Blood – Part 4

Bleeding Disorders The most common causes of abnormal bleeding are: Platelet deficiency Known as thrombocytopenia Deficits of some of the clotting factors Might result from impaired liver function or certain genetic disorders

Thrombocytopenia Thrombocytopenia – Results from an insufficient number of circulating platelets. Even normal movements cause spontaneous bleeding from small blood vessels. This is evidenced by many small purplish blotches called petechiae on the skin. Can arise from any condition that suppresses myeloid tissue such as: Bone marrow cancer Radiation Certain drugs

Impaired Liver Function When the liver is unable to synthesize its usual supply of clotting factors, abnormal and often severe bleeding episodes occur. If vitamin K (needed by the liver to produce clotting factors) is deficient, the problem is easily corrected with supplements. When liver function is severely impaired (as in hepatitis and cirrhosis) only whole blood transfusions are helpful.

Hemophilia Hemophilia – The term applies to several different hereditary bleeding disorders that result from a lack of any of the factors needed for clotting. Commonly called “bleeder’s disease.”

Hemophilia: Signs and Symptoms Hemophilias have similar signs and symptoms that begin early in life: Minor tissue trauma results in prolonged bleeding and can be life threatening. Repeated bleeding into joints causes them to become disabled and painful.

Hemophilia: Treatment When a bleeding episode occurs hemophiliacs are given either: A transfusion of fresh plasma Injections of the purified clotting factor they lack Hemophiliacs are completely dependent on these therapies.

Loss of Blood Volume The body can compensate for a loss of blood volume up to a certain limit. Losses of 15-30% lead to pallor and weakness. Losses of over 30% cause severe shock, which can be fatal.

Blood Transfusions Are routinely given to replace substantial blood loss and to treat severe anemia and thrombocytopenia. Blood banks mix the collected blood with an anticoagulant to prevent blood clotting. The treated blood can be stored for about 35 days until needed.

Human Blood Groups People have different blood groups and transfusing incompatible or mismatched blood can be fatal. The plasma membranes of RBCs bear genetically determined proteins (antigens), which identify each person as unique. An antigen is a substance that the body recognizes as foreign. Antigens stimulates the immune system to release antibodies or use other means to mount a defense against it. Most antigens are viruses or bacteria.

Human Blood Groups Each of us tolerates our own antigens. One person’s RBC proteins will be recognized as foreign if transfused into another person with different RBC antigens. Antibodies are “recognizers.” Present in the plasma Attach to RBCs bearing surface antigens different from those on the patient’s (blood recipient’s) RBCs.

Agglutination Binding of the antibodies causes the RBCs to clump, a phenomenon called agglutination. Leads to the clogging of small blood vessels throughout the body. During the next few hours, the foreign RBCs are lysed (ruptured) and their hemoglobin is released into the bloodstream.

Transfusion Reactions Most Devastating Consequence: The freed hemoglobin molecules may block the kidney tubules and cause kidney failure. If kidney shutdown does not occur, then the reaction will probably not be fatal. The transfused blood is unable to deliver the increased oxygen-carrying capacity hoped for. Can cause fever, chills, nausea, and vomiting.

Treatment of Transfusion Reactions Treatment is aimed at preventing kidney damage by: Infusing alkaline fluids to dilute and dissolve the hemoglobin Diuretics to flush it out of the body in urine

RBC Antigens There are over 30 RBC antigens in humans, allowing each person’s blood cells to be classified into different blood groups. However, it is the antigens of the ABO and Rh blood groups that cause the most vigorous transfusion reactions.

ABO Blood Groups ABO Blood Groups – Based on which of two antigens, type A or type B, the person inherits. Type O Blood: Absence of both antigens. Type AB Blood: Presence of both antigens. Type A Blood: Presence of type A antigen. Type B Blood: Presence of type B antigen.

ABO Blood Groups Antibodies are formed during infancy against the ABO antigens NOT present on your own RBCs. A baby with neither the A nor the B antigen (group O) forms both anti-A and anti-B antibodies. A baby with type A antigens (Group A) forms anti-B antibodies and so on…

Rh Blood Groups Named because one of the eight Rh antigens was originally identified in Rhesus monkeys. Later the same antigen was discovered in human beings. Most Americans are Rh+ (Rh positive), meaning that their RBCs carry the Rh antigen.

Rh Blood Groups Anti-Rh antibodies are NOT automatically formed and present in the blood of Rh- . If an Rh- person receives Rh+ blood, shortly after the transfusion his/her immune system becomes sensitized and begins producing anti-Rh+ antibodies against the foreign blood type. Hemolysis (rupture of RBCs) does not occur with the first transfusion because it takes time for the body to react and start making antibodies. But the second and every time thereafter, a typical transfusion reaction occurs.

Rh-Related Problem in Pregnancy An important Rh-related problem occurs in pregnant Rh- women who are carrying Rh+ babies. The first such pregnancy usually results in the delivery of a healthy baby.

Rh-Related Problem in Pregnancy Because the mother is sensitized by Rh+ antigens that have passed through her bloodstream, she will form anti-Rh+ antibodies unless treated with RhoGAM shortly after giving birth. RhoGAM is an immune serum that prevents this sensitization and her subsequent immune response.

Rh-Related Problem in Pregnancy If the Rh- mother is not treated with RhoGAM and becomes pregnant a second time with a Rh+ baby, her antibodies will cross through the placenta and destroy the baby’s RBCs. The baby will be anemic and becomes hypoxic. Brain damage and even death may occur unless fetal transfusions are done before birth to provide more RBCs for O2 transport.

Blood Typing The importance of determining the blood group of both the donor and the recipient BEFORE blood is transfused is glaringly obvious. Blood typing involves testing the blood by mixing it with two different types of immune serum- Anti-A Anti-B Typing for Rh factors is done in the same manner as ABO blood typing.

Blood Typing Type A Blood: Type B Blood: Type AB Blood: Type O Blood: Agglutination occurs only when mixed with the anti-A serum Type B Blood: Agglutination occurs only when mixed with anti-B serum Type AB Blood: Agglutination occurs when mixed with both the anti-A serum and the anti-B serum. Type O Blood: No agglutination occurs when mixed with either serum.

Blood Typing Since it is critical that blood groups be compatible, crossmatching is done. Cross matching involves testing for agglutination of donor RBCs by the recipient serum, and of the recipient’s RBCs by the donor serum. Type AB: Can receive any type of blood Type O: Universal donor