International Journal of Medical Laboratory 2015;2(1):58-64. Original Article * Corresponding author: Hematology and Blood Banking Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Tel: 0098-09158075948, E-mail address: Shams8869@yahoo.com Evaluation of HIV Indeterminate Confirmatory Test Results of Blood Donors in Northeast of Iran Seyyede Fatemeh Shams 1* M.Sc., Zahra Arian pour 2 M.Sc., Farzad Molahosseini Foomani 2 M.Sc., Hossein Gholi Noori 2 B.Sc. 1 Hematology and Blood Banking Department, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. 2 Blood Transfusion Organization Research Center, Mashhad, Iran. A B S T R A C T Article history Received 25 Feb 2015 Accepted 10 Apr 2015 Available online 11 May 2015 Keywords HIV Indeterminate RIBA Western blot Background and Aims: Human Immunodeficiency virus (HIV) is spreading rapidly among the people worldwide. Infection with this virus leads to immune suppression and finally acquired immune deficiency syndrome. Early HIV detection is dependent on antibody screening against virus by enzyme linked immunosorbent assay (ELISA). Some confirmatory tests such as western blot and recombinant immunoblotting assay (RIBA) are used to verify viral infection. Many of the confirmatory test results are indeterminate. The aim of this study was to compare the frequency and patterns of indeterminate results of confirmatory tests in two groups; blood donors and patients with high risk behaviors in the northeast of Iran. Materials and methods: This is a cross-sectional study from October 2009 to March 2014. A total number of 1055 serum samples with previous positive HIV ELISA test history were tested in our laboratory, some by RIBA and some by western blot method. Results: Most of the indeterminate results belonged to blood donors and western blot analysis. The most reacting band was P24 in both methods and groups. Conclusion: RIBA assay is more sensitive and reliable than western blot, but it is necessary to use other supplementary tests with less indistinctive results. It is necessary to pay attention to HIV glycoprotein reactivity in some methods, too.