# Why only O positive? **URL:** \ **Category:** Factual Questions\ **Created:** [September 13, 2001, 12:35am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208 "2001-09-13T00:35:04Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![GilaB](https://avatars.discourse-cdn.com/v4/letter/g/8e7dd6/32.png) [@GilaB](https://boards.straightdope.com/u/GilaB)\ **Post date:** [September 13, 2001, 12:35am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/1 "2001-09-13T00:35:04Z")
I’ve tried to donate blood several times over the last two days, but the blood centers are so swamped that they’re turning away “everybody who isn’t O positive”. I was under the impression the it was the O negs like me who were the universal donors. Is there any particular reason to take the O pos blood over O neg when prioritizing? ---
**Author:** ![The\_Peyote\_Coyote](https://avatars.discourse-cdn.com/v4/letter/t/5f8ce5/32.png) [@The\_Peyote\_Coyote](https://boards.straightdope.com/u/The_Peyote_Coyote)\ **Post date:** [September 13, 2001, 12:48am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/2 "2001-09-13T00:48:41Z")
I think you’re wrong Gila. I was always under the impression that O+ is the universal donor. ---
**Author:** ![Jadis](https://avatars.discourse-cdn.com/v4/letter/j/87869e/32.png) [@Jadis](https://boards.straightdope.com/u/Jadis)\ **Post date:** [September 13, 2001, 12:54am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/3 "2001-09-13T00:54:18Z")
People with a negative Rh factor cannot accept postive Rh factor blood, therefore any positive blood type cannot, by definition, be a “universal” doner. Since positive Rh factor people can handle negative Rh factor blood, it is O- that is the universal doner. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [September 13, 2001, 12:54am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/4 "2001-09-13T00:54:31Z")
Sounds like someone made a mistake. O+ blood can only be used by those with positive RH factor but O- can be used by anyone. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [September 13, 2001, 12:54am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/5 "2001-09-13T00:54:45Z")
O negative is the universal donor. But O positive is the most common type needed in an emergency and it is not uncommon for huge public response to fill the need for the other three types long before the need for O positive. Blood donation includes a lot of logistics that are not apparent to the average donor. Give blood next week. It will help every bit as much, and then give six weeks later, which will help even more. Everyone will be running short of all types in a couple of months. ## Tris “When people are free to do as they please, they usually imitate each other.” ~ Eric Hoffer ~ ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [September 13, 2001, 12:58am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/6 "2001-09-13T00:58:39Z")
By universal donor you mean among the O blood group, right? Mine’s AB, and I’m pretty sure I need AB blood. Peace, mangeorge ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [September 13, 2001, 1:05am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/7 "2001-09-13T01:05:09Z")
> [@](#): > > \*Originally posted by mangeorge \* > \*\*By universal donor you mean among the O blood group, right? Mine’s AB, and I’m pretty sure I need AB blood. > Peace, > mangeorge \*\* No, anyone can accept O blood, and AB types can accept anything. The A and B refer to proteins present in the blood–people with both are AB, and people with none are O. Your body will reject blood which has proteins that it doesn’t manufacture. That’s why O is the universal donor, and AB is the universal acceptor. At least I’m pretty sure that’s how it works. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [September 13, 2001, 1:06am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/8 "2001-09-13T01:06:19Z")
> [@](#): > > By universal donor you mean among the O blood group, right? Mine’s AB, and I’m pretty sure I need AB blood. > Peace, > mangeorge AB+ is the universal receprent. The ‘A’, ‘B’, and ‘+’ mean there is a particular protein? (well someting) on the blood cell. O- doesn’t have any of those ‘somethings’ so can given to anyone. AB+ has all of them so if given to someone w/o one or more they cause clotting. ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [September 13, 2001, 1:23am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/9 "2001-09-13T01:23:25Z")
Cool 🆒. So I can use any blood. 🙂 Wait a minute. That mean’s they’ll make me wait for AB, because nobody else can use it. Bummer. ☹ That’s ok guys. Just let me die. I don’t want to hog any of your precious O blood. Sniff. Peace, mangeorge (Useless blood guy) ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [September 13, 2001, 2:10am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/10 "2001-09-13T02:10:20Z")
‘A’, ‘B’, and ‘+’ refer to specific carbohyrdate moities on the surface of red blood cells. People lacking these sugars make antibodies against them. Thus, AB+ people have all three, make no antibodies against any of them, and can accept any blood. While O- lack all three, so other blood types have nothing for their antibodies to attack, and thus are the universal donors. ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [September 13, 2001, 3:14am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/11 "2001-09-13T03:14:44Z")
I’m O-, and I always get a slightly enthusiastic greeting at the blook bank. I get the scary feeling that sometime they’ll just hook me up to a permanent donation machine and make me a blood mine. :D:D:D ---
**Author:** ![Zot](https://avatars.discourse-cdn.com/v4/letter/z/e79b87/32.png) [@Zot](https://boards.straightdope.com/u/Zot)\ **Post date:** [September 13, 2001, 4:05am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/12 "2001-09-13T04:05:23Z")
When I tried to give at St Vincent’s in Manahattan yesterday, they were taking O- right away. For everyone else, including 0+ like me they were takling names and telephone numbers. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 13, 2001, 5:24am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/13 "2001-09-13T05:24:59Z")
> [@](#): > > \*Originally posted by Smeghead \* > ‘A’, ‘B’, and ‘+’ refer to specific carbohyrdate moities on the surface of red blood cells. Almost correct. A and B are two different sugar molecules attached to the same place on short chains of other sugar molecules on the surface of red blood cells. If you are AB, you have some of each. Rh positive is a protein that’s also on the surface of red blood cells. O- indicates you have neither sugar molecules nor the Rh protein. For those interested, the A sugar is N-acetylgalactosamine and the B sugar is galactose. ---
**Author:** ![Jdeforrest](https://avatars.discourse-cdn.com/v4/letter/j/49beb7/32.png) [@Jdeforrest](https://boards.straightdope.com/u/Jdeforrest)\ **Post date:** [September 13, 2001, 12:55pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/14 "2001-09-13T12:55:11Z")
On a side note, what are the rarest blood types? ---
**Author:** ![amarinth](https://avatars.discourse-cdn.com/v4/letter/a/3be4f8/32.png) [@amarinth](https://boards.straightdope.com/u/amarinth)\ **Post date:** [September 13, 2001, 1:09pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/15 "2001-09-13T13:09:43Z")
from [http://www.psbc.org/education/hematology/banking/\_frm/frm\_typing.htm](http://www.psbc.org/education/hematology/banking/_frm/frm_typing.htm) AB- .5% B- 2% AB+ 2.5% B+ 8% A- 8% O- 9% A+ 34% O+ 36% ---
**Author:** ![Superdude](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/superdude/32/13450_2.png) [@Superdude](https://boards.straightdope.com/u/Superdude)\ **Post date:** [September 13, 2001, 1:31pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/16 "2001-09-13T13:31:28Z")
I’m O+. But I can’t donate because of a tattoo I got almost a month ago. I have to have it for a year to make sure there’s no infection. ---
**Author:** ![TheeGrumpy](https://avatars.discourse-cdn.com/v4/letter/t/779978/32.png) [@TheeGrumpy](https://boards.straightdope.com/u/TheeGrumpy)\ **Post date:** [September 13, 2001, 10:31pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/17 "2001-09-13T22:31:40Z")
> [@](#): > > posted by Triskadecamus: > \*\*Give blood next week. It will help every bit as much, and then give six weeks later, which will help even more. \*\* A noble sentiment, but isn’t the usual waiting period _eight_ weeks? > [@](#): > > posted by AWB: > **I’m O-, and I always get a slightly enthusiastic greeting at the blook [sic] bank. > I get the scary feeling that sometime they’ll just hook me up to a permanent donation machine and make me a blood mine** On another side note, won’t it be handy to develop cloned marrow that can churn out various types on demand? I guess there are some blood substitutes available now, but a cloned product is probably only a decade away. (Less is there’s a major war in the near future.) ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [September 13, 2001, 10:41pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/18 "2001-09-13T22:41:13Z")
> [@](#): > > \*Originally posted by TheeGrumpy \* > On another side note, won’t it be handy to develop cloned marrow that can churn out various types on demand? I guess there are some blood substitutes available now, but a cloned product is probably only a decade away. (Less is there’s a major war in the near future.) This has been a dream for a long time. If there was a way to make blood artificially there would be no need for blood drives. Unfortunately no one has found a way to do it (yet.) I am confident that this is something that could be invented within my lifetime. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [September 13, 2001, 10:54pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/19 "2001-09-13T22:54:24Z")
I’m AB+ too. AB blood is only good for the 2% of the population who is also AB, so it is not really in much demand since AB people can take any blood that happens to by lying around. So if you’re AB, offer to donate plasma. It takes about an hour. They strap you down, and drain your blood, centrifuge it, and replace the blood cells back into your body. Plasma is probably in great demand right now, so make sure you tell the blood bank people you’re AB and want to donate plasma. Oh, also plasma has a very long shelf life, while whole blood is only good for a month or so. So if the banks are filled with whole blood everyone can still donate plasma, which doesn’t have to be used right away. And if you can wait, the best time to donate blood will be a month from now, when the current wave of blood is starting to go bad. That’s when we’ll need blood most. ---
**Author:** ![Mtgman](https://avatars.discourse-cdn.com/v4/letter/m/b5a626/32.png) [@Mtgman](https://boards.straightdope.com/u/Mtgman)\ **Post date:** [September 14, 2001, 3:23am UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/20 "2001-09-14T03:23:28Z")
> [@](#): > > \*Originally posted by Lemur866 \* > \*\*So if you’re AB, offer to donate plasma. It takes about an hour. They strap you down, and drain your blood, centrifuge it, and replace the blood cells back into your body. Plasma is probably in great demand right now, so make sure you tell the blood bank people you’re AB and want to donate plasma. > > Oh, also plasma has a very long shelf life, while whole blood is only good for a month or so. So if the banks are filled with whole blood everyone can still donate plasma, which doesn’t have to be used right away. > > And if you can wait, the best time to donate blood will be a month from now, when the current wave of blood is starting to go bad. That’s when we’ll need blood most. \*\* My local center wasn’t taking plasma donations even though it is one of their top goals to try to get more plasma donations. The reason? There were to many people in line. They can’t take time out to do the more complex procedure to collect plasma when there are a hundred plus people waiting to donate. Plasma does indeed have a long shelf-life. You can freeze plasma and it will keep up to a YEAR. Whole blood is generally unusable after 35 days, less if the patient is already in poor condition because a large number of the blood cells will have died. One of the most desperately needed blood products during times of emergency is platelets. They have an incredibly short shelf life, but contain a very high concentration of the cell bodies which cause clotting and are therefore good in cases of internal bleeding and other injuries. Steven [Next page](https://boards.straightdope.com/t/why-only-o-positive/81208.md?page=2)