Plasma Donation

[Damasta]

So I actually did this calculation for my little sister, but I thought I'd share it here since it's somewhat relevant.

The average adult has 4.7 to 5.0 Liters of blood. (source). I'll assume 5.0 Liters for ease of calculation.

The average adult has 20 to 30 trillion red blood cells (source). For my purposes, I'll use the high end, 30 trillion red blood cells. That leaves us with approximately 6 trillion red blood cells per Liter.

A typical blood donation removes 0.5 Liters of blood (source), which constitutes a loss of 3 trillion red blood cells.

The average adult produces 2 million new red blood cells per second (source).

At that rate it would take you 2.5 million seconds/42 thousand minutes/695 hours/29 days (I rounded up in the latter three cases) to replenish your lost blood. But that doesn't take into account the cells that naturally die during that time and need to be replaced. But it gives you a rough estimate: a minimum of one month to replenish your red blood cell supply after a typical donation.

That leads me to conclude that 6 months before donating plasma is excessive. In the U.S. they typically make you wait 2 months/56 days before making another whole-blood donation (source).

[Darth Fedora]

Interestingly, if your blood is suddenly too low in RBCs (from donating blood, or hemorrhage, or being put in an oxygen-poor atmosphere), your body will actually up-regulate RBC production. So it could very well take much less than a month to replenish the lost blood.