Blood Donation: Who Can Donate, What Actually Happens, and the Myths
Blood cannot be manufactured. Every unit transfused came from a person who turned up and gave one. Most eligible adults never do, usually because of beliefs about the process that are not accurate.
Basic eligibility
Criteria vary by country, but typically:
- Age roughly 18 to 65, with some services accepting 16 to 17 with consent and extending the upper limit for regular donors
- Weight at least 50 kg
- Haemoglobin above a threshold, commonly around 12.5 g/dL for women and 13.0 g/dL for men
- Feeling well on the day
- Normal blood pressure and pulse on screening
- No fever or active infection
Interval between whole blood donations is usually around 12 weeks for men and 16 weeks for women, though this differs between countries. Platelet donation by apheresis can be done much more frequently.
Common temporary deferrals
- Recent tattoo or piercing, commonly 3 to 6 months depending on local rules
- Recent dental work, usually days to weeks
- Antibiotics or active infection
- Pregnancy, and typically 6 to 12 months after delivery
- Breastfeeding, depending on local policy
- Recent surgery
- Recent travel to a malaria-endemic area
- Recent vaccinations, with varying intervals
- Low haemoglobin on the day
Common permanent deferrals
- HIV, hepatitis B or hepatitis C infection
- Certain cancers
- Some heart conditions
- Having received human pituitary-derived growth hormone
- Injecting drug use
These exist to protect the recipient, who is often immunocompromised or critically ill, and in some cases to protect the donor.
Deferral rules around sexual history have changed substantially in many countries, moving from blanket group-based exclusions to individual risk assessment. If you were deferred years ago under old rules, it is worth checking current policy.
What actually happens
The whole visit takes around 45 to 60 minutes. The donation itself takes 8 to 12 minutes.
- Registration and identification
- A confidential health questionnaire
- A brief check: haemoglobin by fingerprick, blood pressure, pulse, temperature
- The donation, lying or reclining, with a needle in the arm vein
- Refreshments and 10 to 15 minutes of observation
A standard whole blood donation is around 450 mL, roughly 8 to 10 per cent of your blood volume.
What the body replaces, and how fast
- Plasma volume: within 24 to 48 hours, faster with good hydration
- Platelets and white cells: within days
- Red blood cells: 4 to 6 weeks
- Iron stores: this is the slow one, taking months, and it is the reason for the minimum interval between donations
Keep reading
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Preparing your ad…
Regular donors, particularly menstruating women, can develop low ferritin even with normal haemoglobin. If you donate frequently and feel unusually tired, ask for a ferritin test rather than only a haemoglobin check.
Preparing
- Eat a proper meal within a few hours beforehand, and do not donate on an empty stomach
- Drink extra water in the hours before, which measurably reduces faintness
- Avoid fatty food immediately before, since lipaemic plasma can make a unit unusable
- Sleep adequately the night before
- Avoid alcohol the night before
- Wear sleeves that roll up easily
- Bring identification
Afterwards
- Keep the dressing on for several hours
- Drink extra fluid for the rest of the day
- Avoid heavy lifting or vigorous exercise with that arm for about 12 hours
- Avoid alcohol for several hours
- Do not smoke for at least 30 minutes, which reduces faintness
- If you feel light-headed, sit or lie down and raise your legs
- Eat normally; there is no special diet required
Bruising at the site is common and harmless. Persistent arm pain, numbness or tingling should be reported to the blood service.
The myths
“It will make me weak.” Most people feel entirely normal. Temporary light-headedness happens in a small minority and settles quickly.
“I will gain or lose weight.” Donating does not meaningfully change weight. The commonly cited figure about calories burned is irrelevant to body weight.
“The needle will give me an infection.” Everything that touches you is sterile, single-use and discarded. It is not possible to catch any infection by donating blood.
“My blood type is common so it is not needed.” Common types are needed most, because most recipients have them. O negative is in constant demand because it can be given in emergencies before typing, and O positive is the most transfused type overall.
“I take medication, so I cannot donate.” Many common medicines, including most blood pressure drugs, do not disqualify you. Ask rather than assume.
“I am vegetarian, so my iron is too low.” Many vegetarians donate without difficulty. The haemoglobin check on the day decides it.
What a donation is used for
A single unit is usually separated into components, so one donation can help more than one person:
- Red cells: surgery, trauma, anaemia, childbirth complications
- Platelets: cancer treatment, leukaemia, bleeding disorders. Short shelf life, often only about five to seven days, which is why platelet donors are in constant demand
- Plasma: clotting factor replacement, burns, and manufacture of plasma-derived medicines
Red cells typically last around 35 to 42 days in storage, which is why supply depends on continuous donation rather than stockpiling.
Other ways to donate
Apheresis separates out a specific component and returns the rest. Platelet apheresis takes longer, around 1.5 to 2 hours, but can be done far more frequently and yields several times the platelets of a whole blood donation.
Directed donation for a specific patient is permitted in some systems.
Autologous donation, banking your own blood before planned surgery, is used in selected cases.
The short version
If you are healthy, over 50 kg, and not in a deferral category, you can almost certainly donate, and the needle is in your arm for about ten minutes. You cannot catch anything from donating, common blood types are the most needed, and the only part of you that takes months to recover is your iron stores, which is exactly why the waiting interval exists.