HTLV screening and confirmatory testing among blood donors in São Paulo: A cross‐sectional study

Introduction Human T‐cell lymphotropic virus types 1 and 2 (HTLV‐1/2) are transfusion‐transmissible retroviruses associated with severe diseases, and blood donor screening is mandatory in Brazil. Increasing HTLV‐related discard rates at our institution prompted this study to determine the prevalence and incidence of HTLV‐1/2 and to investigate the presence of HTLV‐3 among donations reactive in the ARCHITECT rHTLV‐I/II CMIA assay. Methods A retrospective cross‐sectional study was conducted among 220 340 volunteer blood donors at Fundação Pró‐Sangue/Hemocentro de São Paulo, Brazil, between September 2019 and July 2021. Real‐time PCR assays for HTLV‐1/2 and HTLV‐3 were performed. INNO‐LIA HTLV‐I/II was used as the confirmatory test for samples reactive in screening with the ARCHITECT rHTLV‐I/II CMIA assay. Results Among 220 340 donations, 404 (0.18%) were initially reactive by CMIA, and 223 (0.10%) were further analysed. Of these, 59 (26.5%) were confirmed HTLV‐1/2 positive by INNO‐LIA, and 42 (18.8%) were indeterminate. Annual rates of initially reactive donations were 0.20% (2019), 0.20% (2020), and 0.15% (2021). Overall HTLV prevalence was 0.027%, and incidence was 1.36 per 100 000 donations. Real‐time PCR detected HTLV DNA in 54 (24.2%) samples; no HTLV‐3 cases were identified. An S/CO cutoff ≥4.0 increased the positive predictive value from 47.6% to 66.1%. Conclusion These findings highlight the epidemiological and diagnostic challenges of HTLV‐1/2 in blood donors. Reliance solely on serological screening thresholds is limited, reinforcing the essential role of confirmatory molecular and serological testing to ensure accurate diagnosis and strengthen blood safety in Brazil.