Translate and Read

Saturday, June 28, 2014

Updated Recommendation for Testing of HIV 1 & 2 Infection

Posted by Prahallad Panda on 10:05 PM Comments

According to a press release in 2012, the total number of people living with HIV/AIDS in India is estimated at 21 lakhs in 2011. Children (<15 yrs) account for 7% of all infections, while 86% are in the age group of 15-49 years. Of all HIV infections, 39% (8.16 lakh) are among women.
An estimated 1.1 million persons in United States were living with human immunodeficiency virus (HIV) infection as of 2010, of whom an estimated 181,000 were unaware of their infection.

940px-HIV-AIDS_world_map_-_DALY_-_WHO2004.svg
HIV F
Approximately 49,000 new HIV diagnoses are reported to Centers for Disease Control (CDC) each year.As of 2009, an estimated 83 million adults aged 18 to 64 years reported they had been tested for HIV.
Accurate laboratory diagnosis of HIV is essential to identify persons who could benefit from treatment, to reassure persons who are uninfected, and to reduce HIV transmission.
HIV immunoassays based on different design principles are generally grouped into “generations”:  
  • 1st generation—All antigens used to bind HIV antibodies are from a lysate of HIV-1 viruses grown in cell culture. An indirect immunoassay format employs labeled antihuman IgG for detection of IgG antibodies. Significant specimen dilution is required to overcome cross-reactivity with cellular protein contaminants. Examples commercially available in the United States as of May 2014 include the HIV-1 Western blot and the HIV-1 IFA.  
  • 2nd generation—Synthetic peptide or recombinant protein antigens alone or combined with viral lysates are used to bind HIV antibodies. An indirect immunoassay format employs labeled antihuman IgG or protein A (which binds to IgG with high affinity for detection of IgG antibodies. Design of the specific antigenic epitopes improves sensitivity for HIV-1 group O and HIV-2; eliminating cellular antigens that contaminate viral lysates improves specificity by eliminating cross-reactivity with cellular proteins. Examples commercially available in the United States as of May 2014 include one HIV-1 enzyme immunoassay and six rapid HIV antibody tests.
  • 3rd generation—Synthetic peptide or recombinant protein antigens are used to bind HIV antibodies in an immunometric antigen sandwich format (HIV antibodies in the specimen bind to HIV antigens on the assay substrate and to antigens conjugated to indicator molecules). This allows detection of IgM and IgG antibodies. Lower sample dilutions and the ability to detect IgM antibodies (which are expressed before IgG antibodies) increase sensitivity during early seroconversion. Examples commercially available in the United States as of May 2014 include one HIV-1/HIV-2 enzyme immunoassay and two HIV-1/HIV-2 chemiluminescent immunoassays.
  • 4th generation—Synthetic peptide or recombinant protein antigens are used in the same antigen sandwich format as 3rd generation assays to detect IgM and IgG antibodies, and monoclonal antibodies are also included to detect p24 antigen. Inclusion of p24 antigen capture allows detection of HIV-1 infection before seroconversion. These assays (termed “combo” assays”) usually do not distinguish antibody reactivity from antigen reactivity. Examples commercially available in the United States as of May 2014 include one HIV-1/HIV-2 enzyme immunoassay, one HIV-1/HIV-2 chemiluminescent immunoassay, and one HIV-1/HIV-2 rapid test that uses separate indicators for antigen and antibody reactivity.
Immediately after HIV infection, low levels of HIV-1 RNA (ribonucleic acid) might be present
intermittently, but no viral markers are consistently detectable in plasma. Approximately 10
days after infection, HIV-1 RNA becomes detectable by Nucleic Acid Test (NAT) in plasma and quantities increase to very high levels.
Next, HIV-1 p24 antigen is expressed and quantities rise to levels that can be detected by 4th generation immunoassays within 4 to 10 days after the initial detection of HIV-1 RNA. However, p24 antigen detection is transient because, as antibodies begin to develop, they bind to the p24 antigen and form immune complexes that interfere with p24 assay detection unless the assay includes steps to disrupt the antigen-antibody complexes.immunoglobulin (Ig)M antibodies are expressed which can be detected by 3rd and 4th generation immunoassays 3 to 5 days after p24 antigen is first detectable, 10 to 13 days after the appearance of viral RNA.
Finally, IgG antibodies emerge and persist throughout the course of HIV infection. First and second generation immunoassays designed to detect only IgG antibodies exhibit considerable variability in their sensitivity during early infection, becoming reactive 18 to 38 days or more after the initial detection of viral RNA.

Recommended Laboratory HIV Testing Algorithm for Serum or Plasma Specimens 

image
image

 FDA approved Tests

image

Source: Centers for Disease Control and Prevention (CDC); Read more


Get my updates delivered into your inbox; Privacy Policy :

Click here to Subscribe news feed from "Clinispot; so that you do not miss out anything that can be valuable to you !!

Related Posts with Thumbnails