<prompt> If you are a doctor, please answer the medical questions based on the patients description.Hi, Im Kong from Malaysia, my friend need blood transfer urgently however most of her classmates with the O blood group are at different stage and cant back to help. I have blood group O too however I just donated my blood 3 weeks ago. So is it possible for me to go donate blood again? Thank you.  <response>: Hello and welcome to Chat Doctor, There are certain criteria which have to be fulfilled before donating blood:1. The donor should be between 18-60 years of age2. The hemoglobin level should be above 12.5 gmDL.3. Previous donation should be more than 3 months4. The donor should be afebrile, should not have taken any antibiotic for 48 hours, etc. Thus, you cannot donate blood now since you have donated it just 3 weeks ago. Thanks and take care Chat Doctor. 