Blood transconfusion

The National Blood Service are understandably concerned that not enough people are coming forward to donate blood. There are, no doubt, a variety of reasons why people are inhibitied from doing so, e.g. can’t spare the time, nervousness about the procedure etc.

I wonder though whether the information about the amount of blood taken at each session may be a factor.

(Article by Phil Hall)

Consider the advice given on this web site:

In particular I draw attention to the following extracts:

(1) “How much is a unit?

One unit of blood equals is 450ml (just under a pint).
An adult’s body contains around 8-10 pints of blood.”

(2) “If you pass the test for anaemia, you can donate one unit of blood.
This represents only 10-12 per cent of the amount of blood in an
adult, and the body quickly makes good the loss.”

Firstly, that phrase “just under a pint” is potentially misleading. 450 ml is in fact 21% “under a pint” (assuming a UK pint of 568 ml) which is quite significant.

Secondly statements (1) and (2) don’t add up.

450 ml is 8% of 10 pints and 10% of 8 pints so it would be more accurate to say it represents 8-10 percent of the amount of blood in an adult based on the figures given earlier.

This confusion could be avoided if the information is given in ml, litres only so that the proportions are obvious.

The National Blood Transfusion service actually uses an average figure of 5 litres for the purposes of calculating percentage blood loss:

In reality the amount of blood in our bodies is proportional to weight. The guidelines given to hospitals can be seen here:

where a proportion of 70 ml/kg means that for most people a unit of blood is 9% or less of the total blood in their body.

The litre and the kilogram are nowadays quite familiar units to people in the UK. There is no need for the pint and the crude conversions we see above only exaggerate the amount of blood people are being asked to give in each session.

It may or may not be a significant factor in putting people off giving blood but surely from a PR point of view it is foolish to overstate it.

Author: UK Metric Association

Campaigning for a single, rational system of measurement

17 thoughts on “Blood transconfusion”

  1. The pint in the UK is defined as 568 ml. So what definition do the National Blood Service use? Or are they just really bad at maths.

    A change to everything in metric would certainly help here, as saying they take 450 ml (just under a pint) is clearly misleading, if not fraudulent.

    Probably they do not know what a pint is in this country (perhaps they do not drink beer in pubs at all nor have milk delivered, last time I looked milk bottles are labelled as 1 pint 568 ml, and some beer glasses are labelled that way too), which suggests they also might take a wrong amount of blood from a person. I currently will not consider donating blood as they take so much, and if they really did want to take nearly a pint, perhaps 550 ml, that is too much. 450 ml is over 100 ml less than a pint.

    Maybe I should say to them I weigh just under a tonne. If they are going to use an illegal definition of a pint which they have made up, then I can make up anything if I were to go and donate blood, surely?


  2. In answer to a comment made above I would like to make it clear that the article is in no way intended as a criticism of the National Blood Service practices.

    The NBS are doing a vitally important job and it is essential that healthy people come forward to give blood. A unit of blood is scaled to be completely safe for all volunteers who qualify.

    The point of the article is about the quality of published information in respect of measurement data and the potential harm that the continued use of an obsolete unit like the pint can do to the campaign for recruiting volunteers.

    I would also point out that this example is not the only case where measurement information given in NHS literature is being compromised by archaic units in the misguided belief that the public will be better informed as a result. Future articles will be dealing with this matter in other health related areas.


  3. I just want to add that I do not want to put off anyone from donating blood. Just that, by incompetent or inaccurate conversions from metric to imperial, the people responsible for taking it might be misleading you about the amount you donate. [Comment has been edited]


  4. One UK pint is about 568.261485 ml, and
    One US pint is about 473.176473 ml.

    Here in the US, 450 ml really does seem just under a pint (~4.9% less). My question is why 450 ml, why not an even half liter for a unit of blood.


  5. I was just wondering why UK went metric but still uses the imperial units. Just wondering.


  6. The information on the website is clearly inaccurate for a British audience.

    450ml is more than 20% smaller than an Imperial pint of 568ml. I think the web page authors have confused the Imperial pint with the US pint of about 473ml.

    There is a complaint mechanism on the web page at and it would be a good idea if the UKMA made an official complaint. (Even the British Weights and Measures Association should be up in arms about this one, as a British web page has used American measures!)


  7. Michael Glass says: 2015-06-13 at 14:14
    “The information on the website is clearly inaccurate for a British audience.”

    An interesting point. As the legal units of measures in UK are metric (apart from those that are specified), then as a point of law, would there be any difference between using pints, pounds or ounces of any description, as each would be of equal wrongness? It is after all ‘only a description’ as accepted by government. If this helps confuse people to the point where change is deemed necessary then it is all to the benefit of the metric cause. In any case, anything NHS related should be metric.


  8. @BrianAC
    It is totally misleading to say “the legal units of measures in UK are metric (apart from those that are specified)”. In the UK you can legally use whatever units of measure you like, except for certain regulated activities, and they are mostly related to the sale of goods by measure and government administration.

    I can legally sell a 40-inch television, 2 pounds of apples, 1-acre of land or a 25-gallon water tank. However, with the apples (and only if they are priced by weight) to comply with the law I must additionally give their price per kg alongside the price by any other weight unit I choose.


  9. But may you LEGALLY use a pound scale to weigh those apples or must it be metric? I am asking about the law, not whether you will get away with it because TSO has given up. Will the acre of land be REGISTERED as a fraction of a hectare (or square meters)?


  10. Charlie P writes: ‘I can legally sell a 40-inch television, 2 pounds of apples, 1-acre of land or a 25-gallon water tank. However, with the apples (and only if they are priced by weight) to comply with the law I must additionally give their price per kg alongside the price by any other weight unit I choose.’

    Yes, you can describe your television as 40-inch because you are not selling it by the inch, you can sell a bag, box or bowl containing two pounds in weight of apples if you are selling by the bag, box or bowl and are not weighing the apples out on scales, you can describe your land area (and advertise it) as one acre but you cannot register the sale and ownership of the land as one acre, you have to use metric units, and you can describe your water tank as 25 gallon as you are not selling it by the gallon. You can also sell a ten-gallon hat by that name for the same reason (despite the fact it would be a ten US gallon hat). But your last sentence is misleading: if you are pricing your apples by weight, it is not the case that you must ‘*additionally* give their price per kg alongside the price by any other weight unit I choose’ (my emphasis). The first price shown, the legally binding price, must be per kg and it is not *additional* to anything. It is not necessary to show any other indication besides the legally binding price per legal unit of weight. If you choose to show a price by any other weight you choose (how weird is that?), or even by imperial unit, which is presumably what you mean, that secondary information has no legal value – and that is an important difference. It is thus redundant (except to people who only understand the ‘other weight unit’ you have chosen, or imperial, if that is what you meant). I think most people who follow this subject know how the law in the UK stands on indication of weight. Yes, you are legally entitled to describe many things any way you like if you are not selling by weight or measure, but that is not in dispute. What is in dispute is that the metric unit is in any way *additional* to any other unit of weight that may or may not be displayed. It is not additional to anything. The converse is the case: if any other unit is shown, then that unit is the additional unit. But I think you really really know that already.


  11. @John Steele
    You are narrowing, as well as moving, the goal posts now by concentrating only on the limited activities for which there are legal requirements.

    As I said, the statement “the legal units of measures in UK are metric (apart from those that are specified)” is totally misleading. In general, units of measure are not regulated in the UK, so, in general, you can use whatever units you like. As I also said, there are however certain specific circumstances in which metric units must accompany any other units used, mostly related to the sale of goods by measure and government administration.

    Selling apples by the pound will fall into the exception for selling by weight, and yes, will thus require scales capable of displaying metric measures in addition to imperial. I imagine that the land registry (probably falling into the exception for government administration) now record transactions in metric units, but that doesn’t mean that land cannot legally be sold in acres.

    So rather than concentrating on the exceptions, why not accept that in most applications the choice of units of measure is not legally restricted in the UK.


  12. @ Charlie P says:2015-06-15 at 10:08
    “However, with the apples (and only if they are priced by weight) to comply with the law I must additionally give their price per kg alongside the price by any other weight unit I choose.”

    Great, so far you agree with me. The point I made was exactly as you say “alongside the price by any other weight unit I choose.” We are still in total agreement here. So if you were to sell this 25 gallon water tank, but it was a 25 US gallon tank, that would be just fine, totally honest, it was ‘just a description’ (approved by UK ministers). If you were to sell a pint measuring jug and it was an American pint jug that would also be fine and dandy. If you were to sell these pounds of apples and you used the troy pound, that also would be a nice little earner, golden delicious in fact, it is only a supplementary indicator.
    The NHS using US pints instead of UK pints (One unit of blood equals is 450ml (just under a pint). Read more: They can’t even get the English right, let alone the arithmetic.

    (450ml = 0.951019388 US pints (just under) but 0.791888967 Imperial pints (quite a bit under)) is then quite acceptable to you. On that point we tend to disagree. You would be quite happy for the NHS to give you or your family the wrong amount of anything, the doctor giving one measure, the nurse using a different measure (of the same unit). Now this is only the US/UK divide, bring in all nationalities of the planet into the mix and see what happens if they all use ‘whatever measure they know best’.

    IMHO the best way is to find a set of measuring units that the whole world could use and understand, then use that system for all purposes, at all times, by everyone.


  13. @Charlie P:

    Your intransigence is tiresome to say the least. What are you trying to achieve? If you want to sabotage our children’s future, then, yes, that is something that you may well be achieving. But if you want a Britain that can make its way in an ever increasingly competitive (and metric) world, then you are not doing anyone any favours. Why not just accept the fact that over 95% of the world’s population speaks only metric, and end your pedantic arguments that just cause confusion for so many and elicit comments such as that above from Situmbeko Sitwala.


  14. I think it’s a pity that this whole discussion has got way off topic. The National Blood Service has made a mess of the units and this should be brought to the attention of those responsible.

    Because the National Blood Service made an obvious error there should be no problem in sorting it out. After all, this is a medical site and it is essential that they have their facts right. I hope that they would be grateful for the advice and will act on it quickly.


  15. Charlie P wrote. “Selling apples by the pound will fall into the exception for selling by weight, and yes, will thus require scales capable of displaying metric measures in addition to imperial.”

    Charlie, there is no legal requirement for scales in the UK to display anything but metric measures. You are wrong when you say they must also show imperial. Do not forget: a sale is a legal transaction governed by law. The law recognises only metric units as the basis of a sale. Your ‘additional’ imperial unit is for information for those people who cannot (or today probably more likely will not) accept that they understand the metric units. There is no legal requirement for anything but the legal units. This is obvious to anybody who knows anything about this subject. What you are effectively claiming (in your later replies) is that weights and measures are used in a total vacuum to which there are ‘exceptions’ for ‘certain specific circumstances’ or ‘limited activities for which there are legal requirements’, as you put it. If you wish to cram the whole of the UK economy where weights and measures are involved (and I am thinking of areas other than simply selling apples) into the bracket of ‘exceptions’, then you are in effect turning the law upside down. I prefer to think that the law exists to protect all parties to any transaction, even to the buying of apples by weight, not that I am involved in an ‘exceptional circumstance’ where a provision of law simply happens to apply. You are in fact saying there is no such thing as the law except in those ‘very few areas’ where laws exist. Those ‘very few areas’ are vast indeed, my friend.


  16. @ JFL

    You seem to be missing the point about Charlie P. He is not discussing the merits (or otherwise) of having a single system of measurements to boost Britain’s position in an increasingly globalised world.. His agenda *is* pedantry and point scoring on what he sees as a libertarian platform.

    [As Michael Glass has remarked this thread has gone way off topic, and the exchanges with Charlie P are becoming very tedious. No further comments will be posted, so THIS CORRESPONDENCE IS THEREFORE AT AN END! – Editor]


  17. I’ve seen other howlers made by the NBS in their use (or rather non-use) of the 24-hour clock. A notice outside one donation venue said that the next session would begin at “04:30 pm”. Wrong! Half-past four written with four digits is either 04:30 or 16:30.

    Does it matter? I would say it is worrying for members of the medical profession not to be conversant with the 24-hour clock. If you’re dealing with an in-patient who requires medicating at specific intervals, knowing the unambiguous time of their last dosage could make all the difference between under- and overdosing.

    Tintin fans may recall how, in ‘Explorers on the Moon’, it was the Thompson twins’ failure to distinguish between 1:34 am and 1:34 pm that led to them stowing away on the rocket, thus putting a dangerous strain on the oxygen supply.


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