A 44-year-old, African-American female with sickle cell disease (SCD) presented for evaluation of pulmonary hypertension.
Past Medical History:
Sickle cell disease, pulmonary hypertension, hepatitis C (genotype 2), iron overload secondary to transfusion, hypothyroidism, and human leukocyte antigen (HLA)-alloimmunization due to multiple blood product transfusions for a simple transfusion every 3 weeks.
Past Immunohematology History:
Patient’s RBCs phenotyped as group A, Rh positive, C-E+c+e+, K:-1, Fy(a−b−), Jk(a+b−), and S-s+. Red blood units transfused were ABO-compatible and negative for C and K antigens as per hospital policy to transfuse Rh- and K-matched RBC to patients with SCD. One month later, anti-Swain-Langley (Sla) was identified (Figure 1). This antibody is considered clinically insignificant and reactivity was observed when testing with polyethylene glycol (PEG) and low ionic-strength saline (LISS) showed <1+ reactivity with all cells tested except for the Sla antigen negative red cell. Sla is an antigen in the Knops blood group system and is destroyed by 0.2 M dithiothreitol (DTT). This technique was used, and the chemically-treated cells were used to rule out additional antibodies. Care must be taken when performing rule outs using 0.2 M DTT-treated cells because antigens other than Sla are destroyed. Antigens usually denatured or altered include Yta, JMH, Knops, LW, Kell, Lutheran, Dombrock, and Cromer blood group antigens.1 The patient remained on C and K antigen negative restrictions and received units that were crossmatch-incompatible due to the anti-Sla. Approximately 3 years later, an antibody screen was performed (Figure 2), and anti-S was suspected. Additional testing confirmed the new antibody. After the identification of anti-S the patient was restricted to receive phenotypically-matched (ABO/Rh-compatible, C, K1, Fya, Jkb, and S negative) RBC units. It was decided not to give units negative for the Fyb antigen since it is common for Africans who phenotype as Fy(a−b−) to carry a variant Fyb allele, which carries a mutation within a GATA consensus sequence preventing expression of the gene in the erythroid cells but not other cells.2
Temperature was 36.7°C, heart rate was 70 bpm, blood pressure was 119/74, weight was 84.1 kg, O2 saturation was 95%, and room air=yes.
No acute distress, interactive.
Normocephalic, pupils equal, round and reactive to light, extraocular movements intact, mouth without erythema, lesions, or exudates, no jugular venous distention, and no carotid bruits.
Clear to auscultation bilaterally, no rales, rhonchi, or wheezing, good aeration.
Regular rate and rhythm.
No edema, no cyanosis, 1+ digital clubbing.
Current Immunohematology Findings:
Patient continued to receive phenotypically matched RBC units. The most recent sample indicates a third antibody is present. Reactivity with 2 S-negative cells was noted to be 3+, while all other S negative, Sla positive cells were 1+ in PEG and LISS (Figure 3). Two Jsa positive cells (2 and 8) reacted 3+ with patient plasma in both PEG and LISS, yet no reactivity was observed with DTT-treated cells. Anti-Jsa was suspected and confirmed.
What is the importance of transfusing phenotypically matched RBCs for patients with sickle cell disease (SCD)?
What are the serological findings indicating an antibody to a high incidence antigen may be present in plasma?
What is the primary concern when a patient sample contains a clinically insignificant antibody to a high-prevalence antigen?
How are clinically significant antibodies distinguished from clinically insignificant antibodies?
What is an approach for follow-up testing on a patient with a history of an alloantibody?
What is 1 serologic picture of a sample with an antibody to a low prevalence antigen?
What are some medical alternatives used in lieu of allogeneic blood transfusion for a patient with either multiple antibodies or a clinically significant antibody to a high-prevalence antigen when no compatible RBCs can be found?
1. Numerous institutions have distinct policies and procedures regarding transfusing patients with SCD. The majority of facilities that routinely transfuse patients with SCD transfuse RBCs matched for Rh and K antigens.3 Antigens of the Rh and Kell blood groups are well known for their immunogenicity compared to antigens of other blood groups. Chronically transfused patients are more likely to develop clinically significant alloantibodies with each additional blood infusion. In a study performed by Heddle and colleagues,4 the frequency of alloimmunization after blood transfusion was about 2.8% of the study population. Furthermore, they postulated that patients with hematological disorders had a higher percentage (5.2%) of alloimmunization due to a higher antigenic exposure rate from a greater number of infusions. Transfusing partially phenotypically similar RBCs limits the chances of developing clinically significant antibodies. However, in a study by Higgins and Sloan,5 the increased frequency of alloimmunization by SCD patients could not be substantiated. In fact, the study concluded that whether a patient becomes alloimmunized was almost independent to the number of transfusions he or she has received. Furthermore, the study did find some collaborating evidence supporting the idea that a small group in the population does have a greater risk of alloimmunization independent of disease state or age.
2. All (or a majority of) initial reagent panel cells tested are reactive in a uniform pattern in terms of both strength and test phase with negative auto control as shown in Figure 1. The only cell that is negative is number 7, and this cell lacks the Swain-Langley (Sla) antigen. A patient’s ethnicity may be an additional clue. Anti-Sla is usually associated with African ethnicity because the antigen prevalence in African-American persons is much lower than in Caucasians.6
3. The primary concern is missing the detection of underlying clinically significant alloantibodies that may be masked. In this case, the clinically insignificant anti-Sla is reactive with all cells (antigen present on 98% of Caucasians) tested. A cell that is Sla positive may also be positive for an antigen the patient lacks, and an underlying alloantibody may be missed if reactivity is accounted for by the anti-Sla. Since the Sla antigen is destroyed by 0.2 M dithiothreitol (DTT), reagent cells could be rendered Sla negative allowing identification of anti-C, Fya, Jkb, and S to be made if present. Using this technique, anti-S was identified (Figure 2). Knowing that some antigens other than Sla are destroyed by 0.2 M DTT, a good practice of using multiple techniques should be employed. In this case, 2 reagent cells negative for Sla and S but positive for Jsa were included in the selected panel (Figure 3). This allowed for the detection and identification of anti-Jsa. The Jsa antibody is directed to the low-prevalence Jsa antigen in the Kell blood group system and is considered clinically significant. Other antibodies directed to antigens not affected by DTT were ruled out.
4. An antibody is generally classified as clinically significant based on its association with hemolytic disease of the fetus and newborn (HDFN), hemolytic transfusion reactions, or decreased red cell survival. If an antibody is determined to be clinically significant, it is imperative to select antigen negative, crossmatch compatible blood for transfusion recipients. Typically, antibodies reacting at room temperature or colder are considered clinically insignificant. Antibodies reacting at 37°C or the antiglobulin phase are usually clinically significant.1
5. A reactive antibody screen can be expected from a patient with a previous alloantibody history. A red cell reagent exclusion panel should be selected using reagent cells that are negative for the patient’s corresponding antibody. All other alloantibodies must be excluded with the patient’s plasma. If the antibody is not demonstrating in the current sample and the antibody has been determined to be clinically significant, the antibody must be honored. Antigen-negative, ABO/Rh crossmatch compatible blood should be provided. Medical exceptions may occur in the event of an emergency release of uncrossmatched blood due to limited inventory or when time does not permit a full workup of the patient’s plasma. A medical release must be obtained and kept on record in the blood bank for the emergency release. Group O RBCs are issued if the patient’s ABO is unknown, and Rh negative RBCs are issued to women of child-bearing age or when the Rh typing is unknown.7 All standard immunohematology testing must be performed as soon as possible, and the attending physician must be informed promptly if any new information is obtained.
6. In a case where an entire reagent panel is tested with a patient’s plasma, antibodies to a low-prevalence antigen may present as 1 or 2 reactive red cells on the panel with a negative autocontrol. Reagent red cells are made from individual donor cells with varied antigen expressions, and the reagent panel represents antigens found in the general population. Further investigation to explain the positive reactivity, if noted, must take place. Once the antibody is identified, compatibility testing for the patient with an antibody to a low-prevalence antigen is usually a matter of crossmatching patient plasma with random donors if the antibody is demonstrable in the current sample.
7. Some alternatives to allogeneic blood transfusion include: collection of autologous blood, recombinant growth factors such as erythropoietin (EPO) or granulocyte colony stimulating factor (G-CSF),1 hydroxyurea for treatment of adults with SCD,8 volume expanders (lactated ringer’s solution, saline), “cell saver” mechanisms, iron therapy, and stem cell transplants.7
This case study was done as a group writing assignment as part of the NIH Clinical Center, Department of Transfusion Medicine, Specialist in Blood Bank Technology program (http://www.cc.nih.gov/dtm/research/sbb.html)
The authors are employees of the National Institutes of Health, Bethesda, MD. This article represents authors’ personal views and not necessarily the views of the NIH.