Blood donation supply

Why does the blood supply run short when almost everyone says donating is worth doing?

Ask people whether donating blood is a good thing and you get near-unanimous agreement. It is safe, it is quick, it is free to give, and everyone can picture the person at the other end of it. There is no organised opposition and no serious controversy.

And yet blood services spend their year issuing appeals, and shortages are routine rather than exceptional. In the United States, roughly three in a hundred age-eligible people actually donate in a given year, against something like sixty in a hundred who could. So the gap is not between opponents and supporters. It is between people who approve of donating and the very same people not doing it. What sort of problem produces that shape?

Begin with the shape of the decision as one person faces it. What does your donation cost you? An hour, a needle, some inconvenience, and a small chance of feeling unwell. What does it gain you? Essentially nothing material — and here is the important part — because whether or not you donate, if you are ever in an accident the blood will be there for you exactly as it would have been.

Sit with that asymmetry, because it is the whole engine. The benefit of a stocked blood supply is available to everyone regardless of contribution, while the cost falls entirely on the contributor. And no single donation is pivotal: the supply does not visibly fail because you skipped, and does not visibly succeed because you went. So for each individual, at each moment, the rational-seeming move is to approve warmly and stay home. Everybody reasoning that way produces exactly what we observe — overwhelming support and a thin supply.

Now add the feature that makes blood harder than most collective-action problems: you cannot stockpile the solution. Red cells keep for around six weeks in refrigeration, and platelets for only about five days, sometimes seven with extra testing. So the supply is not a reservoir that a good year fills. It is a flow, and it must be regenerated continuously and forever. Notice what that does to the appeal: a system that solved recruitment brilliantly this month would be short again within two months, which is why the asking never stops and why donor fatigue is itself a constraint.

Two consequences follow that are easy to miss. First, holidays and bad weather cut collections while trauma demand does not fall, so the shortages cluster predictably. Second — and this is the counterintuitive one — a disaster generates enormous donation surges that mostly cannot help. The blood that treats today's victims was collected weeks ago; blood donated in response to the news arrives after the need has passed, and after the September 11 attacks a large share of the surge went unused. Motivation, when it finally arrives, arrives at the wrong time.

So how do you solve a collective-action problem? The usual answers are compulsion, payment, or lowering the cost of cooperating. Compulsion is not seriously on the table for bodily donation. What about payment?

This is where the argument gets genuinely interesting, and where I should be careful not to make it sound settled. Richard Titmuss argued in 1970 that paying donors would crowd out altruistic giving and attract worse donors, and his view shaped policy in much of the world. The later evidence is mixed. One field experiment in Sweden found a payment reduced women's willingness to donate but not men's, and that the effect vanished when the payment could be given to charity. Other field experiments on economic incentives at blood drives found donations rose rather than fell. Meanwhile paid plasma collection operates at industrial scale. The most defensible summary is that motivational crowding-out is real in some settings and not universal — and that it is not the main lever anyway.

The main lever, it turns out, is friction. Most non-donors are not withholding; they are willing people who were never asked at a moment they could act. Appointment systems, workplace and campus drives, reminders timed to eligibility returning — these move the number, because they attack the actual binding constraint, which is attention and convenience rather than approval.

The tempting diagnosis is a shortage of public awareness, and the natural remedy is another campaign explaining why blood is needed. But the reasoning above says awareness is not the missing input: approval is already near-universal and shortages persist anyway. A campaign that raises approval from ninety to ninety-two per cent changes very little; a text message the week someone becomes eligible again changes quite a lot.

It also helps to see what makes this problem structurally different from most public goods. Money can be raised in advance and held. Blood cannot — so this is a collective-action problem with a decay term attached, and that term means it can never be permanently solved, only continuously managed. The right measure of a blood service is not how many people it has convinced but how reliably it converts willingness into scheduled appointments, week after week.

One honest note on the numbers. Eligibility criteria change — deferral rules for travel, medication and sexual history have been substantially revised in several countries in recent years — so the eligible fraction is a moving figure, and the three-per-cent participation rate is a widely quoted approximation rather than a precise constant.

• Why plasma, which can be frozen for a year, has a different economics from red cells and a largely paid donor base.
• Whether reciprocity schemes that give donors or their families priority access change the collective-action structure or merely relabel it.
• How patient blood management reduces demand rather than chasing supply.

Every term the collection defines is gathered in the glossary.