulatory blood pressure monitoring (ABPM). The mean age of attendees was 76 years, 65% were female, and 49% had a history of hypertension. 121(62%) patients were hypertensive on OBP – of the 35 who progressed to ABPM, only 14 were hypertensive (a positive predictive value (PPV) of 40%). Seventeen patients without hypertension on OBP had ABPM, of whom three were hypertensive on ABPM (negative predictive value (NPV) of 82%).

Conclusion

Older people who are normotensive on OBP are likely also to be normotensive on ABPM. However, the majority who appear to be hypertensive on OBP are not found to be hypertensive on ABPM. We conclude that OBP has low diagnostic accuracy in this population, risking significant overdiagnosis of hypertension. Obtaining ABPM for older people with hypertension on OBP is likely to aid clinical decision-making.