PDF
Citation
Print
ABO-incompatible transplantation (ABOi-TPL) can be used to address donor shortages and facilitate the timely provision of grafts [1, 2]. In 2022, 28.8% and 24.5% of living donor kidney and liver transplantations, respectively, conducted in Korea were ABOi-TPLs [3]. ABO-incompatible heart transplantations have been performed in other countries [4]. Measuring ABO antibodies is crucial for planning desensitization, determining the timing of transplantation, and monitoring rejection [5–7].
ABO antibody titration is also important for low-titer O whole blood (LTOWB) transfusion. LTOWB is gradually expanding beyond trauma and military situations to include pediatric and neonatal patients [8]. In Korean medical practice, LTOWB has not yet been applied; however, Korean medical professionals should begin to prepare for its introduction. Controversial issues regarding the titration method and cutoff values for LTOWB remain, which require further research and review [9].
Antibody titer tests are the most widely used method for measuring ABO antibodies in clinical practice. These tests are well-established, have been used in clinical settings for decades, and can be conducted manually. However, they are limited by their variability both within and between laboratories [10, 11]. The most basic approach to reducing variability is external quality control (QC). However, despite active external QC programs, ABO antibody titer testing standardization and/or harmonization remains unsatisfactory [12].
In 2014, a study analyzing the consistency of ABO antibody titer testing across domestic laboratories using 1 yr of external QC data was published [11]. Since then, no further research has been conducted on the current state of ABO antibody titer testing, despite increases in the practice of ABOi-TPL in recent years. To facilitate future attempts to standardize ABO antibody titer testing, we analyzed the consistency of ABO antibody titer testing across domestic laboratories.
The Korean Association of External Quality Assessment Service (KEQAS), established in 1976, is a private organization and the main institution in Korea dedicated to external QC and proficiency tests for clinical laboratories. We analyzed the results of biannual external QC for ABO antibody titers conducted by the KEQAS from 2019 to 2023. During each session, the specimen manufacturing supervisor prepared type O fresh frozen plasma and anti-A and anti-B titer tests were performed using a single specimen. The institutions can choose up to three methods to report their results. The available methods included tube-immediate spin (IS), tube-room temperature (RT), tube-anti-human globulin (AHG), tube-AHG with dithiothreitol (DTT), column agglutination technology (CAT)-RT, CAT-AHG, and CAT-AHG with DTT. Results that were within one titer of the mode for each method were deemed acceptable [13].
The numbers of participating institutions and reporting methods, annual proportion of acceptable results, and proportion of acceptable results according to testing method were calculated and analyzed. To assess variance according to the testing method (CAT vs. tube methods), a normalized parameter was established by subtracting the mean log titer for the peer group from the log titer of each laboratory test result (log2 titer of laboratory test result–mean of log2 titer for the peer group). Methods with fewer than 10 participating institutions were excluded from the evaluation.
Statistical analyses were performed using MedCalc Statistical Software (v.22.030) (MedCalc Software, Ostend, Belgium). Statistical significance was set to P<0.05.
The results of the external QC analysis over 5 yrs are shown in Table 1. From 2019 to 2023, the number of participating institutions increased from 77 to 83, and the total number of reported results increased from 123 to 137. Some institutions reported results for more than one testing method. In terms of the methods, the number of tests using CAT methods increased, whereas the number of tests using tube methods decreased.
The annual proportion of acceptable results changed little, from 94.6% in 2019 to 95.6% in 2023, with no significant differences in the results of chi-squared tests for trend (P=0.5645). The proportion of acceptable results in each session ranged from 84.0% to 100%. The overall proportions of acceptable results for the CAT and tube methods were 96.4% (1,080/1,120) and 95.3% (1422/1,492), respectively (P=0.1584; Fig. 1).
An F-test to assess the difference in variance between institutions using the CAT and tube methods (Fig. 2A) revealed no significant annual differences (P=0.507). Comparisons between CAT-AHG and tube-AHG and between CAT-RT and tube-RT revealed that the variance was lower for the tube methods than for the CAT methods (P=0.011 for CAT-AHG vs. tube-AHG, P=0.001 for CAT-RT vs. tube-RT) (Fig. 2B).
We assessed the current state of ABO antibody isoagglutinin titer testing based on the results of an external QC program by the KEQAS over 5 yrs. Since ABO antibody isoagglutinin titer testing has not yet been standardized, we focused on analyzing the changes in the proportion of acceptable results and variances therein.
The number of participating institutions most likely reflects the growing demand for testing as ABOi-TPL continues to expand. According to public data from the Health Insurance Review and Assessment Service, in 2019, 31,896 ABO antibody titer tests were performed for 4,677 patients, which increased to 38,831 tests for 5,658 patients in 2023 [14].
A previous study analyzing domestic external QC data and comparing the modes of the CAT and tube methods by dividing peer groups based on methods revealed that CAT methods showed lower variance than that of tube methods; however, the authors compared differences in titer steps, which made analyzing the actual distribution difficult [11]. In contrast, the present study focused on the actual variance, making it more practical than the previous study. This analysis revealed no significant difference between the CAT and tube methods. However, a subgroup analysis of AHG and RT methods revealed that variances were significantly lower for the tube methods than for the CAT methods. CAT methods have advantages over tube methods, including easier interpretation, and CAT results can be rechecked later. However, CAT methods are more expensive than tube methods [15]. Although CAT methods have an advantage in reproducibility, we found no evidence to support that CAT methods contribute to reducing variance. Collectively, our results suggest that both the CAT and tube methods exhibit variance, and the choice of method should be based on the advantages and limitations of each, as well as the practical circumstances in each laboratory.
Standardization and harmonization of clinical tests have long been emphasized, and their importance continues to grow across a wide range of tests [16]. Standardization has been successfully implemented for certain tests, such as lipids, creatinine, and HbA1c [17]. To achieve standardization, a reference measurement procedure and commutable reference materials must be established [16]. In 2008, the College of American Pathologists (CAP) introduced a “uniform procedure” to promote harmonization [10]. However, a follow-up report indicated that it failed to reduce interlaboratory variance [12]. The main reason for this failure is believed to be the focus on the analytical procedure rather than commutable reference materials.
Although standardization and/or harmonization have yet to be fully achieved, external QC programs in Korea have consistently shown high acceptable result proportions. However, no significant improvement was observed in the year-by-year analysis. Although the KEQAS has stricter acceptance criteria than the CAP (mode±one titer vs. mode±two titers), the consistently high acceptance proportions reflect the strong focus on ABO antibody titer testing and efforts toward quality management.
External QC of titer testing, managed by the KEQAS and CAP, is conducted in accordance with the concept of general semi-quantitative tests. Based on the distribution of the peer groups, results within a certain range around the mode are deemed acceptable. However, this method has difficulties in determining the mode when the results are tied or shifted to one side, increasing the difficulty in determining the overall variance of the results. To overcome these limitations, previous studies have suggested the use of geometric means based on log titers for external QC [18, 19]. This new approach should be considered to further improve external QC programs.
One of the limitations of titration methods is their failure to reflect in vivo activity of antibodies. Although methods utilizing complement-dependent cytotoxicity to reflect in vivo activity have been studied [20], their labor-intensive and time-consuming nature have made them impractical for clinical application. Continued advancements in testing methods are necessary, and researchers in Korea, where ABOi-TPL is practiced more frequently than in Western countries, should devote greater effort in this area.
In conclusion, we assessed the harmonization of ABO antibody titer testing based on external QC data collected by the KEQAS over 5 yrs. Overall, the participating laboratories demonstrated excellent performance without significant differences in acceptable result proportions or variance between testing methods. Continuous efforts are needed to further improve the quality of ABO antibody titer testing.
XML Download