The utility of grey zone testing in improving blood safety

Transfusion-transmitted infections threaten blood safety. The management of samples with weak reactivity is confusing. Our study aimed to investigate the utility of grey zone (GZ) testing in the screening of the hepatitis B virus (HBV), the hepatitis C virus (HCV), and the human immunodeficiency virus (HIV).

Chemiluminescence assays (CLA) were used for the blood screening. For each infectious marker, two CLA kits were used, but for each sample, only one kit was used for each infectious marker. An S/CO ≥ 8.0 was considered reactive, and an S/CO < 0.8 was considered non-reactive. A 0.8 ≤ S/CO < 1.0 was set as GZ1, a 1.0, ≤ S/CO < 4.0 was set as GZ2, and a 4.0 ≤ S/CO < 8.0 was set as GZ3. The samples located at different GZs were separately verified using nucleic acid testing (NAT).

22,081 patients requiring blood transfusions were included in this study. The cohort had an average age of 32.6 ± 10.6 years old. HBV test kit B (0.41% reactivity and 0.58% GZ rate) was more sensitive than kit A (0.28% reactivity and 0.43% GZ rate). HCV test kit A (0.29% reactivity and 0.57% GZ rate) was more sensitive than kit B (0.27% reactivity and 0.31% GZ rate). HIV test kit A (0.10% reactivity and 0.20% GZ rate) was more sensitive than kit B (0.08% reactivity and 0.11% GZ rate). All the samples in GZ1 were negative for NAT. HBV test kit A has negativities of 20.00% and 4.35% in GZ2 and GZ3, respectively, while HBV test kit B has negativities of 36.84% and 35.48% in GZ2 and GZ3, respectively. HCV test kit A has negativities of 100.00% and 66.67% in GZ2 and GZ3, respectively, while HCV test kit B has negativities of 72.73% and 27.78% in GZ2 and GZ3, respectively. HIV test kit A has negativities of 100.00% and 88.24% in GZ2 and GZ3, respectively, while HCV test kit B has negativities of 100.00% and 50.00% in GZ2 and GZ3, respectively.

The GZ is useful in blood screening for HBV, HCV, and HIV. A test kit with a high sensitivity has a low specificity. Different test kits should be set with different GZs based on their sensitivity and specificity.