Medical metrology

Modern healthcare relies to an ever increasing extent on quantitative measurements. Many of these measurements are made on blood and tissue samples in externally accredited medical testing laboratories where great care is exercised to control the quality of the measurements. However, a rapidly increasing number of (mostly physical) measurements are made in clinicians’ offices, patients’ homes, nursing homes, hospital wards, intensive care units and operating theatres where quality control is sometimes less than thorough or even non-existent. Diagnosis, treatment and follow up often depend strongly on these physical measurements, and it is important that the quality control is adequate and fit for purpose.

It is well known that medical errors are a major cause of morbidity and mortality, in both ambulatory (outpatient) settings and in hospitals. Measurement error, however, is very seldom considered as a possible factor contributing to medical errors. Metrologists know that when measurement systems are not properly maintained and calibrated, sooner or later the measurements become misleading.

We find it difficult to understand why a society that is prepared to pay good money to ensure that devices such as supermarket scales and fuel dispensers are regularly inspected and traceably calibrated is reluctant to require similar quality control of medical devices such as sphygmomanometers  (blood pressure monitors), spirometers (lung function testing devices) and tonometers (eye pressure measuring devices).

Links to selected studies we have published on metrological and related issues in medicine are provided below. A major objective of these studies is to demonstrate the sensitivity of medical decisions to errors in physical measurements, and hence provide evidence to motivate for good quality control.

Please contact us to request reprints of any of these articles.

Effects of systematic errors in blood pressure measurements on the diagnosis of hypertension
An mathematical study showing that if a clinician wishes to limit over- and under-detection of systolic hypertension to less than 20%, her sphygmomanometer should not systematically over- or under-read by more than 3 mm Hg. 

Lack of sphygmomanometer calibration causes over- and under-detection of hypertension – a computer simulation study.
A Monte Carlo simulation of the measurement of the blood pressure of all Australian adults using calibrated and uncalibrated sphygmomanometers, showing substantial over-and under-detection of hypertension when
sphygmomanometers are uncalibrated. Random variations in blood pressure were included in the simulations.

Sphygmomanometer calibration – why, how and how often?
A review of sphygmomanometer errors and recommendations regarding in-service maintenance and calibration of sphygmomanometers. Co-authored by a senior metrologist from the National Measurement Institute and a clinician from the Royal Australian College of General Practitioners.

Lax sphygmomanometer standard causes over- and under-detection of hypertension – a computer simulation study.
A Monte Carlo simulation of the measurement of the blood pressure of all Australian adults using sphygmomanometers that comply with present standards, and sphygmomanometers with systematic errors limited to ±1 mm Hg. Results show that systematic sphygmomanometer errors
permitted by the current standard are a preventable cause of clinically significant over- and under-detection of hypertension.

Can we trust automatic sphygmomanometer validations?
A review suggesting that automatic sphygmomanometers, now commonly used to detect, treat and monitor hypertension, should be validated in facilities accredited to ISO 17025 or a similar standard. At present, automatic sphygmomanometers can be validated by anyone against uncalibrated reference sphygmomanometers. 

Potential effects of systematic errors in intraocular pressure measurements on screening for ocular hypertension
A mathematical study showing that systematic errors in measurements of intraocular pressure of ±1 mm Hg may cause an apparent increase in the prevalence of ocular hypertension of 58%, or 34% of individuals with ocular hypertension to be missed. Tonometers should be maintained and calibrated to control systematic errors in IOP to substantially less than ±1 mm Hg.

Review of medical metrology: Lack of quality control of physical medical measurements
A review of metrological quality control of a range of physical medical measurements, concluding that there is a clear, unmet need to lift the quality of physical medical measurements to the standards that pertain in science, industry and trade.