BLOOD TYPES
Blood is covered with proteins. Some of those proteins are antigenic. Your blood type is determined by the patterns of these antigens on your blood cells. There are over 30 different blood types, each one corresponding to a family of antigens. But only 2 of these are both common and clinically significant.
ABO Antigens. There are two different antigens here. Antigen A and Antigen B. They arise from an interaction with the gut flora when we’re babies. So if you have Antigen A in your blood, you’ll see Antigen B in your gut and make antibodies against Antigen B. ABO induces an IgM response. IgM can cause severe intravascular hemolytic anemia. ABO Antigens somehow spread in an autosomal dominant pattern.
Type A - If your RBCs have Antigen A, then you have antibodies for Antigen B. They can’t receive Type B or Type AB blood
Type B - If your RBCs have Antigen B, then you have antibodies for Antigen A. They can’t receive Type A or Type AB blood
Type AB - If your RBCs have both A and B, then you have antibodies for neither. They can receive all blood. Universal recipient!
Type O - If your RBCs have neither A or B, then you have antibodies for both. They can’t receive Type A, Type B or Type AB blood. Universal donor!
Rh Antigens. There are 50 different Rh antigens, but the most important is Antigen D. It induces an IgG response, and IgG causes extravascular hemolysis. Rh D is passed down from parent to child in an autosomal dominant pattern. There’s a random pregnancy tidbit that you have to know here. When the placenta falls out during delivery, the chorionic villi shear causing mom and baby’s blood to mix for the first and last time.
Rh Positive - If you have the Rh D Antigen, then you won’t have antibodies for the Rh D Antigen. 85% of the population is Rh+. No problems here.
Rh Negative - If you lack the Rh D Antigen, you WON’T have antibodies for the Rh D Antigen. But if you become exposed to the Rh D Antigen (an Rh- mother delivers her first Rh+ baby), then you start to develop the antibodies. When the mom delivers her second Rh+ baby, the child will be flooded with antibodies in utero, and may suffer from Hydrops Fetalis. Prevent this by giving RhoGAM, a special antibody for Rh D Antigen that does not cross the placenta, during the 28th week of the first delivery. RhoGAM sops up any baby blood that spills into mom. The baby is safe because it doesn’t cross the placenta.
Type - a test for the ABO blood type
Screen - a test for Rh and a handful of other important blood types. Performed by adding synthetic RBCs (covered in the most high-yield antigens) to the donor’s blood.
Cross - the ultimate test. Donor and recipient blood are mixed. If they agglutinate or hemolyse, then they are incompatible.
TRANSFUSIONS
For historical and practical reasons, you rarely give whole blood (some components degrade faster than others, others like certain storage conditions, it’s quicker to administer, it allows for more sophisticated usage). The only instance when you would give complete blood is massive hemorrhage. Blood is broken down into different components
TRANSFUSION REACTIONS
The first step in any suspected transfusion reaction is to stop the administration of the blood product!
Allergic Reaction - patients with an IgA deficiency have unusually high rates of allergic reactions following transfusions. If their transfusion contains IgA, the foreign IgA can ignite a classic type 1 hypersensitivity reaction. This reaction occurs within seconds -- the fastest transfusion reaction. Give benadryl, steroids and/or epinephrine.
Acute Hemolytic Reaction - mismatched ABO/Rh transfusion (type II hypersensitivity) leads to fever, flank pain, dark urine and perhaps shock. Many patients will only have fever or chills. Occurs within minutes, typically around 15 minutes. The Coombs test will be positive. Administering as little as 10mL of mis-matched blood can cause this reaction. The administered RBCs are swiftly killed by the complement system, causing a flood of cytokines and NO that can lead to a fever and chock. The kidneys are often damaged, and the reasons why are a little complicated.
Febrile Nonhemolytic Transfusion Reaction - patient gets hot and flushed because of cytokines that have accumulated in the storage bag. Harmless and self-limiting. Occurs within minutes.
Transfusion Related Acute Lung Injury (TRALI) - neutrophils like to chill in the lung. In fact, about 30% of your neutrophils are in your lungs at any given time! Sometimes they get irritated by donor blood, and create an inflammatory storm in the lungs. This leads to pulmonary edema and respiratory symptoms. Occurs within the first few hours, typically around 6 hours. This is one of the deadliest post-transfusion complications! The patient’s oxygen saturation should drop below 90%, and their chest x-ray should show bilateral infiltrates. Fever and shock are also common.
Transfusion Associated Circulatory Overload (TACO) - when administered blood products cause the patient to become volume overloaded. Seen in (a) patients who are already predisposed to fluid overload (CHF) and (b) in massive transfusion protocols where several liters of blood products are administered. There is a lot of clinical overlap between TACO and CHF. Treated with diuretics.
Graft vs. Host Disease - all blood products contain trace amounts of white blood cells. Transfusion labs go to great efforts to eliminate these pesky leukocytes, but it’s impossible to get rid of them completely. These white blood cells will occasionally attack the body that they are transfused into. If the foreign leukocytes have a certain HLA pattern, then the host body will be unable to stop the pillaging white blood cells! Symptoms, which appear several weeks later, consist of rashes, vomiting, diarrhea and mucosal sloughing. About a third of patients die right away, and the survivors often suffer from chronic disease.
Delayed Hemolytic Transfusion Reaction - patient gets mild fever/hyperbilirubinemia 2-3 days later, usually do to one of the non-D Rh antigens (the body doesn’t keep huge circulating numbers of Rh antibodies, so it takes 2-3 days for the body to ramp up antibody production)
Hypocalcemia is common following transfusion because blood products are stored with citrate. Citrate prevents blood from clotting inside the bag. It also will bind to calcium. That is why receiving transfused blood products can lower your calcium.
