How accurate are blood pressure monitors?

Do blood pressure monitors measure accurately?

Anyone looking to purchase a blood pressure monitor will be overwhelmed by the selection. There are countless manufacturers, and many offer several devices. There are some cheap bargains starting at around 10 euros, but you can also spend three-digit amounts.

Of course, this raises the question of whether such a cheap device measures just as well as an expensive one. To make it short: You can't say that directly. Unfortunately, we need to elaborate a bit.

Approval as a medical device

Measuring devices are medical products, and there is a specific approval process for them. This involves regulations, standards, and laws. The measurement accuracy is also tested for this approval.

Technical testing

This is done through technical testing, where, for example, the pressure manometer and the cuff are checked. However, this says little about the measurement accuracy on humans.

Clinical validation

Therefore, a measuring device requires clinical validation. Simply put, a certain number of people are taken, and their blood pressure is measured. This is compared with a measurement according to Korotkoff, that is, with a stethoscope. A testing protocol specifies how closely the values must match for the device to still be approved. The number of patients and which ones are used for the testing are also specified there.

Testing protocols

There is not just one testing protocol. These can differ quite a bit. The more well-known protocols are those from ESH, BHS, AAMI, and DHL. However, manufacturers were not bound by these.
With the Medical Device Regulation - the new medical device law from 2017 - there is now a standard ISO 81060 (AAMI/ESH/ISO), which represents a mandatory protocol. However, many measuring devices on the market still have an old approval.

Comparison table of validation protocols:

	ESH	BHS	AAMI	DHL	AAMI/ESH/ISO
Number of Participants	33	85	>=85	96	>=85
Age	>=25	15-80	>12	>20	>12
Blood Pressure Range (SBP = Systolic Blood Pressure, DBP = Diastolic Blood Pressure)	SBP (mmHg): <130: 10-12 Participants, 130-160: 10-12, >160 mmHg: 10-12 DBP (mmHg): <80: 10-12, 80-100: 10-12, >100: 10-12	SBP (mmHg): <90: ≥8 Participants, 90-129: ≥20, 130-160: ≥20, 161-180: ≥20, >180: ≥8, DBP (mmHg): <60: ≥8 Participants, 60-79: ≥20, 80-100: ≥20, 101-110: ≥20, >110: ≥8	SBP (mmHg): ≤100 mmHg: ≥5% of Measurements, ≥140 mmHg: ≥20%, ≥160: ≥5%, DBP (mmHg): ≤60 mmHg: ≥5%, ≥85 mmHg: ≥20%, ≥100 mmHg: ≥5%	20-40 Years SBP (mmHg): ≤140: 12 Participants ≥141: 12 DBP (mmHg): ≤90: 12 ≥91: 12 41-70 Years: SBP: ≤120: 8 121-140: 16 141-160: 16 ≥161: 8 DBP: ≤80: 8 81-90: 16 91-100: 16 ≥101: 8 ≥71 Years: SBP: ≤140: 12 >141: 12 DBP: ≤90: 12 >91: 12	SBP (mmHg): ≤100 mmHg: ≥5% of Measurements ≥140 mmHg: ≥20%, ≥160: ≥5%, DBP (mmHg): ≤60 mmHg: ≥5%, ≥85 mmHg: ≥20%, ≥100 mmHg: ≥5%
Inclusion Criteria	Criteria based on the number of measurements with a difference between test and reference blood pressure of ≤ 5, 10, 15 mmHg Criteria for individual blood pressure measurements (Part 1) individual participants (Part 2) Part 1: Passed if 73.7% (73/99) of the differences between the measurements ≤ 5 mmHg, 87.9% (87/99) ≤ 10 mmHg, 97.6% (96/99) ≤ 15 mmHg Part 2 (Accuracy): Number of participants with 0, 2 or 3 absolute differences ≤ 5 mmHg	Classification system (A, B, C, D) based on differences between paired measurements of ≤ 5, 10, 15 mmHg separately for each observer and separately for SBP and DBP Additionally, mean differences ≤ 5 mmHg and standard deviation ≤ 8 mmHg (AAMI recommendations)	Criteria based on mean blood pressure differences and their standard deviation criteria for individual blood pressure measurements and individual persons. Criteria 1 and 2 should be applied for SBP and DBP Criterion 1 (for individual blood pressure measurements): The mean blood pressure difference is ≤ 5 mmHg and the standard deviation ≤ 8 mmHg Criterion 2 (for individual participants): The mean difference and the standard deviation of the blood pressure measurements are within the threshold defined by the mean of Criterion 1	Criteria based on mean difference and standard deviation and the point system for individual paired SBP and DBP measurements Passed if the device meets all the following criteria: Mean difference for SBP and DBP ≤ 5 mmHg and the standard deviation ≤ 8 mmHg and score ≥ 55% of the maximum achievable score.	Criteria based on mean blood pressure differences (test vs. reference) and their standard deviation criteria for individual blood pressure measurements and individual participants. Criteria 1 and 2 should be applied for SBP and DBP Criterion 1 (for individual blood pressure measurements): The mean blood pressure difference is ≤ 5 mmHg and the standard deviation ≤ 8 mmHg. Criterion 2 (for individual participants): The mean difference and the standard deviation of the averaged blood pressure differences must be within a threshold defined by the mean of Criterion 1. Additionally, the number of absolute blood pressure differences within 5, 10, and 15 mmHg (ESH-IP2) and standardized Bland-Altman scatter plots are presented. The mean test-reference blood pressure difference and the standard deviation per cuff subgroup must be reported without pass/fail criteria for the test device

In addition, there are many other criteria, such as the selection of test subjects, how measurements are taken, etc. But even so, it is already clear that the tests are quite different.

Accuracy

So, you cannot say how accurate a device is. However, you can say that it has passed a validation - that is, a test. The more demanding the validation, the better it is, of course.
You can also view the testing protocols online in part.

Why clinically validate?

The doctor measures using the Korotkoff method

But why is this validation even necessary? This is because the measuring devices today work oscillometrically. In this case, the systolic and diastolic blood pressure is not actually measured, as is the case with the Korotkoff measurement using a stethoscope. The two values are then derived from the maximum vascular oscillation using algorithms. Especially in people with arrhythmia, increased arterial stiffness, diabetes, or tremors, there are problems here. To ensure that this derivation works well for as many people as possible, clinical validation is necessary.

What does this mean?

Measuring devices are tested for accuracy before they can be sold. However, one should not be under any illusions here. The range of what is still approved is already quite large.
There is also not one device that is perfectly suitable for everyone. You should choose one that shows the most reliable results in a test group that is similar to yourself (age, gender, arm circumference, heart rhythm disorders, arterial stiffness, etc.). And that is the tricky part, where it unfortunately becomes a science.

Since individual measurements can be inaccurate, one should not be unsettled by a single measurement value. More important and also significantly more accurate are regular measurements that allow you to keep an overview of all values. For this purpose, BloodPressureDB is suitable to see changes over time and to be able to act sensibly.

Download the app now and benefit from the clear presentation.

By Horst Klier. This article is medically reviewed. Last updated by Sabine Croci (12/2023).
Information on the website and within the app cannot replace a consultation with a doctor, but can certainly complement it.

We hope you found the article on the topic helpful. Correct measurement is very important for good blood pressure management. Our app BloodPressureDB helps with that. Concrete explanations guide you through a guideline-compliant measurement. The app also reminds you if you wish. These features are also fully available in the free version. Get the free app now.

Our offering meets the afgis transparency criteria. The afgis logo stands for high-quality health information on the internet.