Blood typing test is a lab investigation which identifies the person's blood group. This test is done for the following indications:

• If there is a need for blood transfusion, as in accidents or due to blood loss during or after surgery.
• In cases of blood donation.
• Blood typing test can be done as one of the routine preoperative lab investigations.

There are 4 different types of blood which differ according to the antigen attached to the surface of RBCs. Generally, blood types include the following:

• Type A: (A) antigen is attached to RBCs.
• Type B: (B) antigen is attached to RBCs.
• Type AB: (A) & (B) antigens are attached to RBCs.
• Type O: there are no antigens attached to RBCs at all.

Not all blood types are compatible, so blood typing test is done for assessment of compatibility between donor's and recipient's blood. Anyway, the rules of blood donation according to blood types include the following:

• Individuals with blood group (O): they can donate blood to anyone (as their blood doesn't contain antigens), while they only receive blood from individuals with blood group O.
• Individuals with blood group (A): they can donate blood to individuals with blood group A or AB, while they receive blood from individuals with blood group A or O.
• Individuals with blood group (B): they can donate blood to individuals with blood group B or AB, while they receive blood from individuals with blood group B or O.
• Individuals with blood group (AB): they can donate blood to individuals with blood group AB, while they can receive blood from any blood type (as they have both A & B antigens).
• On the other side, according to Rh factor, blood types are further classified into:
• Rh positive: it indicates that blood contains Rh antigens. So individuals with Rh positive can receive Rh positive or Rh negative blood.
• Rh negative: it indicates that blood doesn't contain Rh antigens. So individuals with Rh negative can receive only Rh negative blood.
• In conclusion, according to the above facts; there are 8 blood types (A+, A-, B+, B-, AB+, AB-, O+ and O-).