Discussion
We describe an unusual presentation of hyperhemolysis in a beta
thalassemia major patient who presented with high grade fever, bone pain
and malaise. It was interesting to note that Day 2 DAT was negative for
anti-IgG but showed 2+ for anti-C3d. A well performed DAT detects
100-500 molecules of bound IgG per red blood cell. A negative IgG
autoantibody is a common feature in acute form of HS. There are several
reasons which may explain a negative DAT in HS. They are (a)
sensitization of the patient’s red cells with a small number of IgG
molecules which is below the threshold for detection by a standard DAT
(b) most standard DAT do not incorporate anti-IgA monoclonal reagent,
thereby, missing out on the possibility of IgA mediated hemolysis (c)
low affinity IgG autoantibodies being eluted from RBC during the washing
process4. A super Coombs test, which incorporates an
enhanced and more sensitive version of the standard DAT may be useful in
cases where the standard DAT is negative.
It is also interesting to note that the negative anti-C3d on Day 15
repeated DAT in our patient could be attributed to the immunosuppressive
corticosteroid therapy given to him.
The pathogenesis of HS is interesting. The mechanisms which may explain
HS in our patient are: (a) macrophage hyperactivation (b) RBC
alloimmunisation (c) complement regulation dysfunction (d) bystander
hemolysis (e) suppression of erythropoiesis and (f) HLA
alloimmunisation5. Macrophages are widely believed to
be in a primed state in hemoglobinopathy syndromes. In response to
allogeneic transfusion, macrophages become hyperactivated and bind to
both host and donor red blood cells resulting in rapid
destruction5. Interestingly, our patient had
significant extramedullary hematopoiesis in the spleen resulting in
hypersplenism. Since the splenic red pulp contains a large number of
macrophages, therefore this group of patients are at considerable risk
of developing HS.
Bystander hemolysis, a term coined by Petz and Garraty, is used to
describe immune hemolysis of erythrocytes in the presence of recipient
alloantibodies directed to antigen negative transfused red blood
cells6. Besides RBC alloantibodies; HLA and plasma
protein antigens from the transfused blood may react with the
recipient’s antibodies contributing to complement regulation
dysfunction, thereby leading to bystander hemolysis7.
However, in this patient, we did not perform an HLA antibody screen, and
facilities to measure levels of complement factors, C5b-9 to support our
findings of complement dysfunction were unavailable.
Besides the above, RBC alloimmunization is also an important cause of
hyperhemolysis. A negative antibody screen in our patient at Day 2 of
transfusion is a feature commonly seen in the acute form of HS. Standard
serological studies used may not be potent enough to detect low affinity
alloantibodies against low frequency antigens. Antibody dependent cell
mediated cytotoxicity (ADCC) may explain the mechanism of hemolysis in
recipients with levels of alloantibody below the serological detection
threshold8. Interestingly, anti-Cwwas subsequently detected in our patient’s serum on Day 15. This
antibody including those of the Kidd or Rh system are often undetectable
on pretransfusion testing but may increase rapidly in titer following a
blood transfusion. Re-exposure of an antigen negative recipient to a red
cell antigen positive transfusion could result in an anamnestic antibody
response, precipitating hemolysis. Anti-Cw is an
alloantibody directed against the Cw antigen (Rh 8),
which is located on the RHCE gene. This would explain the initial
presence of anti-C3d on Day 2 DAT in which, the
anti-Cw causes activation of the complement.
Cw is a low incidence antigen, and has been reported
to be 1% and 2% in Blacks and Caucasians
respectively9. Anti-Cw, usually an
IgG antibody, may occur naturally or after an immune stimulation by
blood transfusion such as seen in this patient. Unlike other Rh
antigens, anti-Cw is usually not significant.
Anti-Cw associated moderate-to-severe hemolytic
disease of the fetus and newborn (HDFN) have been reported infrequently
in case reports and thus may be of clinical significance in females of
reproductive age10. However, literature on the
significance of this antibody in acute and delayed hemolytic transfusion
reaction is severely lacking.
Severe reticulocytopenia was also an additional feature seen in our
patient. Thalassemia patients are known to have significantly lower
serum levels of erythropoietin at steady state which may trigger
neocytolysis during HS causing further destruction of erythroid
precursors11. A bone marrow analysis would be helpful
to confirm the presence of erythropoiesis suppression. Another mechanism
which could also contribute to reticulocytopenia is increased peripheral
consumption of reticulocytes by hyperactive macrophages in the presence
of preserved bone marrow activity of erythropoiesis.
Management of HS is largely dependent on the severity of anemia and
degree of hemolysis. Blood transfusion should be avoided in the milder
form of HS as they are known to exacerbate hemolysis. Combination
therapy of IVIg and steroids are synergistic in suppressing macrophage
activation and shortening hemolysis through immodulatory
effects12. Low dose IVIg at 0.4g/kg daily for 5 days
and intravenous methylprednisolone 500mg daily for 2 days are
recommended for the treatment of HS12. In severe forms
of HS, red blood cell transfusion may be required but should be given in
the presence of IVIg-steroid cover. Subcutaneous erythropoietin may have
a role in direct stimulation of erythropoieis and preventing
neocytolysis. Furthermore, since macrophage activation is an important
mechanism in HS, anti-CD20 monoclonal antibody such as rituximab
375mg/m2 even at a single dose has shown
response13. It is interesting to note that eculizumab,
a C5 convertase inhibitor which inhibits complement activation is
promising in the treatment of HS in sickle cell anemia and may also
confer such benefit in thalassemia14. On another note,
as hemolysis increases the risk of both arterial and venous thrombosis,
it is imperative to ensure adequate anticoagulation prophylaxis is given
during active HS. Splenectomy has a role in HS as it is known to resolve
HS crisis in thalassemia15. However, our patient
declined splenectomy due to personal reasons.