S32 © American Society for Clinical Pathology Am J Clin Pathol 2021;156:S21-S165 DOI: 10.1093/ajcp/aqab191 AJCP / Meeting AbstrActs Difference in hemoglobin %A2 between homozygous hemoglobin A and hemoglobin S-trait patients as measured by capillary electrophoresis C.M. Tucker, 1 D. Stickle 1 ; 1 Pathology, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania, UNITED STATES Introduction/Objective: Quantitation by high-performance liquid chromatography (HPLC) of hemoglobin %A2 is often not used in evaluation for thalassemia of hemoglobin S-trait patients, due to analytical interference from glycated hemoglobin S1d to increase %A2. In contrast, an increase in %A2 for S-trait when measured by capillary electropho- resis (CE) has been reported, without known analytical in- terference. This observation has not been re- evaluated in modern versions of CE, however. For validation exercises associated with startup of CE at our institution, we com- pared distributions of %A2 among A patients and S-trait patients using Sebia “Capillarys® 2” CE. Methods/Case Report: %A2 is provided in two Sebia “Capillarys® 2” methods: analysis of A1c (method 1, M1) and analysis of hemoglobin variants (method 2, M2). To minimize effect of potential preselection for thal- assemia among M2 samples, we frst evaluated distribu- tions of %A2 for A and S-trait among M1 samples. We then evaluated correlation of A2 measurements between M1 and M2. Statistical analyses were conducted using R programming. Results (if a Case Study enter NA): Using M1, %A2 for S-trait patients (2.61±0.31%, n=116) was higher than for A patients (2.11±0.27%, n=108) (p<0.001), with differ- ence=0.42-0.57 %A2 (95% confdence interval, CI). %A2 by M1 was consistently less than %A2 by M2, for both A and S-trait (p>0.25): for A, M1/M2=0.89±0.05 (n=35); for S-trait, M1/M2=0.88±0.05 (n=32). Decreased %A2 by M1 compared to M2 may in part be due to separa- tion in M1 of a glycated form of A2. Using M2, %A2 for S-trait patients (3.05±0.29%, n=32) was higher than for A patients (2.41±0.29%, n=35) (p<0.001), with dif- ference=0.50-0.76 %A2 (CI). M2 results were consistent with M1 data when combined with the observed M1/M2 ratios. Conclusion: Results suggest a physiological increase in %A2 in S-trait patients compared to A patients, not likely to be attributable to thalassemia. The average increase is ~0.6 %A2 for hemoglobin variant analysis by CE. Longitudinal Study of SARS-CoV-2 Antibody Characteristics Using Label-Free Immunoassays Y.R. Luo, 1 C. Yun, 2 A.H. Wu, 2 K.L. Lynch, 2 I. Chakraborty 3 ; 1 Pathology, Stanford University, Palo Alto, California, UNITED STATES; 2 Laboratory Medicine, University of California San Francisco, San Francisco, California, UNITED STATES; 3 Gator Bio, Palo Alto, California, UNITED STATES Introduction/Objective: Since the start of the COVID- 19 pandemic, much research has focused on the kinetics and magnitude of humoral immune response. With the advantages of monitoring real-time immunoreactions, label-free immunoassay (LFIA) is becoming a powerful tool in serology studies. We have developed LFIAs to measure SARS- CoV-2 antibody avidity and neutraliza- tion activity in a cohort of COVID-19 patients and deter- mine if they correlate with antibody concentration. Serial serum samples collected from mild to severe COVID-19 patients were measured out to 8 months post-symptom onset to determine the durability of the neutralizing an- tibody response. Methods/Case Report: Based on thin-flm interferom- etry technology, we established a label-free IgG avidity assay and a label-free surrogate virus neutralization test (LF-sVNT). For measurement, sensing probes pre-coated with receptor-binding domain (RBD) of SARS-CoV-2 spike protein are applied to serum samples containing SARS-CoV-2 antibodies. The label-free IgG avidity assay measures the binding strength between RBD and IgG under urea dissociation. The LF-sVNT analyzes the binding ability of RBD to ACE2 after neutralizing RBD with antibodies. Results (if a Case Study enter NA): IgG avidity indices and neutralizing antibody titers (IC50) were deter- mined from serum samples (n=246) from COVID-19 patients (n=113). IgG concentrations were measured using a fluorescent immunoassay. The neutralizing antibody titers showed a weak correlation with IgG concentrations and no correlation with IgG avidity indices. Over the time course up to 8 months post- symptom onset, IgG concentrations and neutralizing antibody titers presented similar trends: an initial rise, plateau and then in some cases a gradual decline after 40 days. The IgG avidity indices, in the same cases, plateaued after the initial rise. Conclusion: The results demonstrated that LFIA could be used an excellent solution in the determination of SARS- CoV-2 antibody characteristics. The study found that IgG concentration and neutralizing antibody titer declined over time, while IgG avidity index remained con- stant after reaching a plateau. The decline of antibody neutralization activity can be attributed to the reduction in antibody quantity rather than the deterioration of an- tibody quality, as measured by antibody avidity. Profciency Testing Performance for Point of Care Glucose Users in a Tertiary Hospital in Kenya F.M. Mukunya, 1 A.A. Amayo, 1 A. Ongeso, 2 A. Gitau 3 ; 1 Clinical Chemistry, University of Nairobi, Nairobi, Downloaded from https://academic.oup.com/ajcp/article/156/Supplement_1/S32/6413105 by guest on 28 April 2023