Question 1

Which of the following is true regarding the mechanism of warm-reactive autoimmune hemolytic anemia?

Accepted Answer

Red cell destruction in warm-reactive autoimmune hemolytic anemia is caused by IgG autoantibodies.IgG-sensitized red blood cells are removed from circulation by macrophages in the spleen.

Question 2

All of the following have been linked to excess erythrocyte destruction except

Accepted Answer

Of the items listed,only IgE antibodies have not been associated with excess red cell destruction.

Question 3

Red cell agglutination is found on a blood film.Select the best course of action.

Accepted Answer

When red cell agglutination is noted on a blood film,the blood should be warmed to 37° C for 15 minutes and the automated analysis of the specimen repeated while the blood is warm.This patient most likely has a cold agglutinin,and it will disassociate from the red cell membrane and agglutination reverse when the specimen is warmed.Valid results can thus be obtained.

Question 4

Which of the following is most often the result of human error?

Accepted Answer

An immediate transfusion reaction,often because of ABO incompatibility,is most often the result of human error.Erythroblastosis,whether because of ABO or anti-D,occurs as a result of a maternal-fetal incompatibility.A delayed hemolytic transfusion reaction occurs as a result of undetected alloantibodies,where the level of antibody was below the level of sensitivity at the time of transfusion.

Question 5

A type-A Rh-negative infant has spherocytes on his blood film and a weakly positive direct antiglobulin test.What antibody will most likely be found on the infant's red cells?

Accepted Answer

This occurs in infants whose mothers make an IgG anti-A (in this case)or anti-B at a low level.The disease is usually mild because most ABO antibodies are IgM and do not cross the placenta because of their large size.

Question 6

A warm-reactive autoimmune hemolytic anemia found in combination with thrombocytopenia in a patient is called

Accepted Answer

When thrombocytopenia and a warm-reactive autoimmune hemolytic anemia are found together,the clinical condition is called Evans syndrome.This syndrome occurs primarily in children.

Question 7

Which of the following causes of alloimmune hemolytic anemia accounts for the largest number of deaths?

Accepted Answer

Of those situations listed,ABO blood type errors from patient misidentification account for the largest number of deaths.

Question 8

An Rh-negative woman is pregnant with her third child.She received little or no prenatal care during the first two pregnancies.Her anti-D titer is 1:512 at 30 weeks of gestation.What is the likely outcome for the baby?

Accepted Answer

This baby will most likely have Rh hemolytic disease of the newborn.The mother's antibody titer does not predict the severity of hemolytic disease of the newborn.

Question 9

Secondary cold-reactive autoimmune hemolytic anemia is found most often in patients with

Accepted Answer

Cold-reactive autoimmune hemolytic anemia is sometimes secondary after infections with organisms such as M.pneumoniae and Epstein Barr Virus (infectious mononucleosis).

Question 10

A patient's blood film shows a moderate number of spherocytes and polychromasia.Select the best test to distinguish warm autoimmune hemolytic anemia from hereditary spherocytosis.

Accepted Answer

The only one of these tests that distinguishes warm autoimmune hemolytic anemia from hereditary spherocytosis is the direct antiglobulin test,which is positive in warm autoimmune hemolytic anemia and negative in hereditary spherocytosis.

Question 11

Monospecific anti-C3b/C3d reveals agglutination with patient's red cells.Monospecific IgG antisera gives a negative result.Which red cell morphology would most likely be observed?

Accepted Answer

When only complement is present on the membrane,giving a positive direct antiglobulin test using monospecific anti-C3b/C3d,a cold agglutinin is most likely present.Agglutination of red blood cells (RBCs)would be seen on the blood provided it is at room temperature.

Question 12

The Donath-Landsteiner antibody

Accepted Answer

The Donath-Landsteiner antibody is found in paroxysmal cold hemoglobinuria.It is demonstrated by adding patient serum to donor RBCs that have been chilled to 4° C.The antibody binds at this temperature and activates complement.When the cells are warmed to 37° C,the antibody disassociates from the red cell membrane,after which intense hemolysis occurs because complement has been activated.This antibody is directed against the P blood group antigen.It is not associated with lymphoma but is usually idiopathic.However,it is associated with tertiary or congenital syphilis and is found after some viral infections.

Quiz 26: Extrinsic Defects Leading to Increased Erythrocyte Destruction Immune Causes