# 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:** 5\ **Page:** 2
**Author:** ![absimia](https://avatars.discourse-cdn.com/v4/letter/a/bbe5ce/32.png) [@absimia](https://boards.straightdope.com/u/absimia)\ **Post date:** [September 14, 2001, 1:43pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/21 "2001-09-14T13:43:58Z")
And, even better, you can donate plasma twice a week. Gallons of your bodily fluids could be distributed nationwide in very short order. Steven, how would one go about donating platlets? Is it just spun out of whole blood? Back in my lean college days I sold my plasma ($10 first visit, $15 second visit a week), but had to stop because (according to the fella who ran the machines) my blood clotted quickly and would gum up their machine. Guess I have lots of platelets to spare. Absimia ---
**Author:** ![artemis](https://avatars.discourse-cdn.com/v4/letter/a/91b2a8/32.png) [@artemis](https://boards.straightdope.com/u/artemis)\ **Post date:** [September 14, 2001, 2:39pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/22 "2001-09-14T14:39:55Z")
You can donate platelets by cytopheresis; they hook you up to a machine that works like a giant centrifuge, spining the blood to separate it into components, collecting the platelets, and returning the rest of the blood components to your body. The process takes about 2 hours, and you can donate every 2 weeks or so. Platelets can also be obtained from regular whole blood donations; after the blood is donated, they usually separate it into packed red cells, plasma (which is frozen), and platelets. You need to combine the platelets from several units of blood to have enough to transfuse into a patient, though, and a whole blood donor has to wait at least 8 weeks before he/she can donate blood again, so it’s not as efficient a way to get platelets as cytopheresis is. Artemis ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [September 14, 2001, 4:33pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/23 "2001-09-14T16:33:21Z")
```auto B Rh A 0 1 0 36.0 0 1 1 34.0 0 0 0 9.0 0 0 1 8.0 1 1 0 8.0 1 1 1 2.5 1 0 0 2.0 1 0 1 0.5 ``` (The standard code used is unfortunate, I am using + or - for each factor, not just Rh)We can see B- make up 87% while only 13% are B+. Next is Rh. B-Rh+ make up 70% of the total, almost equally divided between A- and A+: B-Rh+A- 36%, B-Rh+A+ 34% If you are B- then your chances of being A+ are about equal. If you are B+ then your are four times more likely to be A- Everything else being equal you are much more likey to be Rh+ I guess I am quite normal being B-A+Rh+ ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [September 18, 2001, 4:35pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/24 "2001-09-18T16:35:19Z")
> [@](#): > > \*Originally posted by sailor \* > \*\*_If you are B- then your chances of being A+ are about equal. If you are B+ then your are four times more likely to be A-_ > \*\* Huh? If someone is B-, the chances of them being A+ is 0%. The chance of them being B- is 100%. ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [September 18, 2001, 5:12pm UTC](https://boards.straightdope.com/t/why-only-o-positive/81208/25 "2001-09-18T17:12:38Z")
Sailor is talking about the individual factors (A, B, Rh). Since my **blood type,** like Sailor’s, is “A-positive,” my blood cells include the following factors: A Rh My blood does NOT contain “B” factors. Were I type “A-negative,” my blood would contain ONLY “A” factors. Breaking it down like this makes it a bit clearer as to who can accept what blood, I think (stay away from me, Bs and ABs! All Type-As and Type-Os–positive or negative–are welcome, though). [Previous page](https://boards.straightdope.com/t/why-only-o-positive/81208.md?page=1)