HOWDOI...?

How do I approach patients with warm-reactive autoantibodies?_2985 14..17

Douglas P.Blackall

arm-reactive autoantibodies are the most test (DAT; i.e., What is coating the RBCs in excess: IgG, C3, common cause of autoimmune hemolytic or both? What is the strength of reactivity of the anti-IgG anemia, with the incidence of these anti- and anti-C3 reagents?). Having knowledge of the serologic bodies increasing with patient age.1 They reactivity of the patient’s antibody helps to confirm that it haveW been reported in children as young as a few months is, indeed, a warm-reactive autoantibody. It also provides of age, and there are two case reports of neonates who important insight into the likelihood that the antibody is seem to have developed warm-reactive autoantibodies in resulting in hemolysis—warm autoimmune hemolytic utero.2,3 They are a relatively common finding at Arkansas anemia (WAIHA). As examples, it has been well demon- Children’s Hospital, accounting for approximately 15% of strated that more strongly reactive warm autoantibodies all antibodies evaluated in the laboratory.4 Although are more likely to be associated with overt hemolysis, warm-reactive autoantibodies are sometimes idiopathic, although this is by no means a perfect correlation.4,5 Simi- there are a number of common disease associations larly, warm-reactive IgG autoantibodies that are also asso- including hematopoietic malignancies (e.g., lymphomas ciated with demonstrable C3 on the RBC membrane are and leukemias, especially chronic lymphocytic leukemia), more likely to be hemolytic via a synergistic effect.6 autoimmune disorders (e.g., systemic lupus erythemato- Once I understand the serological presentation of the sus), and chronic inflammatory conditions (e.g., Crohn’s warm-reactive autoantibody, I turn my attention to deter- disease and ulcerative colitis).1 On occasion, a warm- mining the clinical significance of the antibody and reactive autoantibody may be the harbinger of one of understanding the patient’s clinical condition. Most these disorders, which only presents in overt form later. important is determining if the antibody is associated This review will focus on the transfusion service labora- with hemolysis. This is a key consideration as this will be tory approach to these autoantibodies and applies to the primary determinant of whether or not the patient will pediatric and adult patients equally. need transfusion (now and into the future). This will, in I am usually first consulted about a new warm- turn, drive the extent to which the antibody is evaluated in reactive autoantibody by a blood bank technologist. Ini- the laboratory. To determine the clinical significance of tially, I strive to obtain information about the serologic warm-reactive autoantibodies, a number of ancillary nature of the antibody and the clinical status of the laboratory tests are required including the hemoglobin patient. With regard to the former, I turn my attention first (Hb) and hematocrit (low), the reticulocyte count (gener- to the reactive nature of the antibody in the serum (i.e., ally elevated, but reticulocytopenia can be a harbinger of a How strongly reactive is the antibody? Are all of the red difficult patient course), the lactate dehydrogenase value blood cells [RBCs] on the antibody identification panel (elevated), and the bilirubin level, particularly the indirect reactive? Are the cells on the panel equally reactive?). I fraction (elevated). A visual inspection of the plasma or next consider the reactive nature of the direct antiglobulin urine is low cost and can provide helpful information as to whether hemolysis (if present) is intravascular or extravas- cular. The latter is expected in cases of WAIHA. A hapto- From the Department of Pathology, University of Arkansas for globin value can be useful (low), but in many laboratories Medical Sciences College of Medicine and Arkansas Children’s this test is not readily available. In addition, haptoglobin is Hospital, Little Rock, Arkansas. an acute-phase reactant, so a single value, especially one Address reprint requests to: Douglas P. Blackall, MD, that is in the normal reference range for the laboratory, Department of Pathology, Arkansas Children’s Hospital, 1 Chil- may not be useful. Finally, it is always advisable to assess dren’s Way, Little Rock, AR 72202; e-mail: dougandcaron@ the RBC morphology on review of the peripheral blood att.net. smear, because spherocytes are typically identified in Received for publication July 27, 2010; revision received cases of WAIHA. September 10, 2010, and accepted October 15, 2010. If a patient is experiencing hemolysis to the extent doi: 10.1111/j.1537-2995.2010.02985.x that transfusion support is necessary, additional serologic TRANSFUSION 2011;51:14-17. work may be required. The most basic question is this:

14 TRANSFUSION Volume 51, January 2011 PATIENTS WITH WARM AUTOANTIBODIES

How much does one need to do? Before approaching this over time are an exception. The phenotype can be question, it is important to remember that when the blood used to select units of blood for transfusion that will bank is faced with a warm-reactive autoantibody and a prevent alloimmunization and can also be used to patient requires transfusion, the primary concern is the avoid antigen reexposure if the patient is already identification of underlying blood group alloantibodies. alloimmunized. Depending on the ease or difficulty As I explain to rotating residents, “we may not be able to encountered, it may be possible to provide units of do anything about an autoantibody and its consequences, blood for transfusion that are matched to the but we don’t want to contribute to further hemolysis by patient’s phenotype (i.e., Rh, Kell, Duffy, Kidd, and transfusing a patient with an underlying alloantibody.” MNS system antigens). Such a strategy would gener- Since alloantibodies form as a result of RBC exposure, via ally preempt the need to perform adsorption studies. transfusion or pregnancy, an important task for blood However, even partially antigen-matched units can bank staff is to obtain history. We are benefitted in the be effective in preventing alloimmunization in pediatric setting by generally having very accessible and patients with WAIHA.7 Matching for the most immu- reliable transfusion histories on our patients. In addition, nogenic and/or clinically significant antigens (e.g., Rh most of the patients that we serve have no history of preg- system, K antigen, Kidd system) makes the most nancy. Thus, many patients with new presentations of sense. Finally, it is important to note the increasing WAIHA have no reasonable likelihood of having underly- availability of blood group antigen genotyping. Geno- ing autoantibodies, so no special studies (e.g., adsorption) typic analysis may be particularly important in those are required before transfusion. On the other hand, if a cases in which a “clean” phenotype cannot be patient has been transfused or pregnant and there is time obtained, usually as a result of insufficient dissocia- to perform an adsorption study (based on the clinical tion of autoantibodies from the RBC membrane. status of the patient), then the safest practice is to com- • Elution studies: These studies are usually undertaken plete the study before transfusing. Very importantly, it is to identify new blood group alloantibodies, resulting critical to communicate with transfusion services that from recent transfusions, that are not yet demon- may have evaluated the patient in the past. Early knowl- strable in a patient’s plasma. Elution studies have edge of a previously identified blood group antibody can very little place in the evaluation of warm-reactive be extremely helpful. autoantibodies. Typically, if the plasma demonstrates There are a number of additional serologic issues that a pan-reactive antibody, the eluate will only confirm the transfusion service should consider in any patient pre- the same but the reactivity is generally stronger due to senting with a warm-reactive autoantibody. a concentration of the eluted antibody. Thus, one is even more unlikely to identify an alloantibody in the • Adsorption studies: These studies are important in eluate than in the plasma. I reserve elution testing for uncovering underlying alloantibodies in those patients with reactive DATs who have very weakly- patients who have a history of pregnancy or transfu- reactive antibodies in their plasma that I suspect to be sion, if time allows for such a study. In those who have autoantibodies but do not react with all panel cells. In not been transfused in the preceding 3 months, an such cases, due to the concentration effect of the autologous adsorption is indicated. For those with a eluate, it is usually possible to demonstrate pan- history of recent transfusion, a more demanding allo- reactivity, thus confirming that the antibody in ques- geneic study is required. Whether either of these tion is an autoantibody. studies will be able to be performed in house or • Crossmatching: Crossmatches are almost invariably referred out depends on a number of factors includ- reactive in patients with warm-reactive autoantibod- ing the overall sophistication of the laboratory, the ies, as these antibodies generally react with all RBCs number of such studies the laboratory encounters, tested. Crossmatching excessive numbers of units to and general financial considerations (e.g., relative identify those that are “least incompatible” provides cost of testing in house vs. referring out). no proven clinical benefit for patients.8 In other • Phenotyping: This refers to establishing which of the words, “incompatible is incompatible.” Although major, clinically significant antigens are or are not there is no disadvantage to selecting a unit for trans- present on the patient’s RBCs. This can be a powerful fusion that reacts less strongly, since there is also no resource for the laboratory as it defines the possible evidence to suggest a patient benefit, the least incom- alloantibodies that a patient can make. While pheno- patible terminology and associated clinical practice typing is a routine part of the initial work-up of should be discouraged. Although space does not patients highly prone to alloimmunization (e.g., those allow for a detailed discussion, the use of the “in vivo with sickle cell disease), it is not performed com- crossmatch” (transfusion of a small aliquot of RBCs monly for other patients. However, patients with with serologic reassessment, visual assessment of the WAIHA who will likely require frequent transfusions plasma for free Hb, and clinical evaluation) should

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also be discouraged.1 There is no practical benefit to mal cold hemoglobinuria), or warm-reactive autoan- be gained by its performance given what we under- tibodies with unusual thermal amplitudes; or even stand about the hemolytic nature of warm-reactive hemolysis that is not actually immune mediated (e.g., autoantibodies. Similar to the release of least incom- associated with a hemolytic toxin, as with a brown patible units, the in vivo crossmatch may make the recluse spider envenomation, or an overwhelming blood bank specialist and the clinician feel more at bacterial infection). The evaluation of these possibili- ease, but it is wasteful of resources and may delay ties starts with a thorough review of the patient. Most transfusion therapy. In the end, the incompatible important are a medication history and a determina- units associated with warm-reactive autoantibodies tion of any preceding or coexisting illnesses. If the should be transfused judiciously knowing that as long patient is taking, or has recently taken, a medication as alloantibodies have been investigated, these units that has been associated with hemolysis (e.g., a should have the same survival as the patient’s own second-generation cephalosporin), then an evalua- RBCs, even if diminished.9 tion for drug-dependent antibodies is warranted. This • Autoantibodies with defined specificities: Warm- will almost always take place in an immunohematol- reactive autoantibodies typically react with all ogy reference laboratory. Testing for IgA autoantibod- reagent RBCs with the same general strength of reac- ies, Donath-Landsteiner antibodies, and warm- tivity. However, they less commonly demonstrate reactive autoantibodies with unusual thermal specificity for a blood group antigen in a relative or amplitudes will likely transpire in the same setting. absolute sense. Most such antibodies demonstrate On the other hand, hemolysis resulting from a toxin enhanced reactivity for certain antigens in the Rh exposure is usually evident after reviewing the blood group system (e.g., e). More commonly, there is patient’s clinical history. a relative specificity for an antigen, meaning that the • Follow-up studies: Patients who have persistent patient’s autoantibody reacts more strongly with warm-reactive autoantibodies represent a potential reagent RBCs carrying the antigen and less strongly “resource sink” for the transfusion service. On the with antigen-negative RBCs. Sometimes, however, conservative side, one can make the argument that all the antibody has apparent absolute specificity for a such patients, with subsequent transfusions, either blood group antigen (e.g., autoanti-D). Although it is require an adsorption study or require phenotypic tempting to “honor” the specificity of these autoanti- matching to assure that alloantibodies, if present, are bodies by providing antigen-negative units of blood, avoided. With strongly reactive autoantibodies that it is unclear if these RBCs have enhanced survival in are hemolytic, this is the safest course of action to the recipient.1 It pays to remember that warm- take. On the other hand, some patients have very reactive autoantibodies are polyclonal immune weakly reactive but persistent warm autoantibodies. responses.10 Although there may be a prevailing clone At Arkansas Children’s Hospital, sickle cell patients of cells generating an antibody with a defined in vitro most frequently have this finding. We have a relatively specificity, the in vivo reality is likely more compli- large cohort of patients who developed weakly reac- cated. In practice, if it is easy to provide an antigen- tive warm autoantibodies after alloimmunization. negative unit and the crossmatch is actually Although not clinically significant, with respect to compatible (not at all a given), then I sometimes do hemolysis, they create anxiety in the laboratory as this simply to avoid the confusion that can accom- with any warm-reactive autoantibody. However, we pany the release of an incompatible unit. However, I rarely perform follow-up adsorption studies on these would not transfuse a rare antigen-negative unit (e.g., patients. Instead, we carefully monitor the strength of e–) for this reason. These units should be reserved for the DAT. If it remains weak and stable over time, we alloimmunized patients. simply transfuse the patient releasing the incompat- • Autoantibodies associated with weakly reactive or ible units that are available to us. This has proven to nonreactive DATs: Occasionally, a patient is encoun- be a very safe practice, possibly because these tered with laboratory evidence of hemolysis but a patients already receive units matched for Rh system very weakly reactive or even nonreactive DAT is seen. antigens and the K antigen. In other words, the degree of hemolysis is dispropor- tionate to the serologic character of the DAT. This can In conclusion, warm-reactive autoantibodies are be particularly vexing when the IAT findings do not fairly commonly seen in all patient ages and require point clearly to a warm-reactive autoantibody. In careful evaluation. On initial presentation, it is important cases such as these, I consider other, less common to understand the serologic and clinical features of the etiologies of hemolysis: for example, drug-associated autoantibody as these will be helpful in determining the hemolysis; hemolysis due to an IgA autoantibody, a breadth of the blood bank investigation, both at presenta- Donath-Landsteiner autoantibody (as with paroxys- tion and with follow-up testing. It is important to make

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judicious use of effective ancillary studies, such as adsorp- 3. Erler BS, Smith L, McQuiston D, Pepkowitz SH, Goldfinger tion and phenotyping, but those studies that have no D. Red cell autoantibody production in utero: a case demonstrated value for patient care (e.g., reliance on units report. Transfusion 1994;34:72-4. that are least incompatible, elution studies, in vivo cross- 4. Blackall DP. Warm-reactive autoantibodies in pediatric matching) should be discouraged and avoided. Patients patients: clinical and serologic correlations. J Pediatr with warm-reactive autoantibodies are challenging, but Hematol Oncol 2007;29:792-6. with a little extra effort on the front end, they can be 5. Wheeler C, Calhoun L, Blackall DP. Warm reactive managed successfully. The laboratory and the clinical autoantibodies: clinical and serologic correlations. Am J team can be confident that units released for transfusion, Clin Pathol 2004;122:680-5. although they are incompatible, have a high likelihood of 6. Zupanska B, Sokol RJ, Booker DJ, Stamps R. Erythrocyte being safe and efficacious for the patient. autoantibodies, the monocyte monolayer assay and in vivo haemolysis. Br J Haematol 1993;84:144-50. 7. Shirey RS, Boyd JS, Parwani AV, Tanz WS, Ness PM, King CONFLICT OF INTEREST KE. Prophylactically antigen-matched donor blood for patients with warm autoantibodies: an algorithm for trans- The author declares that he has no conflicts of interest relevant to fusion management. Transfusion 2002;42:1435-41. the manuscript submitted to TRANSFUSION. 8. Petz LD. “Least incompatible” units for transfusion in autoimmune hemolytic anemia: should we eliminate this meaningless term? A commentary for clinicians and trans- REFERENCES fusion medicine professionals. Transfusion 2003;43:1503-7. 1. Petz LD, Garratty G. Immune hemolytic anemias. 9. Salama A, Berghofer H, Mueller-Eckhardt C. Red blood cell Philadelphia: Churchill Livingstone; 2004. transfusion in warm-type autoimmune haemolytic 2. Blackall DP, Liles LH, Talati A. In utero development of a anaemia. Lancet 1992;340:1515-7. warm-reactive autoantibody in a severely jaundiced 10. Gehrs BC, Friedberg RC. Autoimmune hemolytic anemia. neonate. Transfusion 2002;42:44-7. Am J Hematol 2002;69:258-71.

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