So, I gave blood today, as is my habit about every 112 days, going on the apharesis machine to do a double red cell donation. After the donation, as usual, I found myself having to urinate more often than usual. That's when it struck me. They still give the advice to be well hydrated before donation (and to eat a good meal), but the double red cell donation has the fluid being taken out replaced by saline solution before it's injected back in. Is drinking a few extra glasses of water before an apharesis donation necessary or even recommended?

  • This is a questions where a little prior research -- which is required here -- would have saved you two bounty awards. The standard advice found on almost all authoritative sites is to be well hydrated and to eat well before donation. There doesn't appear to be a recommendation to increase hydration above normal levels from any source. So an extra glass of water or two isn't going to do you any harm, but it's also not necessary if you're otherwise normally hydrated.
    – Carey Gregory
    Jan 18, 2022 at 1:49
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    @careyGregory I agree that that's what's advised, bit it's also the advice I've always received before any blood donation, and when I'd asked the workers, they said that they had no idea if the advice to hydrate was as necessary as a whole blood donation. As for the bounty, it's internet points, no great loss. :) Jan 18, 2022 at 3:09
  • Okay, but please understand that I'm not closing your question only because it was asked when the prior research requirement wasn't enforced as strictly, and I figured a 150 point penalty is punishment enough. What I learned in 5-10 minutes of searching was that over-hydrating wasn't recommended by anyone for either type of donation.
    – Carey Gregory
    Jan 18, 2022 at 4:48

2 Answers 2


I agree with the comment by Carey Gregory that the answer was available online had you done more prior research, but ironically this specific question of yours was the first result suggested by Google. Also, even though so many websites offer information about this topic, there doesn't yet seem to exist a single page that summarizes all the important points from those various websites, so I will do that here.

What is a double red cell donation?

The donor's blood is removed and red blood cells (RBCs) are separated from the plasma and platelets. The plasma and platelets are then inserted back into the donor's body, since it's just the RBCs that are being donated, and there's no need to permanently take away the donor's plasma and platelets. However, because RBCs have now been removed, the blood's volume has been reduced, so a saline solution is added before the plasma and platelets are given back to the donor: this is to replace the lost blood volume. By doing this, the recipient can get about twice as much blood from the same donor, which can reduce the number of donors to whom they get exposed (i.e. it's safer for the recipient); and the donor also benefits from not having to go as frequently, through all the inconveniences of donating blood.

Why is hydrating before donating blood advised (in general)?

Northwestern Medicine says:

"Since your body is made mostly of water, it’s important to stay hydrated before (and after) giving blood. A loss of fluids can lead to a drop in your blood pressure, which explains why some may feel dizziness. Be sure to drink at least two cups before you donate. You’ll also feel better if you have something in your stomach, which also stabilizes your blood pressure."

The Complete Care Hospital says:

"Drink water: A good portion of the blood donated is made up of water, so be sure to drink water before and after donating. Most locations advise drinking about 16 ounces of water beforehand. This will help reduce fatigue and dizziness after donating by keeping your body hydrated and replenished."

The SLMA says:

"Donating blood increases the risk of dehydration [...]. Blood volume recovers fairly quickly for people who stay hydrated,"

All three of the above sources state that the reason why you're advised to be reasonably well-hydrated before donating blood is because you lose a lot of blood volume, and water is a major constituent of blood, therefore you lose a lot of water and can therefore experience symptoms of dehydration (e.g. dizziness)

But what about for double red cell donation (specifically)?

It was mentioned above that plasma (which contains water) and platelets are returned to the donor during a double red cell donation, plus an additional saline solution, so isn't blood volume loss not longer a problem for donors doing through this extra procedure?

Indeed, the Boston Children's Hospital gives the following as one of the reasons/advantages for doing a double red cell donation rather than the simpler procedure (emphasis added):

Lower total blood volume loss because you receive plasma/platelet and saline solution back. You leave more hydrated!"

If you leave the donation center with more hydrated than when you entered (because of most of the plasma water returned to you, in addition to an extra saline solution), then is it still necessary to hydrate so much (the 16 ounces of water suggested above) before doing a double red cell donation? There's an answer to this, but it takes deeper research to find the actual reason (indeed your own blood cell clinic didn't know when you asked them, and all the above articles don't give any additional reasons for hydration which still apply in the double red cell donation case).

Why you should still be well-hydrated even for a double red cell donation

One may have to read through more of the search results to find this, but the above reasons for hydration aren't the only ones given, particularly the Upstate Medical University says (emphasis mine):

"Donating blood isn't hard to do, but it will go quicker if you have a lot of fluids in your system. If you are more hydrated, your veins will be easier to find and your blood will flow more easily. The American Red Cross suggests drinking an extra 16 ounces of water before and after your donation —even if you don‘t feel thirsty."

Likewise, Canada Plasma Resources says:

"Since plasma is 90% water, your level of hydration while donating plasma will impact the viability of your donation. Drinking enough water directly affects how full your vein is and how your plasma is separated during the plasmapheresis process. Ideally, you should drink six to eight cups of water on the day of your donation!"

Conclusion based on everything above

By being well hydrated you:

  • make your veins easier to find,
  • make your veins more "full",
  • make the blood flow more easily,
  • make the plasma separation easier during the plasmapheresis process,
  • make the overall process quicker and easier for yourself and the staff

During a double red cell donation, it is true that the dehydration-like symptoms that would typically concern you after a whole blood donation, might not be as much of a concern since it was said in a quote above that you leave the clinic more hydrated than before. So the need to hydrate yourself after the process might not be as convincing, but all the reasons for hydrating before the process still apply.

The last link I gave contained some useful tips for how to recognize dehydration if you do somehow end up not being well enough hydrated after your plasma and saline solution are returned to you:

  • Feeling thirsty
  • Feeling dizzy or lightheaded
  • Fatigue
  • Confusion
  • Dry mouth, lips, or eyes
  • Less frequent urination and/or dark coloured urine

Importantly though, dizziness, lightheadedness, confusion and fatigue can be symptoms of over-hydration too, and since it's been said in a quote above that you leave the double red cell donation procedure more hydrated than when you first came, you should also be careful not to over-hydrate yourself.


You still need to hydrate yourself before the procedure. The reasons for this are independent of whether you're doing a double red cell donation or a whole blood donation, but in the double red cell case, you may not need to hydrate as much afterwards (and even overhydration can become a concern since you can leave more hydrated than you came). It's good to know the symptoms of dehydration as well as for overhydration so that you can adjust your water intake accordingly.

Further reading

Article: "Why Should You Stay Hydrated Before Donating Blood?"

  • 1
    Thank you. That does help. And will hopefully help others. Jan 24, 2022 at 13:49

According to the Stanford Blood Center and the American Society for Apharesis, you should increase your intake of fluids, calcium, and iron at least two days before your platelet donation appointment – this will help prevent negative donation reactions.

  • I just realized that your answer is for platelet donation. I do RBC apharesis. Jan 17, 2022 at 20:07

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