Donating blood is one of the simplest and most impactful ways to help save lives. Just one unit of blood can help multiple patients in need—whether it’s a victim of trauma, a child with severe anemia, or someone undergoing major surgery. Blood donation is a noble act, but not everyone can or should donate. While the intention might be good, certain medical conditions, medications, or temporary health issues can make it unsafe—for both the donor and the recipient.

This isn’t about exclusion, but protection. Blood banks and health organizations follow strict screening criteria to ensure that donated blood is as safe and effective as possible. These rules also help protect the donor’s own health during and after the process. So, if you’ve ever been turned away or are unsure whether you're eligible, here’s a closer look at some of the most common medical reasons why a person may be deferred from donating blood.

1. Anaemia or Low Haemoglobin - If your haemoglobin is below the minimum threshold (typically 12.5 g/dL for women and 13.0 g/dL for men), you’ll be temporarily deferred. Donating blood when anaemic can worsen fatigue and weakness and may not provide a viable donation for the recipient.
2. Uncontrolled Hypertension or Heart Conditions - People with high blood pressure that isn’t well-managed, or those with serious heart conditions like arrhythmias, angina, or a history of heart attacks, are often ineligible. Blood donation causes a temporary drop in blood volume, which can strain the heart.
3. Recent Infections or Fever - Having a cold, flu, or any active infection makes you ineligible until you're fully recovered. This ensures you’re healthy enough to donate and that the infection isn’t passed on through your blood.
4. HIV/AIDS - Anyone who has tested positive for HIV, or engages in high-risk behaviours like unprotected sex with multiple partners, is deferred. This is a strict precaution due to the potential risk of transmission, even if the blood initially tests negative.
5. Hepatitis B or C - People who’ve had hepatitis B or C are permanently deferred from donating, as the viruses can remain dormant and undetected in blood despite screening tests.
6. Cancer History - Those currently undergoing cancer treatment are not eligible. Some people with a history of cancer may be allowed to donate if they’ve been cancer-free for a certain number of years, but blood banks assess this on a case-by-case basis.
7. Certain Medications - Some medications, like blood thinners or isotretinoin (used for acne), can affect eligibility. These drugs may impact blood safety or the donor’s ability to recover, requiring temporary or even permanent deferral depending on the drug.
8. Pregnancy and Recent Childbirth - Pregnant women and those who have given birth in the last six months are advised not to donate blood. The body needs time to recover from the blood loss during childbirth and support postpartum healing.
9. Chronic Illnesses - Poorly managed chronic conditions can make donation risky. In cases like kidney failure or unstable diabetes, the donation process may strain already vulnerable systems.

Medical science has come a long way in screening and testing blood, but even the best systems have limitations. That’s why pre-donation screening questions and health assessments are so thorough. If you’re temporarily ineligible, take it as an opportunity to focus on your health and perhaps become eligible later.