Blood Groups and Related Conditions

Erythroblastosis fetalis and hemolytic disease of the newborn (HDN) are caused by maternal anti-fetal erythrocyte antibodies, which cause a type II hypersensitivity response leading to erythrocyte destruction.

The implicated maternal antibodies are of the IgG subtype, as these are the only class of antibody that is readily able to cross the placenta.

With maternal blood types A and B, isoimmunization does NOT occur as the naturally occurring antibodies (anti-A and -B) are of the IgM type, which cannot cross the placenta.

In contrast, type O mothers who have antibodies with IgG subtype, that can cross the placenta trigger hemolysis in the fetus. That is why HDN is mainly seen in a group O mother who has a group A or B baby.

Symptoms are mild in most patients, although it can be severe in certain populations  (eg Africans and African Americans)

Unlike Rh alloimmunization reactions, ABO incompatibility reactions can occur in the 1st pregnancy because both A and B antigens are found in food and bacteria in the environment.

Use IgA deficient donor FFP for IgA deficient recipients

Each unit of PRBCs should raise the hematocrit by about 3 points per unit

Blood Transfusion

Blood stored for >7 days has decreased RBC 2,3-Diphosphoglycerate (2,3-DPG) and the 2,3-DPG is absent after >10 days. This absence results in an increased affinity for O2 and slower O2 release --> shift O2-Hb dissociation curve to the left

National guidelines (BCSH 2001, NBTC 2011) advise red cell transfusion when:

• Acute blood loss exceeds 30% of blood volume
• If the Hb is below 70g/L in an otherwise fit patient [Aim to keep Hb above 70g/L]
• If the Hb is between 80-90 g/L in a patient with cardiovascular disease [aim to keep Hb above 80 g/L]
• These criteria can also be applied to critically ill patients without acute bleeding.
• In all cases the clinical context must be considered and not just the patient's Hb level.