Testing the accuracy of blood pressure measuring devices: challenges and pitfalls of validation studies

Several protocols have been devised for the validation of blood pressure (BP) measurement monitors to establish minimum standards of accuracy. Three aspects are crucial for improving the agreement between the device and the reference BP which depend on the quality of the laboratory and the experience of the investigators: (a) the choice of the most appropriate cuff in relation to the subject's arm size. As shown by Marks and Groch the measurement error gradually and remarkably increases in a linear fashion when the optimal cuff width/arm circumference ratio is not achieved. This mandates that in expert laboratories numerous cuffs should be available with progressively increasing bladder width. (b) Minimizing patient's BP variability during testing is the most challenging goal to achieve for reducing the SD of the between-method BP differences. Habituation to the medical environment can be increased by prolonging the pretest interval to 15-30 min. (c) The laboratory must be of high standard both in terms of environmental conditions and available instrumentation. A perfect harmony and interrelationship of the team members in the various stages of the test must be achieved. This condition is acquired through a long period of formal education and supervised practice. Recently, several validation studies have achieved bias and precision far below the minimum required criteria probably due to a more careful and rigorous assessment of performance. This led some authors to suggest to move the threshold of the mean difference between device and reference BP from 5 down to 3 mmHg.