Blood donation centers turn away a surprising number of willing donors. In the U.S., you must be at least 17 years old (16 with parental consent) and weigh at least 110 pounds just to walk through the door. But beyond those basics, dozens of less obvious factors can disqualify you, some temporarily and some permanently. Here’s a breakdown of the most common reasons people get deferred.
Low Iron or Hemoglobin Levels
Every donor gets a quick finger-prick test before giving blood. If your hemoglobin is too low, you’ll be sent home. The minimum threshold is generally 12.0 g/dL for women and 13.0 g/dL for men. These cutoffs exist to protect you: donating a pint of blood when you’re already low on iron can tip you into anemia, causing fatigue, dizziness, and weakness.
This is one of the most common reasons people get deferred, especially women who menstruate. If low hemoglobin is the reason you were turned away, eating iron-rich foods like red meat, spinach, and fortified cereals in the weeks before your next attempt can help. You can usually try again after a short waiting period.
Medications That Affect Your Blood
Several common medications will temporarily disqualify you, not because they’re dangerous to you, but because traces in your blood could harm the person receiving it or because they affect how blood clots and functions.
- Blood thinners: Most require a 7-day wait after your last dose. This includes common prescriptions for preventing blood clots and strokes.
- Antiplatelet drugs (taken to prevent heart attack or stroke): Wait times range from 2 days to 1 month depending on the specific drug.
- Isotretinoin (severe acne treatment, formerly sold as Accutane): 1-month deferral. This medication causes birth defects, so it cannot be present in donated blood.
- Finasteride (used for hair loss or prostate symptoms): 6-month deferral for the same reason.
- Dutasteride (prostate medication): 6-month deferral.
Standard over-the-counter medications like ibuprofen, acetaminophen, and most antibiotics typically don’t disqualify you. If you’re unsure about a specific prescription, calling the donation center ahead of time saves a wasted trip.
Recent Tattoos or Piercings
If your tattoo was done at a licensed, inspected parlor using sterile technique, you can donate immediately in most cases. The same applies to ear and body piercings done with sterile, single-use equipment like a piercing gun. The concern isn’t the tattoo itself; it’s the small risk of bloodborne infection from non-sterile needles.
You will need to wait 3 months if your tattoo was self-applied, done at an unlicensed shop, applied outside the country, or done in a state that doesn’t regulate tattoo parlors. The same 3-month rule applies to piercings performed without sterile single-use equipment.
Travel to Certain Countries
Traveling to areas where malaria is common triggers a waiting period. Most travelers to a malaria-risk region must wait 3 months after returning before donating. If you previously lived in one of those areas, the deferral stretches to 3 years. And if you’ve actually been diagnosed with malaria, you’ll need to wait 3 years after completing treatment while remaining symptom-free.
One piece of good news for people who lived in or traveled through the U.K. or parts of Europe during the mad cow disease era: the FDA has removed the lifetime ban that previously applied. People who were deferred for spending time in the U.K. between 1980 and 1996, or in France and Ireland between 1980 and 2001, can now requalify as long as they meet all other eligibility requirements.
Infections and Illnesses
Certain infections result in temporary deferrals, while others are more complicated. If you’ve had syphilis or gonorrhea, you must wait at least 3 months after completing treatment. A positive syphilis screening test at the donation center will defer you indefinitely, though you can be reentered into the donor pool after successful treatment and a 3-month wait, or if follow-up testing shows the original result was a false positive.
HIV and hepatitis B or C result in permanent deferral. These viruses can survive in donated blood and pose serious risks to recipients, even with modern screening. If you’re feeling sick on the day of your appointment with a cold, flu, or other acute illness, you’ll generally be asked to come back when you’re feeling better.
The Updated HIV Risk Screening
For decades, all men who had sex with men were subject to blanket deferrals, first a lifetime ban, later reduced to 12 months and then 3 months. In May 2023, the FDA replaced this policy with an individual risk-based questionnaire. Instead of asking about sexual orientation, donation centers now ask all donors the same set of questions about specific recent sexual behaviors that carry higher risk for HIV transmission.
This means sexual orientation alone no longer disqualifies anyone. The screening focuses on individual behaviors like having a new sexual partner in the past 3 months combined with anal sex, regardless of gender. The change brought U.S. policy closer to the approaches already used in the U.K. and Canada.
Chronic Conditions Like Diabetes and High Blood Pressure
Having diabetes does not automatically disqualify you. If your condition is well controlled through diet, oral medication, or insulin, you can donate. The one exception is insulin derived from beef, which results in a permanent deferral (though this type of insulin is rarely used today).
High blood pressure is also manageable. Your blood pressure gets checked at the donation site, and you’ll be cleared as long as it reads below 180/100 at the time of your visit. Medications for blood pressure don’t disqualify you. Essentially, if your chronic condition is stable and you feel well on donation day, you’re likely eligible.
Pregnancy and Postpartum
You cannot donate blood while pregnant. After delivery, the recommended waiting period matches the length of your pregnancy, so about 9 months for a full-term birth. If you’re breastfeeding, the WHO recommends waiting until at least 3 months after your baby is mostly weaned to solids or formula. Your body needs that time to rebuild its own blood volume and iron stores.
These guidelines also apply after a miscarriage or termination, with the deferral period scaled to however far along the pregnancy was.
Temporary vs. Permanent Deferrals
Most reasons for being turned away are temporary. Low iron, recent travel, tattoos, medications, pregnancy, and many infections all come with a waiting period after which you can try again. Permanent deferrals are less common and typically involve conditions where the risk to blood recipients can’t be eliminated through waiting or testing, such as HIV, hepatitis B or C, or certain prion disease exposures.
If you were deferred and aren’t sure why, or don’t remember the details, your donation center can pull up your record and tell you exactly what triggered it and when you’ll be eligible again. Many people who assume they’re permanently banned actually just need to wait a few weeks or months.