What are my HIV test­ing op­tions?

Next combo tests of­fer faster, more re­li­able re­sults

Tehran Times - - HEALTH - (Source: very­well.com) By Den­nis Sifris

When an HIV in­fec­tion is sus­pected, it is most com­monly di­ag­nosed by tests that can de­tect cells called an­ti­bod­ies and/or anti­gens in ei­ther the blood or saliva.

An an­ti­body is a type of pro­tein se­creted by white blood cells that can de­tect and de­stroy for­eign bod­ies like viruses or bac­te­ria. An anti­gen, by con­trast, is any sub­stance that can pro­voke an im­mune re­sponse in the form of an­ti­bod­ies (as hap­pens with HIV).

The tests used to con­firm HIV in­fec­tion are de­signed to re­act with th­ese agents. A “pos­i­tive” re­sult means that HIV an­ti­bod­ies/anti­gens have been de­tected and that an in­fec­tion has oc­curred. A “neg­a­tive” re­sult means that no an­ti­bod­ies/anti­gens have been de­tected and that HIV in­fec­tion has not oc­curred.

Con­versely, a “false pos­i­tive” is when a test in­cor­rectly in­di­cates an HIV in­fec­tion, while a “false neg­a­tive” is when the test in­cor­rectly shows that no in­fec­tion has oc­curred. Both of th­ese are rel­a­tively rare are us­ing cur­rent test­ing as­says.

Un­der­stand­ing the win­dow pe­riod

Peo­ple will usu­ally de­velop mea­sur­able lev­els of HIV an­ti­bod­ies within 30 days of in­fec­tion, al­though some may take longer—up to three months in some cases. HIV anti­gens, by con­trast, take be­tween two to five weeks to de­velop.

Be­fore this hap­pens, there is a pe­riod wherein an­ti­body/anti­gen lev­els are too low to be re­li­ably de­tected.

This is called the win­dow pe­riod. It is dur­ing this time that an in­fected per­son can pass HIV to oth­ers, but still have a neg­a­tive re­sult if given an HIV test.

If you be­lieve you have been in­fected and sus­pect when you might have been ac­ci­den­tally ex­posed to HIV, it’s im­por­tant that you share this with your doc­tor or test­ing cen­ter.

They can then help de­ter­mine if the HIV test falls within the win­dow pe­riod or if it can be per­formed with rea­son­able lev­els of re­li­a­bil­ity.

HIV an­ti­body tests

The HIV ELISA (en­zyme-linked im­munosor­bent as­say) is a highly sen­si­tive test that changes color when HIV an­ti­bod­ies are present. Re­sults are as­signed a nu­meric value, with val­ues be­low 1.0 in­di­cat­ing a neg­a­tive re­sult and val­ues above 1.0 in­di­cat­ing a pos­i­tive (or re­ac­tive) re­sult. Al­though the ELISA of­fers a high prob­a­bil­ity of HIV in­fec­tion, it is not used alone as in the de­tec­tion of HIV.

When an ELISA test pro­duces a pos­i­tive re­sult, a sec­ond an­ti­body test, called the Western Blot, is used to con­firm the re­sults. To­gether, the ELISA and Western Blot are shown to have an ac­cu­racy of 99.9 per­cent in the gen­eral U.S. pop­u­la­tion, with a false-pos­i­tive rate of about one out of ev­ery 250,000 tests per­formed.

Oc­ca­sion­ally, the tests can re­turn with an in­de­ter­mi­nate or in­con­clu­sive re­sult. This can hap­pen for a num­ber of

rea­sons:

The in­fec­tion may have been too re­cent to re­li­ably de­tect.

There may have been prob­lems with the test sam­ple or the test­ing pro­ce­dure it­self.

Acute in­fec­tions like syphilis ?or Lyme’s dis­ease can some­times elicit a false pos­i­tive re­sult, as can au­toim­mune con­di­tions like lu­pus or di­a­betes.

If a per­son has an in­con­clu­sive re­sult, the tests should be re­peated.

Com­bi­na­tion anti­gen/an­ti­body tests

On June 27, 2014, the Cen­ters for Dis­ease Con­trol and Preven­tion rec­om­mended a new strategy for HIV test­ing us­ing 4th gen­er­a­tion com­bi­na­tion as­says. Th­ese next gen­er­a­tion tests are able to test for both HIV an­ti­bod­ies (Ab) and anti­gens (Ag) and can con­firm an HIV in­fec­tion up to four weeks ear­lier than ELISA/Western Blot as­says.

There are two such tests ap­proved by the U.S. Food and Drug Ad­min­is­tra­tion for use in HIV screen­ing: the Alere De­ter­mine HIV 1/2 Ag/Ab Combo and the Ab­bott AR­CHI­TECT HIV Ag/Ab Combo.

Based on their high level of test­ing ac­cu­racy, the CDC rec­om­mends the fol­low­ing three-step ap­proach:

Conduct ini­tial test­ing with Ag/Ab combo as­says. If the re­sult is neg­a­tive, then no fur­ther test­ing is needed.

If the first re­sult is pos­i­tive, conduct a sec­ond test to dif­fer­en­ti­ate HIV-1 and HIV-2 an­ti­bod­ies, a step con­sid­ered im­por­tant in de­ter­min­ing the course of ther­apy for the HIV-in­fected in­di­vid­ual.

If the sec­ond re­sult is neg­a­tive, a third test (called the HIV-1 NAT) would be per­formed to dif­fer­en­ti­ate acute HIV1 in­fec­tion from an ini­tial false pos­i­tive re­sult. The HIV-1 NAT is able to de­tect small quan­ti­ties of viral RNA is as lit­tle as one to two weeks.

Due to the re­li­able com­bi­na­tion of Ag/Ab test­ing, con­fir­ma­tion by way of a Western Blot is no longer con­sid­ered nec­es­sary.

Rapid in-home HIV tests

Rapid in-home HIV tests are ELISAbased as­says that can de­liver re­sults in as a lit­tle as 20 min­utes (as op­posed to stan­dard ELISA/Western Blot as­says that can take sev­eral days). The tests are per­formed us­ing saliva sam­ples, the re­sults of which can ei­ther be “neg­a­tive” or “pre­lim­i­nary pos­i­tive.” Pre­lim­i­nary pos­i­tives must be con­firmed with a Western Blot per­formed in a lab.

In 2012, the FDA ap­proved the first in-home rapid HIV test for di­rect sale to con­sumers. While the prod­ucts are easy to use and of­fer link­age to care for those who do test pos­i­tive (via a 24-hour con­sumer hot­line), some are con­cerned that the lack of face-to-face coun­sel­ing and po­ten­tial breaches in in­formed con­sent may un­der­mine preven­tion ef­forts.

Fur­ther­more, while the in-home tests of­fer the same sen­si­tiv­ity and speci­ficity as point-of-care tests, clin­i­cal re­search has demon­strated a false neg­a­tive rate of around seven per­cent (or roughly one out of 12 tests).

An­other study pub­lished by the Univer­sity of Cal­i­for­nia, San Fran­cisco has sug­gested that fourth gen­er­a­tion rapid tests have a real-world ac­cu­racy of around 86 per­cent in cor­rectly iden­ti­fy­ing HIV-pos­i­tive cases but only 54 per­cent ac­cu­racy in con­firm­ing serosta­tus dur­ing the early, acute stages of HIV in­fec­tion.

With mount­ing ev­i­dence sug­gest­ing that early di­ag­no­sis and treat­ment may pre­vent a num­ber of long-term com­pli­ca­tions — in­clud­ing a pos­si­ble re­duc­tion in the viral reser­voirs where HIV can per­sist for decades — the need for ac­cu­rate iden­ti­fi­ca­tion dur­ing acute in­fec­tion is con­sid­ered im­per­a­tive.

The win­dow pe­riod is the time that an in­fected per­son can pass HIV to oth­ers, but still have a neg­a­tive re­sult if given an HIV test.

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