# Blood donors and bleeding **URL:** \ **Category:** Factual Questions\ **Created:** [July 28, 2009, 8:13pm UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586 "2009-07-28T20:13:25Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![ZipperJJ](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zipperjj/32/211_2.png) [@ZipperJJ](https://boards.straightdope.com/u/ZipperJJ)\ **Post date:** [July 28, 2009, 8:13pm UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586/1 "2009-07-28T20:13:25Z")
If I donate blood and then get in a car accident on the way home (wherein I have bleeding wounds), how important is it for the medical people who take care of me to know that I’ve just given blood? How about a day after donating, or a week? Should I walk around sporting my “I Make a Difference” sticker for a a while, for my own safety? Other than the not-always-obvious hole in my arm, can a doctor tell when someone is about a pint short of blood? ---
**Author:** ![Birdmonster](https://avatars.discourse-cdn.com/v4/letter/b/71e660/32.png) [@Birdmonster](https://boards.straightdope.com/u/Birdmonster)\ **Post date:** [July 28, 2009, 8:21pm UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586/2 "2009-07-28T20:21:38Z")
According to this [American Red Cross FAQ](http://www.givelife2.org/donor/faq.asp#10), it takes 24 hours for your body to replenish its lost blood. So after 24 hours, no sticker necessary. I will say, personally, it gets me real woozy for about an hour and a half, and I usually feel normal the next morning. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 28, 2009, 8:35pm UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586/3 "2009-07-28T20:35:51Z")
> [@Birdmonster](#): > > According to this [American Red Cross FAQ](http://www.givelife2.org/donor/faq.asp#10), it takes 24 hours for your body to replenish its lost blood. So after 24 hours, no sticker necessary. This may or may not be an important distinction, but the fluid volume is what gets replaced in a day’s time; the red blood cells and other components take considerably longer, which is why they make you wait 8 weeks between donations. I’m not a doctor, but my layman’s understanding is that when someone is bleeding out, restoration of the missing volume is of primary importance, and so saline fluid can be used if blood of correct type is not immediately available, and that it’s OK if a bleeding victim is left \ anemic by this. If you’re already missing a pint’s worth of red blood cells when you have your car accident, I wonder what the consequences are if they try to restore your missing volume with saline, diluting your already-diluted blood? ---
**Author:** ![Birdmonster](https://avatars.discourse-cdn.com/v4/letter/b/71e660/32.png) [@Birdmonster](https://boards.straightdope.com/u/Birdmonster)\ **Post date:** [July 28, 2009, 8:40pm UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586/4 "2009-07-28T20:40:28Z")
**JFF** ’s distinction is good. FAQ definitely did say lost “fluid” not blood, which, as noted, are not the same. My bad. ---
**Author:** ![Swallowed\_My\_Cellphone](https://avatars.discourse-cdn.com/v4/letter/s/9d8465/32.png) [@Swallowed\_My\_Cellphone](https://boards.straightdope.com/u/Swallowed_My_Cellphone)\ **Post date:** [July 28, 2009, 10:30pm UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586/5 "2009-07-28T22:30:30Z")
Don’t they draw some blood to type and match? I would think that you’d get to the hospital, they’d go “Wow! That’s a really low red blood count! We need a couple units of whole blood there.” When I donate platelets, they seem to be able to tell me my HCT and HGB within minutes. Don’t know about the paramedics adding fluids though. ---
**Author:** ![Nunavut\_Boy](https://avatars.discourse-cdn.com/v4/letter/n/e95f7d/32.png) [@Nunavut\_Boy](https://boards.straightdope.com/u/Nunavut_Boy)\ **Post date:** [July 28, 2009, 11:10pm UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586/6 "2009-07-28T23:10:47Z")
Depending on how much time has passed, they won’t even detect the blood loss of the donation at the hospital. This is because when you donate blood, you lose equal amounts of cells and fluid, so the relative proportion of cells/plasma is the same as before you donated. The technology used to determine hemoglobin and cell counts relies on this cell/plasma ratio to calculate results. So depending on how long ago you donated and how many fluids you’ve been drinking, your blood cell loss may be undetectable. Further, the average human male’s blood supply (cells + fluid) is about 6 litres. One blood donation is about 500ml, leaving you with 5.5L or about 92% of your original blood volume. Assuming you’re normal and have no hematological oddities, that 92% will likely still be in the normal range, even if we could measure absolute amounts of the different components of blood, which we can’t. AND, if you’re in some accident and bleeding acutely, volume is more of an immediate concern than O2 carrying capacity. The paramedics/ER will likely give pentaspan or some other colloidal solution (in real life possibly at the same time as RBC units, if you’re in a hospital) so that you have something to pump. If you’re bleeding that bad, they don’t wait around to measure things. They phone for ‘O negs STAT!’ just like on TV. ---
**Author:** ![ZipperJJ](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zipperjj/32/211_2.png) [@ZipperJJ](https://boards.straightdope.com/u/ZipperJJ)\ **Post date:** [July 29, 2009, 1:26am UTC](https://boards.straightdope.com/t/blood-donors-and-bleeding/504586/7 "2009-07-29T01:26:51Z")
Thanks, **Nunavut Boy**. So what you’re saying is that if I need more blood, I need more blood, and it’ll be noted and taken care of. But I probably won’t need more blood than I would have had I not just donated. Having just donated is not some secret emergency thing I’d need to announce like being diabetic or being on certain drugs. Gotcha. I can rest easy now 🙂