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.