Editing HIV (section)

== Diagnosis ==
{{Main|Diagnosis of HIV/AIDS}}
[[File:Hiv-timecourse copy.svg|upright=1.35|thumb|right|A generalized graph of the relationship between HIV copies (viral load) and CD4 counts over the average course of untreated HIV infection; any particular individual's disease course may vary considerably. {{legend-line|blue solid 2px|CD4<sup>+</sup> T cell count (cells per µL)}} {{legend-line|red solid 2px|HIV RNA copies per&nbsp;mL of plasma}}]]

Many HIV-positive people are unaware that they are infected with the virus.<ref name="Kumaranayake">

{{cite journal | vauthors = Kumaranayake L, Watts C | title = Resource allocation and priority setting of HIV/AIDS interventions: addressing the generalized epidemic in sub-Saharan Africa | journal = Journal of International Development | year = 2001 | pages = 451–466 | volume = 13 | issue = 4 | doi = 10.1002/jid.797}}</ref> For example, in 2001 less than 1% of the sexually active urban population in Africa had been tested, and this proportion is even lower in rural populations.<ref name="Kumaranayake" /> Furthermore, in 2001 only 0.5% of [[Pregnancy|pregnant women]] attending urban health facilities were counselled, tested or received their test results.<ref name="Kumaranayake" /> Again, this proportion is even lower in rural health facilities.<ref name="Kumaranayake" /> Since donors may therefore be unaware of their infection, [[Blood donation|donor blood]] and blood products used in medicine and [[medical research]] are routinely screened for HIV.<ref name="Kleinman">{{cite web | author=Kleinman S | publisher=Uptodate | date=September 2004 | url=http://www.uptodate.com/patients/content/topic.do?topicKey=blod_dis/2419 | title=Patient information: Blood donation and transfusion | archive-url=https://web.archive.org/web/20080412115832/http://www.uptodate.com/patients/content/topic.do?topicKey=blod_dis%2F2419 | archive-date=April 12, 2008 | url-status=dead | df=mdy-all }}</ref>

HIV-1 testing is initially done using an [[enzyme-linked immunosorbent assay]] (ELISA) to detect antibodies to HIV-1. Specimens with a non-reactive result from the initial ELISA are considered HIV-negative, unless new exposure to an infected partner or partner of unknown HIV status has occurred. Specimens with a reactive ELISA result are retested in duplicate.<ref name="CDC2001">{{cite journal |author=Centers for Disease Control and Prevention | title = Revised guidelines for HIV counseling, testing, and referral | journal = MMWR Recommendations and Reports | volume = 50 | issue = RR–19 | pages = 1–57 | year = 2001 | pmid = 11718472 }}</ref> If the result of either duplicate test is reactive, the specimen is reported as repeatedly reactive and undergoes confirmatory testing with a more specific supplemental test (e.g., a [[polymerase chain reaction]] (PCR), [[western blot]] or, less commonly, an [[immunofluorescence assay]] (IFA)). Only specimens that are repeatedly reactive by ELISA and positive by IFA or PCR or reactive by western blot are considered HIV-positive and indicative of HIV infection. Specimens that are repeatedly ELISA-reactive occasionally provide an indeterminate western blot result, which may be either an incomplete antibody response to HIV in an infected person or nonspecific reactions in an uninfected person.<ref name="celum">{{cite journal | vauthors = Celum CL, Coombs RW, Lafferty W, Inui TS, Louie PH, Gates CA, McCreedy BJ, Egan R, Grove T, Alexander S | title = Indeterminate human immunodeficiency virus type 1 western blots: seroconversion risk, specificity of supplemental tests, and an algorithm for evaluation | journal = The Journal of Infectious Diseases | volume = 164 | issue = 4 | pages = 656–664 | year = 1991 | pmid = 1894929 | doi = 10.1093/infdis/164.4.656 }}</ref>

{{Pie chart
 | caption= HIV deaths in 2014 excluding the U.S.:<ref>{{cite web |title=Country Comparison :: HIV/AIDS - Deaths |url=https://www.cia.gov/library/publications/the-world-factbook/rankorder/2157rank.html |publisher=The World Factbook, Central Intelligence Agency |access-date=November 22, 2015 |archive-date=April 30, 2017 |archive-url=https://web.archive.org/web/20170430003645/https://www.cia.gov/library/publications/the-world-factbook/rankorder/2157rank.html |url-status=dead }}</ref>
 | other = yes | color = cyan
 | label1 = [[Nigeria]] | value1 = 15.76
 | color1 = silver
 | label2 = [[South Africa]] | value2 = 12.51
 | color2 = #FF0000
 | label3 = [[India]] | value3 = 11.50
 | color3 = #800080
 | label4 = [[Tanzania]] | value4 = 4.169
 | color4 = #008000
 | label5 = [[Mozambique]] | value5 = 4.061
 | color5 = #00058f
 | label6 = [[Zimbabwe]] | value6 = 3.49
 | color6 = #808000
 | label7 = [[Cameroon]] | value7 = 3.09
 | color7 = #7953c1
 | label8= [[Indonesia]] | value8 = 3.04
 | color8 = #FFA500
 | label9= [[Kenya]] | value9 = 2.98
 | color9 = #704045
 | label10= [[Uganda]] | value10 = 2.97
 | color10 = #536cb6
 | label11 = [[Malawi]] | value11 = 2.94
 | color11 = #5d2e68
 | label12 = [[Democratic Republic of the Congo|DR Congo]] | value12 = 2.17
 | color12 = #add2d5
 | label13 = [[Ethiopia]] | value13 = 2.11
 | color13 = #033e88
}}

Although IFA can be used to confirm infection in these ambiguous cases, this assay is not widely used. In general, a second specimen should be collected more than a month later and retested for persons with indeterminate western blot results. Although much less commonly available, [[nucleic acid test]]ing (e.g., viral RNA or proviral DNA amplification method) can also help diagnosis in certain situations.<ref name="CDC2001" /> In addition, a few tested specimens might provide inconclusive results because of a low quantity specimen. In these situations, a second specimen is collected and tested for HIV infection.

Modern HIV testing is extremely accurate, when the [[window period]] is taken into consideration. A single screening test is correct more than 99% of the time.<ref>{{cite journal | vauthors = Chou R, Selph S, Dana T, Bougatsos C, Zakher B, Blazina I, Korthuis PT | title = Screening for HIV: systematic review to update the 2005 U.S. Preventive Services Task Force recommendation |s2cid-access=free |doi-access=free | journal = Annals of Internal Medicine | volume = 157 | issue = 10 | pages = 706–18 | date = November 2012 | pmid = 23165662 | doi = 10.7326/0003-4819-157-10-201211200-00007 | s2cid = 27494096 }}</ref> The chance of a false-positive result in a standard two-step testing protocol is estimated to be about 1 in 250,000 in a low risk population.<ref name="ScreenReview2005">{{cite journal | vauthors = Chou R, Huffman LH, Fu R, Smits AK, Korthuis PT | title = Screening for HIV: a review of the evidence for the U.S. Preventive Services Task Force |s2cid-access=free |doi-access=free | journal = Annals of Internal Medicine | volume = 143 | issue = 1 | pages = 55–73 | date = July 2005 | pmid = 15998755 | doi = 10.7326/0003-4819-143-1-200507050-00010 | author6 = US Preventive Services Task Force | s2cid = 24086322 }}</ref> Testing post-exposure is recommended immediately and then at six weeks, three months, and six months.<ref name="PEP10">{{cite journal | vauthors = Tolle MA, Schwarzwald HL | title = Postexposure prophylaxis against human immunodeficiency virus |url=https://www.aafp.org/pubs/afp/issues/2010/0715/p161.html | journal = American Family Physician | volume = 82 | issue = 2 | pages = 161–6 | date = July 2010 | pmid = 20642270 |url-status=live |archive-url=https://web.archive.org/web/20231128140702/https://www.aafp.org/pubs/afp/issues/2010/0715/p161.html |archive-date= Nov 28, 2023 }}</ref>

The latest recommendations of the US [[Centers for Disease Control and Prevention (CDC)|Centers for Disease Control and Prevention]] (CDC) show that HIV testing must start with an [[immunoassay]] combination test for HIV-1 and HIV-2 [[Antibody|antibodies]] and p24 [[antigen]]. A negative result rules out HIV exposure, while a positive one must be followed by an HIV-1/2 antibody differentiation immunoassay to detect which antibodies are present. This gives rise to four possible scenarios:
* 1. HIV-1 (+) & HIV-2 (−): HIV-1 antibodies detected
* 2. HIV-1 (−) & HIV-2 (+): HIV-2 antibodies detected
* 3. HIV-1 (+) & HIV-2 (+): both HIV-1 and HIV-2 antibodies detected
* 4. HIV-1 (−) or indeterminate & HIV-2 (−): [[Nucleic acid test]] must be carried out to detect the acute infection of HIV-1 or its absence.<ref name="cdc.gov">{{cite web|title=Quick Reference Guide—Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations|url=https://www.cdc.gov/hiv/pdf/testingHIValgorithmQuickRef.pdf|website=Centers for Disease Control and Prevention |publisher=New York State Department of Health|access-date=April 13, 2017|pages=1–2|date=June 27, 2014|archive-url=https://web.archive.org/web/20170302175531/https://www.cdc.gov/hiv/pdf/testingHIValgorithmQuickRef.pdf|archive-date=March 2, 2017|url-status=dead}}</ref>