Comparison between screening and confirmatory serological assays in blood donors in a region of South Italy.
BACKGROUND
Screening assays are needed in order to guarantee safety of donated blood, but a significant number of safe donations are removed from blood supply because of reactive screening results. It is important to evaluate the positive predictive value (PPV) of screening assays in order to modulate confirmatory algorithm and implement an adequate counseling.


METHODS
An analysis of 17,912 blood donations has been conducted at Transfusion Medicine at Second University Naples, Italy, in 2009-2012. Serological screening for syphilis, hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV) was performed by ARCHITECT (Abbott Diagnostics, Wiesbaden, Germany); repeatedly reactive (RR) samples were checked by respective confirmatory tests. The relationship between sample/cutoff and confirmed seropositivity were analyzed.


RESULTS
RR rates were low as expected in blood donors: 0.47% for syphilis, 0.42% for HBV, 0.50% for HCV, and 0.15% for HIV. The specificity on RR + gray zone (GZ) was 99.67%, 99.79%, 99.77%, and 99.88%, respectively; due to the low prevalence, PPV value was 30.6% for syphilis, 50.7% for HBV, 42.2% for HCV, and 18.5% for HIV. These values increased substantially reaching a plateau of 89.3% for syphilis, 94.6% for HBV, 85.7% for HCV, and 100% for HIV at the threshold established by receiver operating characteristics curve analysis.


CONCLUSIONS
Supplemental testing on samples with high signal by screening assays seems to add little information. GZ settings and confirmatory testing for positive screening results should be designed taking in account several factors, including difference in the natural history among blood-borne infections, the characteristics of first- and second-level tests, and, when available, the results of nucleic acid amplification testing.
U.O.C. Immunohematology, Transfusion Medicine and Transplant Immunology (SIMT), Azienda Universitaria Policlinico (AOU), Second University of Naples, Italy.
Linda
L
Sommese
Carmela
C
Iannone
Francesco
F
Cacciatore
Gustavo
G
De Iorio
Claudio
C
Napoli
D000465:Algorithms; D001782:Blood Donors; D001803:Blood Transfusion; D017848:Blood-Borne Pathogens; D015658:HIV Infections / Q000517:prevention & control / Q000635:transmission; D006509:Hepatitis B / Q000517:prevention & control / Q000635:transmission; D006526:Hepatitis C / Q000517:prevention & control / Q000635:transmission; D006801:Humans; D007558:Italy; D018580:Mandatory Testing; D012698:Serologic Tests / Q000379:methods; D013587:Syphilis / Q000517:prevention & control / Q000635:transmission
CMIA; NAT; blood screening; confirmatory assays; transfusion-transmitted infections