Euric, That's the nominal volume of a unit of blood but nobody I know of uses volumetric measurement to determine when that much has been donated. Back in the glass bottle days there probably was a line on the bottle, but even then it was determined by mass (in the late '60s).
When plastic collection bags were introduced, and possibly before, a trip balance was used to determine that the proper amount has been donated. You can see this for yourself if you donate to the Red Cross. They hang the collection bag on one arm of the counterweighted trip balance and when it has sufficient mass the trip balance trips (tips the other way). When you hear that "thunk", you are done. In the U.S., the FDA is the regulatory agency that governs blood collection. On the web, you can read this FDA page: http://www.fda.gov/ora/inspect_ref/igs/blood.html#PART A - WHOLE BLOOD DONOR Specifically, under "Blood collection" it says: "The completion of the donation may be signaled by a trip scale or vacuum-assist method based on mass or volume. Otherwise, the bag must be weighed (spring scales) and the flow stopped manually. The blood should be mixed gently (either manually or mechanically) during collection. The final unit should weigh approximately 425-525 grams plus the weight of the container and anticoagulant (approximately 90 grams)." I watch the Red Cross personnel log in the units of blood that they have collected and as they box them up for transportation. They use a scale to check the mass of the container and blood (and anticoagulant). I have not seen them measure the volume. The range of masses allows for variations in hematocrit levels and also provides some leeway in case someone's donation must be stopped just a little early. The average density of blood ("specific gravity" is the term misused on the page linked above) is 1.053 kg/L. So 450 mL would have a mass of about 474 g. Notice that this is right in the middle of the mass range shown above. But, assuming this density value, the actual volume of blood in an acceptable unit might range in volume from 404 mL to 499 mL. Of course, if the density of the blood in one particular unit varies from 1.053 kg/L, due to variations in hematocrit levels for example, then the volume might vary even more. Interestingly, the FDA speaks loosely in other sections about a unit of blood having a volume of 500 mL, but this is the section that sets the specification. In fact, 500 mL is right at or just beyond the maximum mass specification at standard density. So, 450 mL is nominal volume, but that may vary. Mass is the parameter actually measured. You're right. I last presented this on the USMA list on 2000-09-09 --- before you joined us. I hope that this information helps and that my description of the procedure makes sense to you. Jim On Tuesday 2004 August 17 18:02, Euric wrote: > ----- Original Message ----- > From: [EMAIL PROTECTED] > To: [EMAIL PROTECTED] > Sent: Tuesday, 2004-08-17 16:33 > Subject: FW: pints of blood > > > Dear Euric, > > > > Thank you for your email inquiry regarding the measurement of a pint of > blood. > > > > In the scientific community there was by necessity a need to have > standardization of units of measurements, hence the metric system. > > The system was developed in Europe long ago. The blood banking community > follows the European metric system meaning that a > > unit of blood is 450 mls. > > > > We communicate this as a "pint" to explain the 450 mls since we are not a > country that universally follows the metric system and a > > pint is easier to understand. Yes a blood donation is slightly less than a > pint. > > > > Again, thank you for your inquiry. > > > > > > Rosemary Leyland > > Director, Corporate and Community Development > > Ã American Red Cross Blood Services > > Penn-Jersey Region > > (Voice: 215-451-4051 > > (Cell: 1-215-687-8690 > > Fax: 1-215-451-2546 > > [EMAIL PROTECTED] > > > > > > > > -----Original Message----- > From: Euric [mailto:[EMAIL PROTECTED] > Sent: Saturday, August 07, 2004 1:15 PM > To: Kane, Kristy > Subject: pints of blood > > > > If I donate a pint, how much blood am I really donating? > > > > The collection bags hold 450 mL of product. The standard US pint is 473 > mL. When you say pint, do you mean 473 mL or the 450 mL the bag holds. > What means do you use to measure a pint? > > > > When you say gallon, do you mean 3.785 L based on a 473 mL pint, or do you > mean 3.6 L, based on the 450 mL capacity of the bag? > > > > Below you mention a donor who has given 24 gallons. How much did he > actually give? Based on the standard definition of the gallon, that would > be 91 L. Based on the amount of blood held in the bags, that would be > about 86.5 L. That is a 4.5 L difference in the two meanings. > > > > I'm just curious to know how you determine the amount of blood in a pint > and gallon. > > > > > > > > > > American Red Cross Recognizes 24 Gallon Blood Donor > > > > > > Philadelphia, PA, April 29th, 2004 - > > Montgomery County's Hal Kellogg Has Been Donating Blood for 70 Years > > Proving that there is no age limit to donate blood, Howard "Hal" > Kellogg recently gave his 24 gallon blood donation for the American Red > Cross at the age of 88. > > > > > > > > > Thanks, > > > > Euric -- James R. Frysinger Lifetime Certified Advanced Metrication Specialist Senior Member, IEEE http://www.cofc.edu/~frysingj [EMAIL PROTECTED] [EMAIL PROTECTED] Office: Physics Lab Manager, Lecturer Dept. of Physics and Astronomy University/College of Charleston 66 George Street Charleston, SC 29424 843.953.7644 (phone) 843.953.4824 (FAX) Home: 10 Captiva Row Charleston, SC 29407 843.225.0805
