Question

In preparation for a scheduled surgery, a patient visits the hospital lab for a blood draw. The technician collects a blood sample and performs a test to determine its type. She places a sample of the patient's blood in two wells. To the first well she adds anti-A antibody. To the second she adds anti-B antibody. Both samples visibly agglutinate. Has the technician made an error, or is this a normal response? If normal, what blood type does this indicate?

Short answer

Answer: The technician did not make an error, and the observed agglutination is a normal response for a patient with blood type AB.

Step-by-step solution

Understand blood types and antibodies

There are four main blood types: A, B, AB, and O. Each blood type has specific antigens and antibodies. Blood type A has antigen A and antibody anti-B, blood type B has antigen B and antibody anti-A, blood type AB has both antigens (A and B) and no antibodies, and blood type O has no antigens but both antibodies (anti-A and anti-B).

Analyze the result of the blood test

The technician added anti-A antibody to the first well and anti-B antibody to the second well. After adding these antibodies, both samples visibly agglutinated. Agglutination refers to the clumping of red blood cells due to the binding of antibodies to antigens present on the surface of the cells. The presence of agglutination indicates the presence of the corresponding antigens in the patient's blood.

Determine if the results are normal or indicate an error

Since both samples agglutinated when the anti-A and anti-B antibodies were added, it means that the patient's blood sample contains both antigen A and antigen B. This is a normal response for blood type AB.

Identify the patient's blood type

Based on the observed agglutination after adding anti-A and anti-B antibodies, the patient's blood type is AB, as it is the only blood type that has both antigen A and antigen B on the red blood cells. There is no indication of error in the blood typing procedure. In conclusion, the technician did not make an error, and the observed agglutination is a normal response for a patient with blood type AB.

Key concepts

Blood Types

Understanding blood types is crucial, as they determine compatibility for transfusions, organ transplants, and maternal-fetal health. Blood is classified into different groups based on the presence of specific molecules called antigens on the surface of red blood cells. The main blood types in the ABO system are A, B, AB, and O.

Each blood type is determined by the combination of antigens present. For example, blood type A has A antigens, type B has B antigens, type AB has both A and B antigens, and type O has neither. This system is pivotal for ensuring safe blood transfusions since receiving incompatible blood can lead to serious and potentially fatal reactions.

Antigens and Antibodies

Antigens are substances that the body recognizes as foreign and that can trigger an immune response. In the context of blood types, antigens are specific proteins or carbohydrates on the surface of red blood cells.

Antibodies are proteins made by the immune system to neutralize antigens. Each blood type has corresponding antibodies that will attack foreign blood types. For example, if you have blood type A, you possess B antibodies, which will target B antigens. This mechanism is the body's natural defense against unknown cells which could be potentially harmful.

Agglutination Reaction

The agglutination reaction is a key concept to understand when typing blood. This reaction occurs when antibodies bind to their corresponding antigens on the surface of red blood cells, causing the cells to clump together, or agglutinate. This clumping can be directly observed under a microscope or visually when a sample is mixed with antibodies in a test.

During a blood typing test, the presence of agglutination indicates which antigens are on the red cells' surface. For instance, if agglutination occurs when anti-A antibody is added to a blood sample, it signifies that A antigens are present, suggesting a blood type of A or AB.

ABO Blood Group System

The ABO blood group system is the primary blood classification system used to determine blood types in humans. This system categorizes blood based on the presence or absence of antigenic substances on the surface of red blood cells.

The breakdown is as follows: blood type A has the A antigen, B has the B antigen, AB has both A and B antigens, and O lacks both. Understanding this system is fundamental for medical procedures like transfusions. Knowledge about the ABO system, coupled with Rh factor determination, ensures compatibility and prevents potentially life-threatening immune responses.