Blood System Portfolio: ABO Group

The ABO blood group system was first discovered in 1901 by Karl Landsteiner. In 1902 Sturli and Von Decastello discovered the AB group. The ABH antigens do not develop until about 6 weeks of fetal life and the concentration of antigens increases until 3-4 years of age and level out. Antibodies to the ABO blood group are naturally occurring, meaning that the body will develop immunity without previous exposure to the other blood type antigens. They are high titer antibodies and will bind an activate complement in vivo. Antibodies are not able to be detected in serum until 3-6 months of age and titers decrease markedly after the age of 65.

When classifying an individuals blood type is it typically referred to by the forward and reverse groupings. For example, if someone is blood type A, they will have naturally occurring antibodies to type B. That is why it is very important when selecting blood products for a patient that every precaution is taken to match the blood types as best as possible. The ABO antibodies are clinically significant and the hemolytic reactions are immediate and hemolytic.

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The ABH genes that encode for the ABO blood group system encode for a glycosyl transferase enzyme that adds a specific monosaccharide to a precursor substance which results in a distinguishable antigenic structure. The B gene encodes for a-3-D-galactosyltransferase which adds the D-galactose sugar resulting in the B antigen on the RBC surface. The A gene encodes for a-3-N-acetylgalactosaminyltransferase which adds the N-acetyl-D-galactosamine sugar resulting in the A antigen. The H gene encodes for the a-2-L-fucosyltransferase which adds the L-fucose sugar resulting in the H antigen.

The ABH antigens are membrane bound glycolipids. All ABH antigens have type 2 precursors that are chains linked by a 1,4 linkage. To have an A antigen, the H antigen MUST be present. Same with the B antigen, but absence of the A and B antigens with the H antigen present is considered type “O”. The ABO genes are located on chromosome #9 and there are 4 major alleles; A1, A2, B and O. A1 is codominant with B. A2 is recessive to A1, but also codominant with B. O is recessive to all other alleles. The H gene is located on chromosome #19 and there are 2 alleles that can be expressed. H encodes for fucosyltransferase, and “h” is an amorph. Individuals that have the phenotype “hh” are considered to have the bombay phenotype and are extremely rare. These individuals will not produce the H antigen, therefore there are no A or B antigens as well. It doesn’t matter if the genes for the A and B antigens are present, without the H antigen, there can be no A or B antigen production.

ABO antibodies are primarily IgM that react at room temperature and sometimes at 37 degrees celsius. The antibodies follow Landsteiners law which states an individual possesses antibodies to ABO antigens that are absent from their own cells. As mentioned above, the forward and reverse grouping should agree. If there is a discrepancy there is further testing that can be done to distinguish the problem. Discrepancies can be found in a previous article written titled “ABO discrepancies”. One such test is called the anti-A1 lectin test. 1-8% of A2 individuals will develop anti-A1, although not clinically significant, it can cause discrepancies. Lectin is a plant seed extract that agglutinates specific human cells. It agglutinates to A1 cells, but not A2 cells. Its possible to use this test to help resolve discrepancies.

Stay tuned for the next blood group system discussed.

-Caleb

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Case Study Mini-Series; Diagnostic Process and Treatment

Diagnostic workup of a suspected patient with APL should include a case history and physical examination with focus on bleeding tendencies, recurrent infections and anemic symptoms such as fatigue or pallor. A complete blood count with a differential should be performed. During a peripheral blood smear the technologist should be looking for abnormal promyelocytes with abundant azurophilic granulation and multiple auer rods. A bone marrow aspirate with cytology, cytochemistry, immunophenotyping, FISH, RT-PCR, and cytogenetics should be included. Diagnostic coagulation tests such as PT, aPTT, fibrinogen, and a D-dimer should be performed. During the immunophenotyping the characteristic phenotype of APL is CD33, CD13, CD45, CD64, and CD117 positive. Also APL is HLA-Dr negative which differentiates it from other AMLs which are HLA-Dr positive.

Early initiation of induction therapy ATRA before confirmation of diagnosis has changed the management of APL. APL is curable due to the initiation of ATRA. APL is considered a severe hematologic emergency due to its rapidly progressing bleeding diathesis and risk of intracerebral hemorrhage. Making a presumptive diagnosis based on the peripheral blood smear and bone marrow aspirate along with the patient history is important because the earlier that the patient begins therapy the better the outcome. ATRA and blood product support should be started as early as possible. APL blasts are highly sensitive to anthracyclines. Anthracycline chemotherapy with combination ATRA boasts remission rates of more than 90%. ATRA otherwise known as all-trans retinoic acid is a derivative of retinoic acid which reverses the differentiation block of APL blasts. Arsenic therapy with arsenic trioxide is approved in Europe and the United States for relapsed and refractory APL.

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Aggressive supportive therapy involves FFP, cryoprecipitate and platelets to maintain platelet levels greater than 30,000-50,000/uL and fibrinogen levels above 150 mg/dL. This regimen typically lasts during the first week of induction therapy while the coagulation disorder resolves.

There are significant adverse effects with therapy for APL. A common complication during induction therapy with ATRA or ATO (arsenic) is the development of hyperleukocytosis. APL differentiation syndrome is a life-threatening complication that develops a fever, edema/weight gain, respiratory distress, lung infiltrates, and pleural or pericardial effusions. Differentiation syndrome typically occurs within the first two weeks of the onset of therapy. Intravenous Dexamethasone is recommended immediately in the suspicion of APL differentiation syndrome. In mild cases of differentiation syndrome, ATRA or ATO therapy can just be interrupted and continued after symptoms regressed and when leukocyte counts decrease. Arsenic trioxide toxicity causes electrolyte shifts, particularly involving potassium and magnesium which to no surprise can alter ECG readings causing most commonly a QT interval prolongation. ATO therapy must be discontinued in severe prolongations due to the increased risk of cardiac arrhythmias. Documented chemotherapy adverse effects include the typical nausea and vomiting, increased infections, anemia, thrombocytopenia, increased bleeding tendencies which is exacerbated due to the coagulopathy associated with APL, and cardiac effects. With long-term chemotherapy there is an increased risk of drug-induced secondary malignancies.

Choice of treatment and timing of treatment is extremely important. As mentioned earlier it is very important to start induction therapy upon the first suspicion of APL, even before molecular confirmation occurs.

-Caleb

Transfusion Reactions

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The blood bank of any laboratory deals with a huge responsibility. They play a role in the initial compatibility testing of blood donor products and the recipient or patient serum. The patients serum contains naturally occurring antibodies or in certain circumstances where the patient has had a previous transfusion, the serum can contain alloantibodies that have been synthesized from previous donor blood products. Research has progressed suggesting that whole blood donor products are not as effective at replacing volume as individual components are. When a donor comes in and donates a pint of blood there are techniques that are used to separate the plasma from the blood products. Platelets are collected via an apheresis machine. When the plasma is separated out it must be frozen at >-20 degrees C within 8 hours of collection. When a patient needs plasma, it takes about 18-20 minutes to thaw and release. Fresh frozen plasma (FFP) has an expiration off 12 months.  Red blood cells are usually stored in a refrigerator at 1-6 degrees C. RBC products have an expiration of 42 days once collected. They can be frozen for 10 years if needed.

For transfusion purposes compatibility needs to be done correctly and cautiously. Platelets do not need to be ABO or Rh compatible, but if ample supply is available, its best to ABO match donors with the patient. Red blood cells absolutely need to be ABO and Rh compatible. If a compatible unit is not available then the hospital should use an O negative unit. O negative units are used as the universal donor. Plasma should be ABO compatible. Contrary to RBCs units, an AB plasma donor is considered the universal donor where in RBC products an O negative donor is the universal donor as mentioned previously. Plasma products contain the donors antibodies. When the donor is AB, they do not have anti-A, or anti-B. It is because of this principle that AB plasma is considered as the universal donor.

Even when every precaution is taken to ensure proper testing took place and compatibility testing was as objectively accurate as possible transfusion reactions can still take place. There is no way to 100% prevent them. Acute hemolytic reactions are typically the most severe and occur when ABO-incompatible blood is given. With acute hemolytic reactions fever and chills develop quickly, back and flank/pain (Renal failure) can occur with hemoglobinuria/hemoglobinemia. Bleeding and DIC can commonly be seen. Treatment is to stop transfusion immediately and volume replacement. Diuretics may be given, most commonly furosemide. Febrile non-hemolytic reactions are typically caused by transfusion of leukocytes that attack the recipient. A fever that is characterized as greater than 1 degree Celsius increase. The infusion of the leukocytes cause cytokine release such as IL-6, and TNF. Transfusion of HLA antibodies can occur as well. Antipyretics can be given to resolve. It is also recommended to infuse leukocyte reduced units in the future.

Bacterial contamination can occur which can cause sepsis. Typically there will be a rapid high fever with symptoms of rigor, shock and gastro symptoms. Bacterial contamination usually is able to be cultured from the donor bag along with the collection site. Antibiotics should be administered with support as necessary. A way to get around this is to leukoreduce donor units.

Transfusion-related Acute Lung Injury (TRALI) is an acute lung injury <6 hours after transfusion that presents with hypoxemia and lung infiltrates. The anti-HLA antibodies activate the PMNs in the lung endothelial which causes physiological stress. TRALI is 20% fatal, but treatment should be aggressive supportive care with fluids.

Acute afebrile reactions include allergic, anaphylactic, and transfusion associated circulatory overload (TACO) reactions. A typical urticarial or allergic reaction presents with localized hives/redness which is caused by a IgE hypersensitivity. Typical treatment includes antihistamines. Anaphylactic reactions are caused by anti-IgA antibodies in the recipient. Usually signifying that the recipient is also IgA deficient. Presents with hypotension, GI symptoms and fever with anti-IgA. Treatment is immediate epinephrine or transfusion with washed RBCs or platelets. TACO usually occurs with a history of cardiopulmonary disease with too rapid of blood infusion. High risk groups include the elderly and adolescents. TACO presents with dyspnea, and hypoxia during and after transfusion. Elevated BNP, JVD and BP. Treatment is to slow the rate of infusion and diuretics.

Delayed febrile reactions typically present greater than one week post transfusion. There is a positive DAT along with hyperbilirubinemia and evidence of a new alloantibody. Delayed febrile reactions are caused by a anamnestic response to re-exposure to red cell antigens. Treatment is support therapy. Graft-vs-host-disease (GVHD) is caused by cellular immune response by transfused T-lymphocytes versus the host or recipient. Presentation includes fever, diarrhea, skin rash. Treatment includes immunosuppressive therapy with supportive care. GVHD can be 90% fatal.

Delayed afebrile reactions include post transfusion purpura and iron overload. PTP is caused by a recipient antibody versus the absent platelet antigen (HPA-1a). There is a decrease in platelets, and increased bleeding. Treatment includes IVIG and plasma exchange. Its important to avoid platelet transfusion. Iron overload typically occurs when >100 units have been transfused. Liver, pancreas, and cardiac dysfunction occurs. Iron chelation is standard treatment.

All reactions are serious and should be treated as such. Its important to check for clerical error in pre-transfusion compatibility testing as that is the number one cause of transfusion related reactions.