Antibody of undetermined specificity: frequency, laboratory features, and natural history

Comparison of the Detection Rate and Specificity of Irregular Red Blood Cell Antibodies Between First-Time Pregnant Women and Women With a History of Multiple Pregnancies Among 18,010 Chinese Women

Background: There is insufficient evidence to assess the risk of the production of clinically important alloimmune irregular red blood cell (RBC) antibodies in first-time pregnant women. Methods: Using the microcolumn gel antiglobulin method, 18,010 Chinese women with a history of pregnancy and pregnant women were screened for irregular RBC antibodies, and for those with positive test results, antibody specificity was determined. The detection rate and specificity of irregular RBC antibodies in women with a history of multiple pregnancies (two or more) and first-time pregnant women were determined. Results: In addition to 25 patients who passively acquired anti-D antibodies via an intravenous anti-D immunoglobulin injection, irregular RBC antibodies were detected in 121 (0.67%) of the 18,010 women. Irregular RBC antibodies were detected in 93 (0.71%) of the 13,027 women with a history of multiple pregnancies, and antibody specificity was distributed mainly in the Rh, MNSs, Lewis, and Kidd blood group systems; irregular RBC antibodies were detected in 28 (0.56%) of the 4983 first-time pregnant women, and the antibody specificity was distributed mainly in the MNSs, Rh, and Lewis blood group systems. The difference in the percentage of patients with irregular RBC antibodies between the two groups was insignificant (χ 2 = 1.248, P > 0.05). Of the 121 women with irregular RBC antibodies, nine had anti-Mur antibodies, and one had anti-Dia antibodies; these antibodies are clinically important but easily missed because the antigenic profile of the reagent RBCs that are commonly used in antibody screens does not include the antigens that are recognized by these antibodies. Conclusion: Irregular RBC antibody detection is clinically important for both pregnant women with a history of multiple pregnancies and first-time pregnant women. Mur and Dia should be included in the antigenic profile of reagent RBCs that are used for performing antibody screens in the Chinese population.

The impact of an antibody investigation algorithm emphasizing specificity on reducing potential false-positive warm autoantibody detection at a Canadian tertiary care centre

BACKGROUND AND OBJECTIVES

To reduce potential false-positive warm autoantibody (WAA) by solid-phase red cell adherence assay (SPRCA), our centre implemented a new antibody investigation algorithm (AIA) by classifying cases with panreactive SPRCA but negative saline-indirect antiglobulin test as 'antibody of undetermined significance' (AUS) after excluding clinically significant antibodies. We assessed the effects of the new AIA and subsequent alloantibody formation in patients with AUS.

MATERIALS AND METHODS

Samples from patients with positive SPRCA screens between 1 September 2017 and 31 August 2021 were selected for the study. Frequencies of antibodies classified by the old and new AIAs were compared using Fisher's exact test. Patient demographics, transfusion history and antibody formation in cases of AUS were collected.

RESULTS

A significant reduction in potential WAA frequencies from 127/1167 (11%) to 53/854 (6%) was observed (p < 0.001) when compared between the old and new AIAs among 2021 positive SPRCA antibody screens. While no patients with AUS later transitioned to potential WAA using the new AIA, four patients developed alloantibodies, including anti-E, anti-C, both anti-C and anti-E, and anti-Wra .

CONCLUSION

A significant reduction in the frequencies of potential false-positive WAA detection at our centre was observed after implementing the new AIA, leading to less resource and phenotypically matched red blood cell (RBC) use. Some patients still developed subsequent RBC alloimmunization, so clinically relevant alloantibodies should be carefully excluded before determining AUS, taking forming or evanescent antibodies into consideration.

Does decreasing the incubation period used in the antibody screen affect its sensitivity?

BACKGROUND

Pre-transfusion testing (PTT) encompasses a set of mandatory laboratory tests performed before red blood cell transfusion. The antibody screen, one component of PTT, commonly includes a 10-20 min incubation. The primary aim of this study was to determine if this period can be reduced when using current immunohematology methodologies.

METHODS AND MATERIALS

Antibody screens were performed on reagent samples using Glass or Gel-based column agglutination technologies (CAT) and a solid phase red cell adherence (SPRCA) assay, with incubation periods of 1, 5, 10 and 15 min, and 20 min (SPRCA assay only). For each method, the shortest period producing a minimum of a 1+ reaction with all reagent samples was considered optimal. The sensitivity of each assay using the optimal period was calculated after performing antibody screens on 100 patient samples.

RESULTS AND DISCUSSION

It was demonstrated that the incubation period in the SPRCA and Glass CAT systems can be reduced to 5 and 10 min, respectively, while achieving high assay sensitivity (98.9% in both). The incubation period in the Gel CAT system cannot be reduced from 15 min. Significant association between titre and reaction strength was observed for all three screening methods (p < 0.001 for both CAT methods, p = 0.041 for SPRCA). This study demonstrates that the incubation period used in the antibody screen can be reduced when using systems employing the Glass CAT and SPRCA methods, without affecting assay sensitivity. If confirmed, it could result in faster completion of PTT.

Immunohematological testing and transfusion management of the prenatal patient

The primary indication for immunohematological testing in the prenatal patient is to detect and identify maternal red cell antibodies. If there are antibodies that are expected to hemolyze the fetus' red cells, their strength of reactivity must be tested, and the fetus' antigen status determined. After delivery, testing is performed to assess the extent of fetomaternal hemorrhage, as a large hemorrhage may require other therapeutic interventions. Another major role for immunohematological testing is to select blood components appropriately when intrauterine transfusion is required for fetal anemia resulting from maternal alloimmunization or some other cause. Supplementation with molecular methods has transformed the practice of immunohematology, particularly as it applies to typing for the D antigen of the Rh blood group system. Notwithstanding the advances in testing, close coordination and communication between the transfusion service and the obstetrics service are the foundation for ensuring the finest care for prenatal patients, and for new mothers and their infants. This review describes testing and transfusion practices for prenatal patients, using case presentations to highlight the management of selected immunohematological findings. It also includes a discussion of key patient management topics that are currently unresolved.

Serologic reactivity of unidentified specificity in antenatal testing and hemolytic disease of the fetus and newborn: The BEST collaborative study

BACKGROUND

The clinical significance of serologic reactivity of unidentified specificity (SRUS) in pregnancy is not clear based on available literature. The aim of this study is to determine if SRUS is associated with hemolytic disease of the fetus and newborn (HDFN).

STUDY DESIGN AND METHODS

Retrospective data were collected from eight institutions over an 11-year study period (2010-2020), when available (5/8 sites). The outcome of the pregnancies with SRUS-no, mild, moderate, or severe HDFN-was determined.

RESULTS

SRUS was demonstrated in 589 pregnancies. After excluding those with incomplete data, a total of 284 pregnancies were included in the primary HDFN outcome analysis. SRUS was detected in 124 (44%) pregnancies in isolation, and none were affected by HDFN. Of 41 pregnancies with SRUS and ABO incompatibility, 37 (90%) were unaffected, and 4 (10%) were associated with mild HDFN. Of 98 pregnancies with SRUS and concurrent identifiable antibody reactivity(s), 80 (81%) were unaffected, and 19 (19%) were associated with mild to severe HDFN. There was 1 case of mild HDFN and 1 case of severe HDFN in the 21 pregnancies with SRUS, ABO incompatibility, and concurrent identifiable antibody reactivity(s), and 19 (90%) were unaffected by HDFN. Among all patients with repeat testing, newly identified alloantibodies or other antibodies were identified in 63 of 212 (30%) patients. Although most were not clinically significant, on occasion SRUS preceded clinically significant antibody(s) associated with HDFN (3%, 5/188).

CONCLUSION

The antenatal serologic finding of SRUS in isolation is not associated with HDFN but may precede clinically significant antibodies.

Implementation of a Standardized Prenatal Testing Protocol in an Integrated, Multihospital Health System

OBJECTIVES

When our institution grew into an integrated multihospital health system, we were faced with the need to standardize laboratory processes, including blood bank processes, across all locations. The purpose of this article is to describe our experience of standardizing the protocols for prenatal testing.

METHODS

For each hospital in the system, we established service tiers to define tests offered on site or referred to another location. For each prenatal test, we examined the related processes for ways to improve uniformity, efficiency, and reliability. Throughout this process of standardization, we collaborated with the clinical services to gain concurrence on the interpretation and reporting of results.

RESULTS

We created and implemented a uniform protocol for testing prenatal patients. The protocol standardized the definition of critical titer, instituted criteria to identify passively acquired anti-D, and established a process for the follow-up of women with inconsistent serologic results on Rh(D) typing.

CONCLUSIONS

Close collaboration with the clinical services ensured that our testing protocol is aligned with the needs of the integrated obstetrics service in the health system. The approach described in this article may provide a plan outline for pathologists facing similar challenges at other integrated health systems.

Prevalence and laboratorial determinants of the clinical relevance of antibodies of undetermined specificity

BACKGROUND AND OBJECTIVES

Antibodies of unknown specificity (AUS) are frequently identified in the pre-transfusion testing. These antibodies can be insignificant or potentially cause post-transfusion haemolysis. Information about the prevalence of clinically relevant AUS is still lacking. Our aim was to predict the potential clinical relevance of AUS using the monocyte monolayer assay (MMA) and to identify the clinical and laboratorial determinants of AUS' significance.

MATERIALS AND METHODS

Antibodies of unknown specificity identified at a single institution from 2015-2017 were evaluated through MMA. A monocyte index (MI) of more than 5% was predictive of potential post-transfusion haemolysis.

RESULTS

Thirty-two patients with AUS were included in the study. Of the studied AUS, 37·5% (12/32) presented with a monocyte index (MI) more than 5%. In the group of significant AUS, 41·7% of the patients presented with sickle cell disease (SCD) and the AUS were associated with Rh antibodies in 75% of the cases. In the group of insignificant AUS, only 10% of the patients had SCD and the association with Rh antibodies was detected in 20% of the cases. The presence of Rh antibodies was independently associated with the AUS clinical relevance (P = 0·012).

CONCLUSION

More than one-third of the AUS are potentially clinically relevant, and the association with Rh antibodies is predictive of AUS relevance. Services must honour AUS in the pre-transfusion process in order to ensure transfusion safety.

Transfusion-related red blood cell alloantibodies: induction and consequences

Blood transfusion is the most common procedure completed during a given hospitalization in the United States. Although often life-saving, transfusions are not risk-free. One sequela that occurs in a subset of red blood cell (RBC) transfusion recipients is the development of alloantibodies. It is estimated that only 30% of induced RBC alloantibodies are detected, given alloantibody induction and evanescence patterns, missed opportunities for alloantibody detection, and record fragmentation. Alloantibodies may be clinically significant in future transfusion scenarios, potentially resulting in acute or delayed hemolytic transfusion reactions or in difficulty locating compatible RBC units for future transfusion. Alloantibodies can also be clinically significant in future pregnancies, potentially resulting in hemolytic disease of the fetus and newborn. A better understanding of factors that impact RBC alloantibody formation may allow general or targeted preventative strategies to be developed. Animal and human studies suggest that blood donor, blood product, and transfusion recipient variables potentially influence which transfusion recipients will become alloimmunized, with genetic as well as innate/adaptive immune factors also playing a role. At present, judicious transfusion of RBCs is the primary strategy invoked in alloimmunization prevention. Other mitigation strategies include matching RBC antigens of blood donors to those of transfusion recipients or providing immunomodulatory therapies prior to blood product exposure in select recipients with a history of life-threatening alloimmunization. Multidisciplinary collaborations between providers with expertise in transfusion medicine, hematology, oncology, transplantation, obstetrics, and immunology, among other areas, are needed to better understand RBC alloimmunization and refine preventative strategies.

Red blood cell alloimmunization among hospitalized patients: transfusion reactions and low alloantibody identification rate

Background

Unexpected red blood cell alloantibodies can cause hemolytic transfusion reactions. In this study, the prevalence of alloimmunization, the rate of identification of alloantibodies and the rate of blood transfusion reactions among transfused patients were identified in a clinical emergency hospital in Brazil.

Methods

Transfusions and clinical records of patients who had a positive indirect antiglobulin test between January and December 2013 were analyzed.

Results

Of 1169 patients who received blood transfusions, 28 had positive indirect antiglobulin tests, with one patient having two positive tests at different times, resulting in 29 positive tests during the period of this study. Alloantibodies were identified in 58.6% (17/29) of the cases. In 27.5% (8/29), identification was inconclusive and it was not possible to confirm alloimmunization. The rate of red blood cell alloimmunization was 1.71% (21/1169). Of 21 cases of alloimmunization, four (19%) were unidentified due to an unusual agglutination profile. All identified alloantibodies were clinically significant (10/17 anti-Rh, 5/17 anti-Kell and 2/17 anti-MNS). In two patients who had positive indirect antiglobulin tests, one had an unidentified alloantibody, and the other had an inconclusive test and developed a hemolytic transfusion reaction.

Conclusion

The prevalence of clinically important red blood cell alloantibodies and hemolytic transfusion reactions among patients with unidentified alloantibodies suggests that specific laboratory techniques should be performed to identify alloantibodies in cases of pan-reactivity or autoantibodies to improve transfusion safety.

Patient factors associated with unidentified reactivity in solid-phase and polyethylene glycol antibody detection methods

BACKGROUND

Several publications have reported an increase in nonspecific reactions when automated technologies such as solid phase are used for the detection of red blood cell alloantibodies. However, there is little known about patient-specific factors associated with these reactions and the clinical importance of these nonspecific reactions.

STUDY DESIGN AND METHODS

We performed a 6-year retrospective review of our blood bank records and all newly reported unidentified (UID) reactivity using a test tube polyethylene glycol (t-PEG) and solid-phase method for the detection and identification of alloantibodies was recorded. Patient factors, such as underlying diagnosis, age, sex, ABO, Rh type, ethnicity, and subsequent antibody formation were recorded in each case.

RESULTS

We determined that there was a significant increase in new UID reactions recorded in solid phase (20 per 10,000 tests) when compared to the t-PEG (1.8 per 10,000 tests) method for the detection of antibodies (p ≤ 0.0001). Solid-phase UID reactions were significantly associated with female sex (p = 0.04) and certain diagnoses, such as chronic or autoimmune disease, cancer, pregnancy, surgery, and trauma. Approximately 16% of patients developed a new auto- or alloantibody subsequent to their detected UID using solid phase.

CONCLUSIONS

When solid phase is used for antibody identification, there is greater sensitivity toward nonspecific reactivity when compared to the t-PEG method. Patient sex and underlying diagnosis may explain the increased incidence of new UID reactivity in the solid-phase technology. Finally, UID reactivity should not be overlooked due to a notable percentage of subsequent clinically significant antibodies after UID detection.

Non-specific red cell reactivity in an obstetric population

OBJECTIVE

To examine non-specific red cell reactivity (NSR) on antibody (Ab) screening of obstetric inpatients.

METHODS

Observational study of 5438 obstetric inpatients (2009-2013). Ab-positive patients were identified and their records reviewed for NSR, other antibodies, transfusion reactions or hemolytic disease of the fetus/newborn (HDFN). Evaluation of NSR frequency by test era assessed the impact of an institutional change to solid-phase screening in 2011.

RESULTS

Of obstetric inpatients, 5.3% had at least one positive Ab screen; 1.6% had NSR. Of NSR-positive patients, 16.7% had identifiable Abs that pre-dated NSR; 25% had concurrent Abs and 8.5% had subsequent Ab identification. In 49.1%, NSR resolved during follow-up. The frequency of NSR was higher after the change to solid-phase Ab screening, but specific Ab frequency was similar in both testing periods. No transfusion reactions or cases of HDFN were noted in this cohort.

CONCLUSIONS

NSR is found in 1-2% of obstetrical inpatients at our institution, and has more than doubled since the initiation of solid-phase screening. Although likely clinically insignificant by itself, NSR is commonly found in relation to other red cell Abs and may precede their development.

Pathology consultation on electronic crossmatch

OBJECTIVES

The full crossmatch is traditionally the final step in compatibility testing, acting as a serologic double check for ABO compatibility and unexpected RBC antibodies. In this review, we discuss the development of electronic crossmatch (EXM), an approach for determining when EXM can be used, and its strengths and weaknesses.

METHODS

Because EXM relies on highly sensitive screening assays, antibodies are frequently encountered whose clinical significance must be investigated and interpreted. Our approach is to obtain further history, perform enhanced tube testing, and consider tests of immune reactivity or RBC survival.

RESULTS

For those without clinically significant antibodies, we found two alternatives: immediate-spin crossmatch (IS XM) and EXM. IS XM is prone to error related to serologic interference, whereas EXM depends on the accuracy of the sample label, accurate data entry, and informatics to avoid errors.

CONCLUSION

EXM is an alternative to the serologic test in patients who have no clinically significant antibodies.