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:
http://www.netdoctor.co.uk/health_advice/facts/blooddonor.htm
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:
http://www.transfusionguidelines.org.uk/index.asp?Publication=NTC&Section=27&pageid=926
In reality the amount of blood in our bodies is proportional to weight. The guidelines given to hospitals can be seen here:
https://www.the-stationery-office.co.uk/nbs/rdbk2001/blood58.htm
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.
March 19th, 2007 at 00:29
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?
March 19th, 2007 at 20:07
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.
April 3rd, 2007 at 22:57
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]
June 12th, 2008 at 22:50
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.