Clinical Significance

The human immunodeficiency virus (HIV), the causative agent of Acquired ImmunoDeficiency Syndrome (AIDS), belongs to the family of retroviruses. HIV can be transmitted through sexual contact, contaminated blood, and blood products or from an HIV-infected mother to her child before, during and after birth. 

Two types of HIV, called HIV‑1 and HIV‑2, have been identified to date. HIV‑1 can be divided into 4 distantly related groups: group M (for main), group N (for non‑M, non‑O), group O (for outlier) and group P (Plantier). Based on their genetic relationship, 10 different subtypes (A to D, F to H, J, K and L) as well as several circulating recombinant forms (CRFs) have been identified within HIV‑1 group M.8,9 The large majority of HIV‑1 infections are caused by viruses belonging to group M, while geographical distribution of subtypes and CRFs within this group varies strongly. Due to differences in the sequence of immunodominant epitopes, especially in the envelope proteins of HIV‑1 group M, HIV‑1 group O and HIV‑2, specific antigens are necessary to avoid failure in the detection of an HIV infection by immunoassays. 

HIV p24 antigen in blood specimens of recently infected patients can be detected as early as 2‑3 weeks after infection. Anti‑HIV antibodies are detectable in serum from around 4 weeks post infection. The combined detection of HIV p24 antigen and anti‑HIV antibodies in 4th generation HIV screening assays leads to improved sensitivity and therefore a shorter diagnostic window compared to traditional anti‑HIV assays. 

_{Source: Roche cobas Elecsys HIV Duo method sheet, V 3.0 2023-08}