Nucleic Acid Technology (NAT) testing for blood screening: impact of individual donation and Mini Pool – NAT testing on analytical sensitivity, screening sensitivity and clinical sensitivity

Globally, in a number of countries the donated blood is screened for serology markers for the Human immunodeficiency diseases-1/2, the Hepatitis C virus (HCV), and the Hepatitis B virus (HBV). Several medium human development index (HDI) countries with reasonably high percentage of transfusion transmitted infections (TTI) are evaluating nucleic acid technology (NAT) assays to detect these viruses. Serology assays are performed on individual samples, while NAT is performed on either the individual donation (ID) or on a wide array of minipool (MP)-NAT testing formats. The limit of detection of ID-NAT assays equals the analytical sensitivity and that of pool testing reflects the pool size dependent decreased sensitivity also known as screening sensitivity. To many end users, it is not obvious that pool testing will have less sensitivity. In this review, mathematically predicted pool size dependent increase in risk days which is applicable to assays of all technologies is substantiated with published experimental results with NAT standards, clinical NAT only detected yields and detection misses by MP-NAT. In the second half, the blood banking system in India, the donor base, and the variables in serology testing are discussed to explain the wide range of reported NAT yields at 1/300 to 1/17 753. Currently, NAT is not mandated in India, and the cost–benefit value of NAT is being seriously debated. As <5 IU/ml of HIV-1 and HBV have resulted in TTIs, and nearly 83% of the HBV NAT yields in India have <20 IU/ml viral load, the most sensitive assay in the most sensitive format needs to be practiced to ensure maximum blood safety.