(P-IG-16) Evaluating Direct Antiglobulin Test Positivity: Demographic and Clinical Insights from Blood Donors

Direct antiglobulin test (DAT) is not a routine screening test for blood donors and is usually detected during pre-transfusion compatibility testing. The consequences of a positive DAT in blood donors are controversial. This study aimed to determine the frequency of positive DAT in blood donors, analyze their demographic and clinical characteristics, and explore possible associated variables.

Study

Design/Methods:

Samples from whole blood and erythrocyte donors at a blood center from April to July 2023 underwent a polyspecific DAT (PolyDAT; BIO-RAD ScanGel Coombs Anti-IgG+C3d) at 20°C and irregular antibody screening (IAS; BIO-RAD ID-DiaCell I-II-III) at 37°C in gel columns. PolyDAT-positive samples underwent monospecific DAT at 20°C (MonoDAT, IgA+IgM+IgG+C3c+C3d; BIO-RAD DC-Screening I). For IgG-positive samples, acid elution (BIO-RAD DiaCidel) was performed, and the eluate was used for IAS (BIO-RAD ID-DiaCell I-II-III) at 37°C in antiglobulin phase; complete blood count (CBC), peripheral blood smear, reticulocytes, bilirubin, and haptoglobin were determined. Proportions were compared with Fisher's exact test and medians with the Mann-Whitney U test. A p-value < 0.05 was considered significant (IBM SPSS v29).

Results/Findings:

Among 9,818 blood donors, 50 (0.5%) were PolyDAT-positive, and 23 (0.2%) were MonoDAT-positive (0.15% IgG; 0.02% C3d; 0.06% IgG+C3d)(Figure A). Among PolyDAT-positive donors, 68% had 1+, and 32% + to 3+. In the C3d-positive, 75% had 1+, and 25% had 2+. In the IgG-positive, 86% had +/- to 2+, and 14% had 3+ to 4+. Agglutination in the PolyDAT and MonoDAT were correlated (Rho 0.453 to 0.545, p< 0.001). A positive MonoDAT was associated with older age (p= 0.032) and a positive IAS (26.1% vs 0.3%; p< 0.001; Odds Ratio, OR= 109.05, 95% Confidence Interval, 95%CI 32.81-312.27), with 8.7% indeterminate, 13% autoantibodies (AAB), and 4.4% Anti-S. Among the IgG-positive, the eluate was negative in 42% (cold AAB) and positive in 58% (warm AAB, 21% had 1+ to 3+, and 37% had 4+); CBC was abnormal in 86% of cases, non-conjugated bilirubin elevated in 71%, and reticulocytes increased in 43%; haptoglobin levels were normal. MonoDAT-positive reported a higher frequency of medication use than negative donors (39% vs 15.8%, p< 0.001; OR= 3.43, 95%CI 1.29-8.64). No association was observed with sex, blood type, body mass index, or the number of pregnancies.

Conclusions:

The observed frequency of positive DAT in blood donors was higher than reported. Associations with age, positive IAS, and medication use were observed. Older age might be related to prolonged exposure to medications causing AAB. Donors with a second positive DAT result should be deferred. IgG DAT-positive donors presented a high frequency of abnormalities in CBC (86%) and had evidence of extravascular hemolysis (43-71%). Hence, DAT-positive donors should be promptly referred for medical diagnosis and follow-up.