Hemoglobin S monitoring on TOSOH G8 in hemoglobin A1c mode in case of urgent red blood cell exchange

BACKGROUND: Pre- and post-transfusion hemoglobin S (HbS) levels are used to document the efficacy of red blood cell exchange (RCE) in patients with sickle cell disease (SCD). In case of urgent RCE a 24/7 short turn-around time (STAT) analysis, with the ability to identify and quantify HbS, is warranted. The use of TOSOH G8 (Tosoh Europe) is evaluated for this purpose, using the variant HbA1c mode. METHODS: Analytical performance of the HbS analysis on TOSOH G8 in variant HbA1c mode was evaluated, including assessment of imprecision and linearity for HbS. In addition, a comparison study between TOSOH G8 and Minicap Flex Piercing (FP) system CZE (Sebia) using 32 HbS samples (HbS range: 9%-93%) was carried out to evaluate analytical and clinical concordance. RESULTS: Total HbS imprecision was 1.77% and 0.31% for a sickle cell trait and a sickle cell anemia sample, respectively. An acceptable linearity (HbS range: 6%-88%) was observed (R2  > .99). Passing-Bablok regression analysis showed a significant proportional bias; however, a good analytical concordance (r > .95) was found. Our results suggested that TOSOH G8 underestimated HbS results compared with those of Minicap FP system (mean difference: -3.54%), especially in samples with a high HbS concentration. CONCLUSION: Hemoglobin S results obtained with TOSOH G8 in variant HbA1c mode are clinically acceptable to monitor urgent RCE. The observed underestimation will not alter clinical decision-making.