How many BP readings is needed to ensure accurate assessment?

A recent study asserts that two blood pressure (BP) readings are enough unless the difference between the two readings is at least 10 mm Hg for both systolic (SBP) and diastolic BP (DBP).

“Guidelines differed on the required number of BP readings for accurate BP assessment,” the researchers said. “We, therefore, compared the mean of the first two BP readings with the overall mean of three readings in the diagnosis of hypertension.”

A validated automated electronic BP monitor was used to measure BP three times consecutively with a 1-min interval in volunteers aged ≥18 years. The researchers then compared the mean of the first and second BP readings with the mean of the three BP readings for the diagnostic accuracy of hypertension.

Of the 77,520 participants recruited, 65.2 percent and 25.2 percent had an SBP or DBP difference of at least 5 and 10 mm Hg between the first and second BP readings, respectively.

There were significant SBP/DBP differences (p<0.0001) noted between the mean of the first two BP readings and the overall mean of three readings, with an absolute value up to 1.28/1.11 mm Hg, irrespective of whether such difference between the first two BP readings was at least 5 or 10 mm Hg for SBP and DBP alone or both.

The mean of the first two BP readings showed good reliability and sufficient agreement in the diagnosis of hypertension, with a kappa statistic of at least 0.88. However, the difference between the first and second readings was ≥10 mm Hg for both SBP and DBP (κ=0.79). Notably, the diagnostic accuracy was similar across age quartile, sex, and BP category.