Giving blood is a potentially life saving procedure that almost everyone can take part in. However, there is a small segment of the population for whom giving blood may actually be harmful, even if only temporarily. This may happen for a myriad of reasons but the two main reasons are that the removal of the donated blood could be harmful to the donor, or the blood donated could be harmful to the recipient.

Often, people trying to give blood are turned away after the ‘pin prick’ part of the experience and told “you are anemic.” Blood donors are required to have a hemoglobin level of at least 12.5 g/dL or hematocrit of 38% in order to donate blood. This is to ensure that donors have an adequate number of red blood cells (RBCs) for donation as well as adequate iron stores for the creation of more blood cells following donation. Being deferred from donation due to a low hematocrit during screening does not always mean the patient is anemic or has a medical problem. For example, male donors with a hematocrit below the acceptable 38% are considered anemic, but non-anemic women within the normal hematocrit range of 36-37% are not able to donate blood. Although this practice turns away non-anemic women from donating blood, it reduces the chance of depleting their iron stores and potentially causing anemia following donation. Men are allowed to donate when slightly anemic because it is much easier for them to replace the iron lost during donation.

Another reason people are not able to donate is that not enough time has passed since the last time they gave blood. Blood is used in the body to provide a medium to transport vital nutrients such as oxygen and glucose (sugar) for the cells to function appropriately. Removal of too much blood, whether at one sitting or too soon after a previous donation, means that the donor’s body will not have enough blood to provide the cells with the nutrients they need, and this can lead to some level of bodily dysfunction. It is safe to attempt to donate blood every eight weeks.

Donors must weigh at least 110 lbs to be eligible for blood donation. This regulation is for their own safety as blood volume is determined by body weight and height. Individuals with low blood volumes may not tolerate the removal of the required volume of blood given with whole blood donation. There is no upper weight limit as long as the donor’s weight is not higher than the weight limit of the donor bed/lounge they are using.

Generally donors must complete an extensive questionnaire prior to giving blood. If the potential donor indicates they have a history of bleeding problems, they will be asked additional questions. If their blood does not clot normally, they should not donate as they may experience excessive bleeding where the needle was placed. For the same reason, if the donor is taking any "blood thinners" (such as coumadin or heparin) they should not donate. If they are on aspirin, it is safe to donate whole blood. However, they must be off of aspirin for at least 48 hours in order to donate platelets by apheresis.

A few other reasons that donors may be turned away and prevented from giving blood include extremely high or low blood pressure. Donors with high blood pressure will be accepted so long as their blood pressure is below 180 systolic (first number) and below 100 diastolic (second number) at the time of donation. Medications for high blood pressure do not disqualify you from donating. If they have low blood pressure will be accepted so long as they feel well when they come to donate, and their blood pressure is at least 80/50 (systolic/diastolic).

Another reason someone would be deemed ineligible to donate would be that the donor has sickle cell disease. Those with sickle cell trait can safely donate blood.

Lives are saved as a result of blood donation, so even if someone has been turned away before, it is well worth trying to donate again.