Abstracted from the Red Cross official page.

Blood Donation Eligibility Guidelines

General
To give blood, you must be healthy, at least 17 years old, and weigh at least 110 pounds.

Specific

AIDS
Do not give blood to get an AIDS test. Please see your own doctor or local health department to get tested. We are required to report all positive HIV results to public health officials.

If you have any reason to believe you have AIDS, do not donate blood. You risk harming a vulnerable patient who needs blood transfusions. With new, advanced tests, the risk of transmitting HIV through a blood transfusion is 1 in 1.5 million.

However, before blood is drawn, we must ensure that a donor does not display the high risk behaviors associated with certain infectious diseases. Do not give blood if you are at risk for getting and spreading the AIDS virus. According to the Food and Drug Administration, you are at risk if:

AIDS Exposure

Allergy

Asthma

Blood Pressure

Blood Transfusion

Cancer

Cold, Flu or Sore Throat

Creutzfeldt-Jakob Disease (CJD)

Dental

Diabetes

Epilepsy

Heart Disease/Surgery

Hemoglobin

Hepatitis/Unexplained Jaundice

Hepatitis Exposure

Immunization/Vaccination

Infectious Mononucleosis

Malaria

Medications

Organ/Tissue Transplants

Pregnancy

Serious Illness

Sickle Cell

Skin Disease and Rash

Surgery

Syphilis/Gonorrhea

Travel Outside of U.S.