Tests Used to Diagnose
Hemolytic Transfusion Reactions
(These tests should be compared to
pretransfusion sample results whenever
possible)
1. ABO Grouping
(Specimen - Red Top Tube):
The severity of a transfusion reaction due to incompatibility in
the ABO system is greater than that in other blood group systems.
Pre-transfusion and post-transfusion specimens of the patient,
RBCs from the segment used in the original
crossmatch and RBCs
from the blood bag (if available) should be tested.
2. DAT (Direct
Antiglobulin Test; Specimen - Lavender Top
Tube): At the time of a transfusion
reaction, the DAT may be + or -, depending on the type of antibody
involved and the degree of cell lysis at the
time the specimen is drawn. A positive DAT (+ DAT) usually indicates the
presence of_ recipient antibody on the surface of donor
RBC’s. NOTE: A + DAT may be due to infusion
of ABO incompatible plasma which frequently occurs in platelet
transfusion. Although this rarely causes RBC destruction, the + DAT may
cause confusion in interpreting other evidence of a hemolytic
transfusion reaction.
3. IAT (Indirect
Antiglobulin Test; Specimen - Red Top Tube):
A positive IAT indicates the presence of
free antibody in the patient’s serum. The antibody screening test will
be negative only if all the antibodies are bound to
RBCs. This may be the situation immediately following the
transfusion; however, the antibody will reappear in the serum within a
few hours to days.
4. Plasma Free
Hemoglobin: In intravascular hemolysis,
hemoglobin is released directly into the bloodstream. It is bound to
haptoglobin, a plasma protein, and transported to the RE system where it
is catabolized. Haptoglobin binding
capacity is rapidly saturated, so the level of free plasma hemoglobin
rises. An increase in plasma free hemoglobin is characteristic of
intravascular hemolysis. It is not necessary to perform a haptoglobin
test if free hemoglobin is visible in the plasma.
5. Haptoglobin
(Specimen - Red Top Tube): When
haptoglobin becomes saturated with hemoglobin, the hemoglobin-haptoglobin
complex is removed by the RE system. Since the removal of this complex
exceeds the synthetic capacity of the liver to produce haptoglobin,
plasma haptoglobin levels are decreased in intravascular hemolysis.
NOTE: Because there are other reasons for low haptoglobin levels, a low
post-transfusion haptoglobin is meaningful only when compared with a
pre-transfusion value.
6.
Hemoglobinuria/Hemosiderinuria
(Specimen - Urine): Intact
RBCs in the urine (Hematuria)
is a sign of hemorrhage in the urinary tract and is not caused by
hemolytic transfusion reactions. Free hemoglobin in the plasma
is filtered by the kidney and excreted in the
urine. Hemoglobinuria occurs following intravascular hemolysis. When
hemolysis is chronic (example: autoimmune hemolytic anemia) the heme
iron is stored as hemosiderin in the renal epithelial cells. Prussian
blue staining of urinary sediment is evidence of hemosiderin and
indicates chronic RBC destruction.
7. Bilirubin
(Total and Indirect): (Specimen - Red Top Tube):
Bilirubin, the breakdown product of the heme portion of
hemoglobin, is released into the circulation (unconjugated
or indirect bilirubin), binds to albumin and is carried to the liver
where is conjugated with glucuronates. In
both intravascular and extravascular
hemolysis, the plasma level of unconjugated
bilirubin is elevated. The presence of bilirubin in the plasma is rarely
observed in less than 6 hours. For this reason, plasma bilirubin should
be drawn 6-8 hours after a suspected hemolytic reaction.
8. Coagulation
Tests (Specimen - Blue Top Tube): DIC
is a significant sequela to massive
intravascular hemolysis. For this reason, post-transfusion specimens
drawn immediately after the reaction provide diagnostic information.
These tests should include PT/PTT fibrinogen Ddimer,
and platelet count.
9. Serum
Creatinine (Specimen - Red Top Tube):
An immediate post-transfusion
creatinine determination provides evidence
of baseline renal function. The renal involvement following an acute,
hemolytic transfusion reaction is due to hypotension in which blood flow
to the kidney is severely restricted. Although free hemoglobin is found
in the kidney tubules, it is not the cause of the ischemia. Free
hemoglobin itself is not toxic. |