PCH is the least common type of AIHA. It's usually seen in children who have had viral infections such as measles, mumps, chickenpox, or infectious mononucleosis. It can also occur idiopathically in adults.
In PCH, biphasic hemolysin causes red cell destruction. An IgG cold autoantibody reacts with red cells in cold areas of the body, such as the extremities, when the individual is exposed to cold. Complement binds irreversibly to the red cells. When the cells circulate to warmer areas of the body, the cells undergo complement-mediated hemolysis.
Common clinical symptoms:
- Sudden onset of fever
- Abdominal cramps
- Back pain
- Intermittent episodes of hemoglobinuria
Typical laboratory findings:
- Elevated bilirubin level
- Decreased hemoglobin
- Polychromatophilia, nucleated RBCs, and poikilocytosis may be present on the peripheral blood smear
- Positive DAT with complement only
- IgG may be detected on the cells if cold saline and reagents are used
The autoantibody usually reacts weakly in traditional antibody identification tests. The biphasic hemolysin in PCH has anti-P specificity. It can be demonstrated in the laboratory through the Donath-Landsteiner test.
Transfusion in adults is only necessary if the hemolysis is severe. Young children may require transfusion because the hemolysis may be more severe due to the broad thermal amplitude of the antibody. While p red cells have a better chance for survival, the incidence of p red cells in the population is very low and therefore p blood is very rare. Blood should not be withheld from patients in urgent situations so randomly selected blood may be adequate.