The extent and implications of sphygmomanometer calibration error in primary care

Aim: The sphygmomanometer is an essential piece of diagnostic equipment, used in many routine consultations in primary care. Its accuracy depends on correct maintenance and calibration. This study was designed to: (1) assess the maintenance and calibration of sphygmomanometers in use in primary care; (2) assess the clinical, ethical, legal and public health implications of our findings. Method: A researcher assessed the accuracy of mercury and aneroid sphygmomanometers in use in 231 English general practices. He also made enquires about arrangements for the maintenance and calibration of sphygmomanometers. We conducted a small telephone survey in general practices across the country to determine maintenance and calibration arrangements across the country. We carried out a modelling exercise to explore the clinical, ethical and public health implications of our findings. Results: Of 1462 sphygmomanometers, 9.2% gave readings were more than 5 mm Hg inaccurate. No practice had arrangements for maintenance and calibration of sphygmomanometers. Nationally, one of 54 practices had an arrangement for maintenance and calibration. True hypertension is very uncommon in women under 35, a blood pressure which is measured as high is much more likely to be caused by calibration error than by hypertension. Conclusion: It is rare for sphygmomanometers used in primary care to be maintained and calibrated. Because of this women under 35 are at risk of misclassification and inappropriate treatment. This has ethical and public health implications. Clinicians using equipment which has not been maintained and calibrated may be medically negligent.