When calculating the difference between alternating auscultatory reference standard (ARS) and the automated device-under-test (DUT) blood pressure (BP) measurements, the European Society of Hypertension International Protocol (ESH-IP) allows investigators to choose the closest ARS value to the DUT value, rather than using the mean of the ARS readings [which is mandated by the International Organization for Standardization (ISO)]. The impact of this rule on ESH-IP validation study results is unknown and was assessed.
Design and methods
Nine alternating BP measurements performed according to the ISO protocol were obtained in 94 subjects. The impact of using the closest rather than the mean ARS reading on mean error, SD of the difference, and proportion of readings with DUT-ARS differences within 5, 10, and 15 mmHg was determined.
Mean age was 58.6 ± 18.3 years, screening BP was 126.4/77.7 mmHg, and arm circumference was 32.0 ± 4.7 cm. DUT-ARS difference was 0.0 ± 5.3/−0.5 ± 5.0 mmHg using the closest ARS and −0.2 ± 6.5/−0.7 ± 5.9 mmHg using the mean ARS. When using the closest rather than the mean ARS value, the proportion of systolic readings with absolute DUT-ARS differences ≤5 mmHg was 73% (vs. 60% for the mean ARS method), ≤10 mmHg was 93% (vs. 88%), and ≤15 mmHg was 99% (vs. 98%). Corresponding values for diastolic BP were 73% (vs. 62%) for differences ≤5 mmHg, 94% (vs. 91%) for ≤10 mmHg, and 99% (vs. 99%) for ≤15 mmHg.
Using the closest rather than the mean ARS value results in more favourable validation study results and increases likelihood of passing.