NHS risking patients’ lives with imperial scales

Six months after an official report warned of systemic negligence in medical weighing practice within the NHS, the Department of Health has failed to issue the necessary safety alert to hospital trusts to ensure that the report’s recommendations are implemented.

After a series of pilot studies in 2007 found some hospital staff using inaccurate or unsuitable scales to calculate dosages of medication for patients, including small children, LACORS (the Local Authorities Coordinators of Regulatory Services) set up the National Medical Weighing Project.

Interim Report – August 2008

Published in August 2008, the project’s interim report noted,

  • “Staff do not consider scales to be medical equipment”
  • “The amount of cheap bathroom scales in critical locations is astonishing”
  • “One of the most potentially harmful issues is that of switchable scales – those that can display metric, imperial and other units. The risk is that medication could be administered based on a readout that was assumed to be metric.”


LACORS made a series of recommendations to hospital trusts, which included:

  • All scales used for medical applications should be accuracy Class III or higher.
  • Any equipment that is found to be inaccurate should be immediately removed from service and either repaired or replaced.
  • All scales used for medical applications should only display metric units. There should be no capacity for switching or dual readouts. Trusts should be aware of the pitfalls of using switchable scales and may wish to consider replacing them.

The report pointed out that implementing its recommendations would lead to significant improvements in patient care, and the ability for hospital trusts to demonstrate due diligence in relevant clinical negligence claims.

Final Report – June 2009

Commenting on changes observed in hospitals that had been previously visited in 2008, the Final report of the LACORS National Medical Weighing Project 2008/9, published in June 2009, reiterated the earlier report’s findings:

“The area with the most room for improvement (and potential to cause harm) is scales capable of showing metric and imperial units. While numbers have decreased, nearly one third of all scales in use are switchable. A staggering one in ten of these was set to imperial at the time of testing, despite no medicines or treatments having doses calculated in imperial units.”

Department of Health

The Department of Health has a system for issuing safety bulletins and procedure updates to hospital trusts known as Estates Alerts.

In early 2008, a series of bungled contradictory estates alerts were issued by the DH concerning medical weighing; all of which failed to recommend that all new scales should be metric-only.

The latest alert, issued 19 June 2008, countered advice given in previous alerts, but promised that “further guidance will be issued later in the year”. This advice has not been forthcoming.

In December 2009, the UK Weighing Federation announced that it is working with LACORS to push the Department of Health to issue the much-needed safety alert.


Exclusively metric units are used for all medical purposes.

All drug doses are in metric, and are often calculated per patient body mass (mg/kg), or per surface area (mg/m²).

Tracking a patient’s weight is not straight-forward using imperial units. e.g. Calculating 10% of 75 kg is a trivial task, but finding 10% of 12 st 9 lb is more prone to errors because it is not so simple.

Babies have been weighed in kilograms for decades, although in recent years metric readings have been dumbed down to pounds and ounces for the ‘benefit’ of grandparents, sometimes without the mother being informed of the original metric weight.



Interim report of the National Medical Weighing Project

Final report of the LACORS National Medical Weighing Project 2008/9

Department of Health Estates Alerts

DH (2008) 05 – Patient weigh scales

DH 2008/05U Patient weigh scales – update

DH (2008) 05(2U) – Patient Weigh Scales 2nd Updated http://www.dh.gov.uk/en/Publicationsandstatistics/Lettersandcirculars/Estatesalerts/DH_085724

13 thoughts on “NHS risking patients’ lives with imperial scales”

  1. It baffles me as to why people in the UK weigh themselves using both stones and pounds. The common practice in the USA is just to use pounds, which though not metric is at very least much simpler to keep track of.

    Since these are both a basic item and commonplace in the NHS would it not make more sense that a standard set of scales be used right across the NHS? Would that not be cheaper too?


  2. One of the ways to ‘encourage’ the use of metric-only scalepans would be for the maternity departments to refuse to give weights in pounds and ounces to parents. This an be justified on grounds that if in an emergency the baby has to be taken to a hospital that does not have access to the baby’s records, then they will have to rely on the parent’s own records. Changing from metric to imperial and back again is fraught with error situations which could endanger the baby’s health.

    Unfortunately this is unlikely to come about until there is a fatality as a result of ludicrous situation.


  3. This is truly criminal. In tandem with DfT’s slowness in recognizing the need for metric height and width restrictions (and its short-sightedness, now that it has “seen the light”, in insisting that both units appear on the same sign, thus making eventual conversion to metric-only signs that much more difficult), this demonstrates unequivocally that the government is too fearful of a small minority’s vocal opposition even in those areas where health and safety concerns should be paramount.

    Does anyone know how this issue is handled in the Republic of Ireland? Are all scales in doctor’s offices and hospitals already metric-only? I also wonder how this is handled in Canada, another bastion of muddledom!


  4. One way to kick-start this change may be to put the authorities on notice that if any harm comes from confusion over units, the UK Metric Association will take legal action for negligence. The threat of legal action may have greater impact than any amount of letters to newspapers and politicians.


  5. Similar evidence for the everyday nature of medical errors can be found in the USA. We don’t know how many of these errors arise from trying to convert stones or pounds into kilograms or from trying to convert milligrams into teaspoons. Evidence from the USA includes:


    where they write:

    The definitive study on the problem, which served as a wake-up call, was a 1999 report by the Institute of Medicine of the National Academies. Titled “To Err Is Human: Building A Safer Health System,” it estimated that somewhere between 44,000 to 98,000 Americans die in hospitals each year as the result of medical errors. Just the lower estimate would make medical errors the eighth leading cause of death at the time (more than motor vehicle accidents, breast cancer or AIDS).



    where they write:

    CHICAGO (Reuters) – Children with cancer often get the wrong dose of chemotherapy or are given the drug at the wrong time, and many require treatment because of the errors, U.S. researchers said on Friday.

    The problem has a lot to do with lack of common standards for delivering these life-saving, but highly toxic, drugs, said Dr. Marlene Miller, director of quality and safety at Johns Hopkins Children’s Center in Baltimore.

    Miller and colleagues evaluated data on medication errors collected in a national database from 1999 to 2004.

    They looked at a total of 829,492 errors reported in 29,802 patients.

    Of the errors, 310 involved kids on chemotherapy. Of those mistakes, 85 percent reached the patient, and nearly 16 percent of those were serious enough to require additional care.

    Miller likens the problem to the issues most parents face when trying to figure out how much of the analgesic ibuprofen to give a child because the dose must be calculated based on weight and age.

    “That is a reality for every single dose of medicine we give to children. There is no normal dose. There is no comfort level. There is no ability to say that is clearly, egregiously, too much for this age,” Miller said in a telephone interview.



    where they say:

    It was later discovered that the lead pharmacist on duty at the hospital the night before made a fatal mistake prescribing to Alyssa 330 milligrams of zinc, a nutritional supplement to help the baby’s metabolism, ABC reported.

    The dosage was 1,000 times the 330 micrograms of zinc that the baby was supposed to receive.



    where they say:

    Decimal errors can result in a 10-fold, 100-fold, or even 1,000-fold overdose or underdose

    A recent lawsuit alleges that a hospital patient received a 10-fold overdose of an analgesic, which resulted in a dangerous drop in blood pressure. As a result of an attempt to treat that condition, the patient became paralyzed and died. But it was the decimal error that apparently killed him.

    Decimal errors need not occur if you choose metric system prefixes so that hospital workers use whole numbers, see: http://www.metricationmatters.com/docs/WholeNumberRule.pdf


    Pat Naughtin
    Geelong, Australia


  6. In addition to Pat’s comments, the mess may be even greater in the US then in the UK but is more hidden. Even when large numbers of people are killed or seriously injured as a result of unit confusion there is no public outcry. Mostly because the cause of the errors is never seriously brought before the public eye. Could it be that blaming the continued use of non-metric units would not be considered acceptable to the US population? Would it be like blaming the US population for the errors simply because they reuse to metricate?

    Many of the prestigious hospitals, such as the Mayo Clinic in Rochester Minnesota have switched to full metric use to combat medical errors. But the hospitals that serve the common people are a mess. It is no wonder that so many injuries and deaths result. It seems that hospitals that cater to the rich and famous are more careful then those that cater to the common masses.

    Those who oppose metrication will blame the metric system for the ease at which decimal errors or prefix confusion can occur. But the real reason these errors occur is due to lack of familiarity with SI prefixes and working with decimal notation. Hospital personnel are trained to work with metric units in their education but that doesn’t mean they will learn it well or become proficient. They need to learn the units in school at a younger age and have the opportunity to use them daily as part of other measurements. Using grams and degrees Celsius inside the hospital environment and pounds and ounces outside is a disaster waiting to happen.

    Has there ever been a study to see if the same type of medical errors or level of medical errors occurs in hospitals in progressive countries that have always been metric?

    Whenever a medical error occurs in the hospital lawyers are quick to sue. Unfortunately the suits seldom address the source of the errors and a demand to correct them. If they did, then every hospital in the US would be working 100 % in SI and the burden of conversion to extinct units would be on the patient who would insist on them. It may be that hospital lawsuits are too much of a cash cow for the law suits to demand medical reform or else the source of easy revenue for the law firms would dry up.


  7. It would seem that no matter how serious the consequences of the measurement mess may be it is still not recognised as a fundamantal but solvable problem.

    Even the NASA report following the loss of the Mars climate orbiter did not lay the blame firmly at the door of the real issue.

    One has to suspect that if the solution makes the exclusive use of metric imperative some kind of prejudice overshadows it.


  8. In response to Phil, the problem is who do you blame? Do you blame the American and British populations who insist on hanging on to extinct units? It doesn’t make sense to blame an institution or business as these entities don’t make decisions on unit use. People within these entities make these decisions. The blame must be put on individuals that set up the rules if the rules they set up result in the errors.

    How could a court apply blame to people who make decisions that favour non-SI units even if they are the cause of injury and death if it is perceived that these non-SI units are the standard among the people? First you have to make laws that require the strict use of SI and for personnel to be tested for a working knowledge of SI before they can be allowed to work in that profession. Once you legally establish SI as the only allowable working system then and only then can you apply blame if errors occur if you can prove the error was cause by an individual violating the rules.

    The only prejudice that could result in making metric only imperative would come from those who would view any law requiring or favouring metric usage as going against the choice of the general population to use non-SI units and punishing them for that choice.


  9. Quote: “In December 2009, the UK Weighing Federation announced that it is working with LACORS to push the Department of Health to issue the much-needed safety alert.”

    How much power does the UK Weighing Federation have when it comes to deciding what type of scales or units on scales can be used or sold in the UK? If the UK Weighing Federation does have the right amount of pull, it would be simple for them to get an agreement among all companies producing and marketing weighing scales for the UK market to produce and provide scales that work only in SI units and stop providing scales that can be switched to other units. This would literally end the lingering use of extinct units.

    Even older scales that are periodically tested, repaired, recalibrated, etc., can at that time have their dual ability either removed or disabled. Making it impossible to service or replace non-SI scales would accelerate the demise of the lingering use of extinct units.

    This could also extend beyond hospital use. If it becomes impossible to purchase a dual scale for use in the markets, repair a broken imperial or dual scale or to recalibrate an older imperial scale, then the extinct units will die out quicker.

    I wonder how much contact the UKMA has with the UK Weighing Federation to help rid the UK of remnant scales using extinct units.


  10. I don’t understand why the Department of Health appears to be not taking this seriously.

    There were similar reports a few years ago involving blood glucose meters that were switchable between two different measurement units. There was no prevarication on the part of the authorities in that occasion.

    08 June 2006 – MHRA issues urgent safety warning about blood glucose meters

    “There have been a number of reports of adverse incidents where the units of measurement displayed on affected blood glucose meters have changed from mmol/L to mg/dL. Results displayed in mg/dL are 18 times higher than those expressed in mmol/L. The agency is concerned that this change in unit of measurement could lead users to think that the blood glucose result is high and thus alter the treatment regime, leading to self-administration of an insulin overdose and going into hypoglycaemic coma.”

    “The manufacturer will replace, free of charge, affected meters with new ones for which the unit of measurement cannot be changed.”

    Buyers’ guide – Blood glucose systems – May 2008

    Click to access Doc.aspx

    “MHRA recommends that the units of measurements for blood glucose systems in the UK are hard fixed to display results as mmol/l. Results expressed as mg/dl are higher by a factor of 18 than results expressed as mmol/l (ie 6.5 mmol/l will be expressed as 117 mg/dl). This could lead the user to think that the glucose result is high and thus alter the treatment regime.”

    The problem was easily understood, and the solution was simple. All glucose meters should only show standard measurement units. The same should apply to weighing scales, and any measuring device used to calculate drug or medication doses.


  11. I’m with Jerrimiah – and I think there should be a suitable – but not punitive – punishment when people use stones and pounds – like, for instance, not allowing them to have a lolly (candy) when they visit the doctor or making sure that they only get to see the tatty magazines in the waiting room – that sort of thing. It sounds minor but these little things encourage people to dislike stones and love kilograms.


  12. The obvious solution to this unacceptable situation is to just use metric. If anyone does not understand their weight in kilograms, medical staff can just tell them that a kilogram weighs the same as a standard bag of sugar that you can find in any supermarket. Hence patients can think of the number of kilograms that they weigh as the equivalent of a given number of bags of sugar. Simple!

    Perhaps if the government adopts the approach of the Think Metric website (http://www.thinkmetric.org.uk/) instead of supplying conversions, that would encourage people to think about their weight and height in metric units instead of relying on imperial conversions.


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