@JPB,
This is what I was looking for...
There are large differences in donation policies and practices in different parts of the world.
Quote:According to traditional Chinese medicine (TCM), donating 200-400ml of blood once every two years - not more frequently - is not a problem and may even enhance the body's ability to produce more blood.
In the West, whole blood can be donated every eight weeks, but regular donors usually give two or three times a year. Some people donate out of charitable impulse: No preparation is required - just good health. Afterward, donors are usually given some juice and cookies for energy, observed for 20 minutes or so for possible dizziness - and then they're on their way.
Because donating is a big deal in China, two weeks' advance preparation is ideal before donating - lots of rest, no vigorous sports and lots of nourishing food. That's why people are notified two weeks in advance of their donation appointments.
And after donating, two weeks' rest is recommended - no work and more nourishing, energy-reinforcing food to build up the blood and energy (recipes below). And still many people are reluctant to donate.
According to Western medicine theory, a 200ml donation of blood only represents five to 10 percent of the total in a healthy adult. The blood loss is quickly made up and a healthy adult can recover completely in 10 days after donation.
As TCM attaches great importance to blood as the carrier of nutrition and source of energy, it also emphasizes the need to help the blood regenerate quickly.
Source
I've also seen many references to donation volume of 200ml and >300ml. I recall from previous reading that some countries collect half-units from smaller people (women, and smaller men) and full units from others, based on weight and health.