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

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.

Evaluation of solid-phase panreactivity with negative direct antiglobulin testing

Solid-phase red cell adherence (SPRCA) is a sensitive platform for antibody detection, but nonspecific reactions may occur. One pattern of apparent nonspecific reactivity is a panagglutinin with a negative direct antiglobulin test (DAT). The purpose of this study was to define the clinical characteristics of patients with these nonspecific reactions and their associated serologic findings. Twenty patients with panreactive SPRCA testing results were identified between November 2022 and May 2023. In addition to panagglutinins, these patients had (1) a negative polyethylene glycol (PEG) antibody detection test, (2) a negative PEG autocontrol, and (3) a negative DAT. The strength of SPRCA panreactivity and the results of eluate testing (by tube and SPRCA) were studied. Clinical characteristics of patients included age, sex, and primary diagnosis. Each patient was also assessed for evidence of hemolysis. Fourteen female and six male patients were evaluated (average age 44 years). Primary diagnoses included pregnancy (n = 10), acute bleeding (n = 4), orthopedic (n = 3), and other (n = 3). There was no clinical or laboratory evidence of hemolysis. The predominant strength of SPRCA panreactivity was evenly distributed across reaction grades (1+ to 3+). Fifty-five percent of the eluates tested in PEG showed panreactivity, consistent with warm-reactive autoantibodies, while 85 percent of eluates tested by SPRCA were panreactive. Six discrepant cases, in which PEG eluate testing was negative and solid-phase eluate testing showed panreactivity, were associated with weak solid-phase plasma panreactivity (1+). In addition, the reactivity strengths of the eluates tested by SPRCA were invariably more strongly reactive than those eluates tested in PEG. Panagglutination is a distinct SPRCA-only plasma reactivity pattern. Despite a negative PEG tube and DAT, most panagglutinins are warm-reactive autoantibodies. Fortunately, these "interfering" panagglutinins do not appear to be clinically significant and are easily managed by an alternative testing method such as PEG.

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.

Red Cell Alloantibody Screening: Comparative Analysis of Three Different Technologies

Background

The detection of irregular antibody is a critical issue in the management of red blood cell transfusion according to the Type & Screen (T&S) practice. In order to implement the T&S procedure at our blood bank, we compared three different automated analyzers based on column agglutination technique (CAT) or solid phase red cell adherence assay (SPACA) methods.

Methods

Pre-transfusion antibody screening was performed in 986 patients candidate to elective surgery at low risk for red blood cell transfusion. We tested the following kits: the three-cell panel micro-CAT system ID-DiaCell I-II-III (DiaMed), the four-cell panel solid-phase system Capture-R Ready Screen-4 (Immucor), and the four-cell panel micro-CAT system Serascan Diana-4 (Grifols). Positive results were further investigated using corresponding identification panels, and discrepant results were investigated with all the antibody identification systems.

Results

Among 986 samples, we observed 967 concordant negative results (98.1%), 8 concordant positive results (0.8% of cases), and 11 discrepant results (1.1%). Among discrepant samples, an alloantibody could been identified in two patents (anti-M, detected by Serascan Diana-4 and ID-DiaCell I, II, III; anti-Kp^a, detected by Capture-R Ready Screen-4 and Serascan Diana-4).

Conclusion

Among the evaluated technologies, the four-cell panel micro-CAT system displayed the highest sensitivity and specificity with an optimal negative predictive value. These features might be relevant to the routine implementation of the T&S transfusion strategy.