Confidential unit exclusion (cue): Impact on transfusion safety

Confidential Unit Exclusion (CUE) was introduced when earlier-generation assays had lower sensitivity and longer infectious window periods for transfusion-transmitted infections. Improvements in serological and molecular testing have raised questions about its contemporary utility. This study evaluated the use and predictive performance of CUE at São João Local Health Unit Blood Bank, Porto - Portugal.

A retrospective descriptive study assessed all donations with CUE between January 1, 1999 and August 5, 2025. Donor demographics, CUE outcomes, and laboratory results were retrieved. Confirmed reactive serological and nucleic acid testing (NAT) findings were reviewed. The main analytical focus was on findings suggestive of possible window-period infection after a CUE-excluded donation. Sensitivity, specificity, and positive predictive value (PPV) were calculated; associations between CUE status and reactivity were assessed with Fisher's exact test and odds ratios (OR) with 95% confidence intervals.

Among 533,227 donations, 2289 (0.429%) underwent CUE self-exclusion. Twenty-four (1.05%) showed initially reactive markers at the time of the CUE-excluded donation or during follow-up, but none were confirmed as findings suggestive of window-period infections. CUE demonstrated a sensitivity of 0%, specificity of 0.7%, and PPV of 0%. In the 2009-2025 cohort (n = 344,666), no reactive results occurred in the CUE group, whereas 149 (0.043%) occurred in the non-CUE group. No significant association was found between CUE and reactivity (p = 0.388; OR = 2.045; 95% CI 0.286-14.627).

In this retrospective single-center cohort, CUE showed no measurable diagnostic or predictive value beyond routine screening and identifying possible window-period infections.