Dozens of factors can disqualify you from donating blood, ranging from low iron levels to recent tattoos to certain medications. Some are permanent, others temporary. The rules exist to protect both you and the person receiving the blood, and many of the most common disqualifiers are things you can address and come back to donate later.
Age, Weight, and Basic Health
You must be at least 17 years old to donate whole blood, or 16 with parental consent. You also need to weigh at least 110 pounds. These thresholds exist because removing a standard unit of blood from a smaller body puts too much strain on your system.
On the day you show up, staff will check your blood pressure, temperature, and pulse. Your systolic blood pressure needs to fall between 90 and 180, and diastolic between 50 and 100. Your pulse has to be regular and between 50 and 100 beats per minute. If you’re outside those ranges, you’ll typically be turned away for the day, though a physician can sometimes clear you remotely.
You’ll also get a finger prick to check your hemoglobin, the protein in red blood cells that carries oxygen. Men need a level of at least 13.0 g/dL. Women need at least 12.5 g/dL, though some collection centers can accept women down to 12.0 g/dL with extra safety steps. Low hemoglobin is one of the most common reasons people get deferred at the donation center, and it often traces back to iron deficiency.
How Iron Levels Affect Eligibility
Every time you donate whole blood, you lose a significant amount of iron. In the U.S. and Canada, men can donate roughly every 56 days, or about seven times a year. Women are generally encouraged to donate less frequently because of menstrual iron losses. European countries are more conservative: the U.K. and Hong Kong limit men to four donations per year and women to three.
If you donate frequently and your hemoglobin or stored iron drops too low, the recommended course is to start taking iron supplements and take a break from donating until your levels recover. This is temporary, not permanent.
Medications That Disqualify You
Most common medications, including blood pressure drugs, antidepressants, and birth control, won’t prevent you from donating. The ones that do tend to fall into a few categories.
- Isotretinoin (severe acne treatment): one-month wait after your last dose.
- Finasteride and dutasteride (hair loss or prostate drugs): six-month wait.
- Blood thinners: wait times vary. Some require just seven days, while others require a longer deferral. The concern isn’t about your safety but about the effect on the blood product itself.
- Anti-platelet drugs: wait times range from two to 14 days depending on the specific drug.
- Antibiotics: you generally can’t donate while actively taking them, since they signal an ongoing infection.
The key detail: these deferrals are measured from your last dose, not from when you started the medication. Once the waiting period passes and you feel well, you’re eligible again.
Infections and Chronic Conditions
A few infections permanently disqualify you. If you’ve ever tested positive for HIV, you cannot donate, regardless of treatment. Even when antiviral therapy makes the virus undetectable in the bloodstream, the “undetectable equals untransmittable” principle that applies to sexual transmission does not apply to blood transfusions. The virus can still be present in donated blood at levels that put recipients at risk.
Hepatitis B and hepatitis C also result in permanent deferral. Both viruses can persist in the blood long after symptoms resolve, and the consequences for a transfusion recipient with a compromised immune system are severe.
If you’re currently sick with a cold, flu, or other acute illness, you’ll need to wait until you’ve recovered. This is a short-term deferral, not a permanent one.
Cancer History
A cancer diagnosis doesn’t necessarily disqualify you forever. Recent guideline changes have shortened waiting periods significantly. If you completed chemotherapy or radiation, you now typically need to wait just one year rather than the previous five. If your treatment was surgery alone, the wait can be as short as two weeks once your doctor clears you. Certain cancers and ongoing cancer medications still result in longer or permanent deferrals, but many survivors are now eligible sooner than they might expect.
Tattoos and Piercings
In most states, a tattoo done at a licensed, state-regulated facility with sterile, single-use needles and ink is fine, and you can donate with no waiting period. The same applies to piercings done with disposable, single-use equipment. The concern behind these rules is hepatitis transmission.
If you got your tattoo in a state that doesn’t regulate tattoo shops, or if there’s any question about whether the instruments were single-use, you’ll need to wait three months. The same three-month deferral applies to piercings done with a reusable piercing gun.
Sexual Activity and Risk Assessment
Blood donation screening in the U.S. has moved toward individual risk-based assessment rather than blanket deferrals tied to gender or sexual orientation. The older policy that deferred men who have sex with men for 12 months was first reduced to three months in 2020, and the FDA has since been piloting questionnaires that focus on specific risk behaviors regardless of who you are.
Studies in countries that adopted individual risk-based screening found no increase in HIV-positive donations. The goal is to identify higher-risk sexual behaviors, like having a new sexual partner or multiple partners in a recent window, rather than categorically excluding groups of people.
Travel Restrictions
For years, anyone who spent significant time in the U.K. during the 1980s and 1990s was permanently barred from donating due to concerns about mad cow disease (variant Creutzfeldt-Jakob disease). The FDA has since removed those geographic deferrals. Time spent in the U.K. from 1980 to 1996, or in France and Ireland from 1980 to 2001, no longer disqualifies you. People who received blood transfusions in those countries during those periods are also no longer deferred.
Travel to areas with active malaria transmission can still trigger a temporary deferral, typically lasting several months after you return.
Pregnancy and Breastfeeding
You cannot donate blood while pregnant. After delivery, the World Health Organization recommends waiting at least as many months as the pregnancy lasted, which means roughly nine months for a full-term pregnancy. If you’re breastfeeding, the deferral extends until about three months after your baby is getting most nutrition from solid food or formula rather than breast milk. These timelines let your body rebuild its own blood volume and iron stores.
Vaccines
Most vaccines don’t require any waiting period at all. If you received an mRNA or inactivated COVID-19 vaccine, a flu shot, or other non-live vaccines, you can donate immediately as long as you feel well. Live attenuated vaccines, like MMR (measles, mumps, rubella) or certain shingles vaccines, require a wait of 14 to 28 days depending on the specific vaccine and the blood collection organization’s policy.
Donation Frequency
Even if you’re perfectly healthy, you can be turned away simply for donating too recently. For whole blood, the minimum interval is 56 days (eight weeks) in the U.S. Platelet donations can be made more frequently, but whole blood requires that gap to let your body regenerate red blood cells and replenish iron. If you show up before that window has passed, you’ll be asked to come back later.