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Accuracy Criteria Device Validation Protocols

Accuracy Criteria

Importance of Validation

There is a large market for blood pressure measuring devices, not only in clinical medicine, but also with the public where the demand for self-measurement of blood pressure is growing rapidly. For the consumer, whether medical or lay, device accuracy should be of prime importance in selecting a blood pressure measuring device. However, the majority of devices available have not been evaluated independently for accuracy according to the three most widely used protocols the British Hypertension Society (BHS) Protocol and the Association for the Advancement of Medical Instrumentation (AAMI) Standard, and more recently the International Protocol of the European Society of Hypertension (IP).

The purpose of the dabl®Educational Trust website is to produce regular reviews of blood pressure measuring devices to guide the would-be-purchaser through a complex market. As the majority of blood pressure measuring devices has not been independently validated, the devices listed on the website are representative, therefore, of only a fraction of the many devices available. It is hoped that manufacturers will wish to list devices for which validation is planned and that in time the devices listed will be representative of the market.

Declaration of Blood Pressure Measuring Device Equivalence

If a manufacturer has two or more devices covered by the same validation study a Declaration of Blood Pressure Measuring Device Equivalence must be completed by a Director of the manufacturing company. This signed and sealed document will be listed as a reference in the validation tables. Click here for a copy.

Criteria for device recommendation

The following criteria have been used to designate devices according to accuracy:

'Recommended' - a device that achieves a BHS grade B or A for both systolic and diastolic blood pressures, and/or passes the ESH International Protocol criteria for both systolic and diastolic pressures.

'Not recommended' - devices that cannot be recommended fall into two categories: firstly, there are devices which clearly fail to achieve the above accuracy criteria and are categorically not recommended for clinical use when accurate measurement is required, and secondly, there are devices for which the evidence needed to make a recommendation is uncertain or unsatisfactory, and such devices are designated as 'questionable'. Devices in this category cannot, however, be recommended for clinical use when accurate measurement is required on the basis of the evidence available, though this designation might later change if further evidence allowed for the removal of the 'questionable' designation. These categories are listed in the tables as:

  • Not recommended - on evidence - a device that achieves a BHS grade C or D for either systolic or diastolic pressure, and/or fails the ESH International Protocol criteria for either systolic or diastolic pressures.

  • Not recommended - questionable evidence - a device for which there is doubt about the strength of evidence, as may occur in the following circumstances: (i) when the validation results are presented in abstract form only without sufficient detail being available to appraise the methodology, it may be best to withhold an opinion until the full results have been published, or at least provided to a would-be purchaser by the manufacturer; (ii) when the conditions of the protocols have not been fully adhered to (listed as 'protocol violation'); (iii) when a device fulfils the criteria of the AAMI protocol alone for both systolic and diastolic pressures; (iv) when a device fulfils the AAMI criteria for intra-arterial validation, it may be best to await a validation against indirect blood pressure measurement before recommending the device for general clinical use (the BHS and ESH International Protocol do not advocate validation using direct intra-arterial measurement).

Approval by CE, ISO or any other body are not criteria considered for device recommendation.

Protocol Adherence

Adherence to protocols is critical. The criteria within modern protocols are derived from a wealth of data and have been rigorously tested. Deviations from this weaken the validity of the results. In particular, recruitment of extra subjects tends to be common. This is usually due to extra subjects being tested while striving to attain quotas for the highest and lowest ranges. However, their inclusion affects the blood pressure distribution upon which the outcome criteria are based. The correct approach is to use only the exact numbers suggested in the order they are recruited. Independence of the validation is paramount and any assistance by the manufacturers in the validation procedure automatically compromises the results.

There is no valid reason for protocol deviation and, scientifically, little tolerance can be made for this. The tables list the outcomes as stated in the papers (a pass means a pass for both SBP and DBP ) and is followed by columns leading to whether or not the device can be recommended for blood pressure measurement. Quite simply, if a device passes a correclty performed published validation, that assesses individual measurements, then it is recommended.

Accuracy criteria tables

The following tables summarise the accuracy criteria for the International Protocol of the European Society for Hypertension (IP), the British Hypertension Society (BHS) Revised Protocol of 1993 and their original protocol of 1990, and the Association for the Advancement of Medical Instrumentation (AAMI) Standard.

These tables are for quick reference purposes only and should not be used without knowledge of the full protocols.

ESH International Protocol 2010
Sequential Measurements
IP Grading Part 1 - Minimum Requirements
N ≤ 5 mmHg ≤ 10 mmHg ≤ 15 mmHg
Two of 73 87 96
All of 65 81 93
IP Grading Part 2
N 2/3 ≤ 5 mmHg   0/3 ≤ 5 mmHg
At least 24    
At most     3
Recruitment Ranges
SBP DBP
mmHg Subjects mmHg Subjects
90*..129 10 - 12 40*..79 10 - 12
130..160 10 - 12 80..100 10 - 12
161..180* 10 - 12 101..130* 10 - 12
* Altogether, up to 4 recruitment pressures are permitted to be outside these limits.
Test Measurement Distribution
SBP DBP
mmHg Measurements mmHg Measurements
≤ 100 ≥ 1 ≤ 50 ≥ 1
< 130 22 - 44* < 80 22 - 44*
130..160 22 - 44* 80..100 22 - 44*
> 160 22 - 44* > 100 22 - 44*
≥ 170 ≥ 1 ≥ 120 ≥ 1
* The difference between the maximum and minimum of these 3 counts for SBP and, separately, for DBP, must be less than or equal to 19.

ESH International Protocol 2002
Sequential Measurements
IP Grading Phase 1 - Minimum Requirements
N ≤ 5 mmHg ≤ 10 mmHg ≤ 15 mmHg
At least one of 25 35 40
IP Grading Phase 2.1 - Minimum Requirements
N ≤ 5 mmHg ≤ 10 mmHg ≤ 15 mmHg
Two of 65 80 95
All of 60 75 90
IP Grading Phase 2.2
N 2/3 ≤ 5 mmHg   0/3 ≤ 5 mmHg
At least 22    
At most     3
Ranges
SBP DBP
mmHg Subjects Phase 1,2 mmHg Subjects Phase 1,2
90..129 5, 11 40..79 5, 11
130..160 5, 11 80..100 5, 11
161..180 5, 11 101..130 5, 11

BHS Revised Protocol (1993)
Sequential Measurements
Grading - Minimum Requirements
Grade ≤ 5 mmHg ≤ 10 mmHg ≤ 15 mmHg
A 60 85 95
B 50 75 90
C 40 65 85
D 0 0 0
Ranges
SBP DBP
mmHg Minumum mmHg Minumum
< 90 8 < 60 8
90..129 20 60..79 20
130..160 20 80..100 20
161..180 20 101..110 20
> 180 8 > 110 8

BHS Protocol (Original 1990)
Simultaneous or Bracketed Sequential Measurements
Grading - Minimum Requirements
Grade ≤ 5 mmHg ≤ 10 mmHg ≤ 15 mmHg
A 80 90 95
B 65 85 95
C 45 75 90
D 0 0 0
Ranges
SBP DBP
mmHg Minumum mmHg Minumum
100..140 15% of BPs 60..80 20% of BPs
140..180 15% of BPs 80..100 20% of BPs
180..220 15% of BPs 100..120 20% of BPs
220..240 15% of BPs    

AAMI Protocol
Simultaneous Measurements
Criterion 1 Grading (at least 255 pairs of individual measurements)
Grade Mean   SD
Pass ≤ 5mmHg and ≤ 8mmHg
Fail > 5mmHg or > 8mmHg
Criterion 1 Grading (85 subject mean pressures)
(Linear interpolation of SD limits or Means between those listed)
Grade Mean (mmHg)   SD (mmHg)
Pass 5 and ≤ 4.81
or 4.5 and ≤ 5.24
or 4 and ≤ 5.64
or 3.5 and ≤ 5.97
or 3 and ≤ 6.25
or 2.5 and ≤ 6.47
or 2 and ≤ 6.65
or 1.5 and ≤ 6.78
or 1 and ≤ 6.87
or 0.5 and ≤ 6.93
or 0 and ≤ 6.97
Fail > 5 or > limit
Ranges
SBP DBP
mmHg Requirement mmHg Requirement
≤ 100 ≥ 5% ≤ 60 ≥ 5%
≥ 140 ≥ 20% ≥ 85 ≥ 20%
≥ 160 ≥ 5% ≥ 100 ≥ 5%

 

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