What Is a Rapid HIV Test? How and When to Use It

Что важно знать об ифа-тестах?

У всех ИФА-тестов есть два серьезных недостатка. Во-первых, ИФА-тесты не определяют вирус ВИЧ сразу после инфицирования. Так происходит, потому что антитела к вирусу ВИЧ вырабатываются не сразу. Современные ИФА-тесты позволяют «засечь» иммунные белки только через 23—90 дней после заражения.

Во-вторых, ИФА-тесты на ВИЧ иногда дают ложноположительные результаты — то есть «находят» вирус ВИЧ у людей, у которых его на самом деле нет. Лабораторный ИФА-тест на ВИЧ может ошибаться так же, как и экспресс. Именно поэтому все положительные ИФА-тесты, как правило, подлежат проверке при помощи более надежных методов. В нашей стране с этой целью применяют вестерн-блоттинг.

Почему две полоски?

Принцип ИФА основан на реакции «антиген-антитело». У человека берут кровь или жидкость с десен (это не совсем слюна), в которой могут находиться антитела к вирусу ВИЧ.

Затем к ней добавляют реактив с белками вируса ВИЧ, а вернее, антигенами, но не простыми, а «доработанными». Антиген, который используют в реакции, отличается от обычного вирусного белка тем, что к нему «прицепили» химическую метку.

Пока «меченые» антигены плавают в реактиве сами по себе, ничего не происходит. Но если в биологической жидкости есть антитела к ВИЧ, то они соединятся с «мечеными» антигенами и дадут сигнал, который может засечь лаборант или экспресс-тест. Если антител к ВИЧ нет — сигнала не будет.

В экспресс-тестах, которые используются фондом СПИД.ЦЕНТР и многими другими нашими коллегами для бесплатного и анонимного тестирования, антитела тонкой линией нанесены на специальную поверхность, спрятанную под пластмассовым корпусом тестера.

Сначала клиент промокает десневую жидкость лопаточкой, установленной на конце тестера. А как только жидкость собрана, лаборант опускает лопаточку в реагент, который в течение 15 минут поднимается по тестеру, достигая в итоге полоски с антигенами.

Если антитела в десневой жидкости, смешанной с реагентом, были — полоска краснеет.

Как правило, на ручке тестера имеется и вторая полоса — контрольная, она окрашивается в красный всегда. Так что, как правило, отрицательный результат (вируса в организме нет) маркируется одной полоской на рукоятке тестера, а положительный (вирус в организме есть) — двумя.

Две полоски на тестере — это верный признак того, что человек некоторое время назад получил ВИЧ-инфекцию. А стало быть, клиенту срочно нужно обратиться к врачу за терапией — в областной или городской центр СПИД. Там ему будут назначены подтверждающие анализы и прописана антиретровирусная терапия.

Точно такой же тест (ИФА), только лабораторный, можно сделать и во многих коммерческих клиниках — но за деньги. Технология его в целом выглядит так же, а точность отличается незначительно.

Are hiv tests accurate?

Yes. Modern HIV tests are very accurate within the time limits that they are recommended.

A 4th generation HIV test (antigen/antibody) will detect 95% of infections at 28 days after exposure. It will detect 99% of infections at 6 weeks. At 3 months it will detect more than 99.99% of infections.

False negative results (where the test shows negative but you are actually HIV positive) are very rare from any blood test. They have been reported with some oral (saliva) tests if they are not given correctly. If you are worried about this, then a second will confirm whether the result is a test error.

A positive test result always needs to be routinely confirmed using a different type of test. When used as a confirmatory test this is close to 100% accurate.

If you are still worried, for example because of symptoms, then a viral load test will show if HIV is present. If the viral load test is negative, then the symptoms are not related to HIV.

Information about different types of tests

What is the difference between 3rd and 4th generation tests?

A few studies have suggested that 3rd generation testing might be accurate earlier than the explanation above.

Can i ask another person to test?

No. This is about your sexual health. It is your responsibility to test.

You have no right to impose your worries about your health on another person.

Only your status is important now. This involves taking responsibility for your own health.

Do i have hiv?

The only way for you to know this is to take an HIV test. Although websites can include information about different levels of risk, no website can answer whether or not you have HIV.

Information about different types of HIV tests.

This page includes information on how long you need to wait after any potential exposure for each type of test to be able to work.

Do i need to take a test if my partner just tested negative?

You can not use your partners test results to interpret your HIV status.

You can only know if you have HIV by taking your own test.

You could be HIV-positive and your partner has just been lucky so far. You need to know your status to protect your partner in the future.

If your partner has just tested HIV positive, you could still be HIV negative, even if you have had unprotected sex. You need your own test results.

Do i need to take an hiv test?

The only way you can know your HIV status by taking an HIV test. In the UK, 1 in 5 people (20%) who are HIV positive do not know their HIV status. In other countries this can be even higher.

Even if your exposure risk was low, you can only know whether you are HIV positive or HIV negative by taking a test.

An HIV test should be a routine part of looking after your sexual health. Repeating the test every 6-12 months is important in case you are exposed to HIV in the future. Some people are advised to test more frequently.

Information about different types of HIV tests.

Do i need to take another test?

No, not if your exposure risk was more than three months prior to the test.

If the test was taken less than three months after the exposure risk, then retesting three months after the exposure risk is recommended in most guidelines.

Does this symptom [… rash/itch/headache etc] related to hiv?

Most people worried about a recent infection mistake common symptoms of other illnesses with HIV. Stress and worry can cause and contribute to these symptoms. Information about symptoms of recent HIV infection.

If you have any symptoms that are worrying you, then seek medical advice from a doctor or other health care worker. The people working at i-Base are not doctors. We cannot diagnose HIV or any other illness.

How accurate is a test at 14, 18, 24, 27, 49, 100 days etc?

Test accuracy data based on 28 days. It is not available at other time points. Information on the i-Base website is based on 4th generation tests being 95% accurate at 4 weeks, and that this needs to be confirmed after three months with a second test. A negative text after three months (90 days) mean you are HIV negative.

• Testing earlier is less accurate, but can help if someone is anxious.
• Later testing later is more accurate, but involves a longer wait.

Test accuracy at different time points is difficult to estimate and study. It requires each type of HIV test being checked on blood samples from several hundred people who were donating blood frequently (usually twice a week) and who then became infected without realising it.

Only a small proportion of people regularly give blood and only a small proportion of those people catch HIV. These sample are difficult to get. Each manufacturer uses a similar bank of blood samples to estimate the sensitivity of their test.

Some samples show a positive result after only a week, others take several months. This is because of the wide range of individual responses to an infection.

How can my partner test positive and i test negative?

Why different people test positive and negative.

I am worried about taking an hiv test…

It is common to worry whenever you take a test.

If it turns out that you are HIV-positive, then it is better for you to know this as early as possible. You can then access appropriate monitoring and treatment. It will also help protect your sexual partners.

If it turns out that you are HIV-negative, then knowing this for certain will stop you worrying about this aspect of life.

An HIV test will focus you on your sexual health. If it is negative, use this experience to become aware of your sexual health in the futures. If you are sexually active, and take risks in the future, repeat the test every year as part of an annual check up.

Patient education

Provide frank, complete, nonjudgmental information on the routes of transmission. Teach HIV-infected patients how to minimize the risk to others.

For patient education information, see the Sexual Health Center, Rapid HIV Test, and HIV/AIDS.

For more information, see the CDC guidelines for HIV Infection: detection, counseling, and referral and revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings.

Ways you can not catch hiv

The following list includes examples or questions we get from people worried about catching HIV.

The information above should have clear enough these are not risks. Similar questions will not be answered in the Q&A pages but may just be added to this list below.

You can NOT catch HIV from:

• Masturbation
• Sexual activity with someone who does not have HIV
• Eating prepacked chicken which may have had human blood on it
• Eating any food cooked or uncooked with blood on it
• From a sterile needle at a GUM clinic or any other healthcare centre
• From a human bite
• From an insect bite including a mosquito bite
• From an animal
• From being in close proximity to a ‘sharps’ bin in a GUM clinic
• From living in the same house as someone who is HIV positive (unless you have unprotected sex)
• From a sewing needle if you stab your finger
• Blood on a bus seat that went through underwear
• Cleaning nail clippers
• Using a knife/fork/spoon/cup/plate etc
• From a plaster
• From a razor that hasn’t been used for hours (probably even minutes)
• From eating peanuts from a bowl

Last updated: 4 April 2020.

What about pep?

If you have have a recent high risk you can take a course of treatment called PEP. This stands for post exposure prophylaxis. PEP involves taking HIV medicines for a month.

PEP need to be started as soon as possible after an exposure, ideally within hours. It is unlikely to work after more than 48-72 hours.

Guidelines for testing for HIV are based on time since the PEP course is finished – ie 3-4 weeks after the end of PEP, with a confirmatory test 2 months after this.

More information about PEP.

What about rapid hiv tests?

Rapid HIV tests are 3rd generation tests. They only give an accurate result 8 weeks on longer after any risk.

What if my first test is positive and the second test is negative?

Please talk to your test centre doctor.

i-Base cannot interpret individual test results. This is something that your doctor or test centre has to do. The interpetation will depend on the type of test, your risk, and the time between the risk and testing.

Usually the second test will be the accurate result – but this is something to talk the doctor or clinic about.

What is my risk for having caught hiv?

We get many questions about different risks and the likelihood of having caught HIV.

HIV is mainly transmitted sexually and by sharing drug-using equipment. HIV is infectious in blood, semen, vaginal fluid and breastmilk. However, these fluids do not remain infectious for very long outside the body. Most studies suggests that within a minute or two HIV is no longer infectious in these fluids.

HIV is not transmitted by everyday contact or from contact with objects that an HIV-positive person has touched. HIV is not transmitted by saliva, sweat, spit, urine or faeces. Tears may contain HIV but this is unlikely to be a practical route of transmission.

HIV is not transmitted by deep-kissing, or from body rubbing or contact with infectious fluid on skin. HIV is not spread by air or by insects.

You can catch HIV by having sex without a condom – if you are not taking PrEP or the positive person is not on treatment (see Treatment as Prevention).

If you have had sex without a condom with someone who might be HIV positive, then this is a risk for HIV. However, one single time, this risk is likely to be very low. For example, depending on the type of sex this might be as low as from 1 in 100 to 1 in 500.

If the HIV positive person is on effective treatment, this risk is zero.

The the HIV negative person is taking PrEP, this risk it likely to be effectively zero.

The highest risk is if someone doesn’t know they are HIV positive, perhaps because this was a recent infection. In early infection, viral load can be very high. This make a person more infectious.

Information about how HIV is transmitted from AVERT.

Learn about HIV transmission from the above web link.

• If you think you may have HIV, or have been at risk of catching HIV then seek medical advice and take an HIV test.
• i-Base does not answer questions on individual risk of catching HIV.
• Testing is easy and cheap or free. If you are worried that you have been at risk, like millions of other people, take a test.

What is seroconversion? what are the symptoms?

Information on seroconversion.

What is the risk if the hiv positive person is on treatment?

HIV treatment dramatically reduces the risk of HIV transmission.

If the HIV positive person has an undetectable viral load on treatment (less than 50 copies/mL) this becomes zero.

Viral load and risk of transmission.

The PARTNER1 study reported ZERO HIV transmission after more than 58,000 times when HIV positive people with undetectable viral load had sex WITHOUT using condoms. The PARTNER2 study reported ZERO transmission in gay couples after approximately 77,000 times that gay couple had sex without condoms.

Q & A on the partner study.

When can i take a test?

How soon after exposure you test depends on your risk of exposure and which tests you can use. See the link above.

In 2020 UK guidelines changed. They now say that 4th generation HIV tests (antigen/antibody) will detect 99% of infections 6 weeks after exposure. This is good enough to not need a second test.

Previous guidelines used to say 95% of cases will be picked up by 4 weeks. A negative result at 4 weeks though needs to be confirmed with a second test three months later. This is to pick up the 5% of people who take longer to generate an immune response.

In high risk exposures (ie needlestick injury by a health care worker with known HIV-positive person), especially if symptoms occur, then viral load testing is sometimes used after one week.

Where can i get an hiv test in the uk?

Where to get an HIV test in the UK?.

Where can i get more information about risks of catching hiv?

This online guide has a lot more infromation about different risks.

Which test can i use?

In the UK, a 4th generation antigen/antibody test used to be easy to get 3-4 weeks after an exposure risk. A second test three months after the risk was then needed to pick up the small percentage of people who take up to three months to develop an antibody response. The three month test can be a 3rd or 4th generation test. HIV testing is free in the UK and most other countries.

However, as mentioned above, UK guidelines now want people to wait six weeks to have a single test. If you do this there is then no need to have a second confirmatory test.

Viral load test are not approved or recommended for diagnosing HIV. They are sometimes used in specific circumstances after a recent high level risk especially if there are symptoms consistent with seroconversion.

Routinely using viral load tests to try to get a quicker answer to whether you have been infected is not recommended. They are not accurate for this. Although some private clinics offer them for this use, they will not accurately answer the question of whether you have been infected.

Information about different types of tests.

Why do i need another test at 3 months after an exposure?

Please follow this link for a very comprehensive answer regarding the BASHH guidelines and why it is that some GUM clinics still ask patients to do a confirmatory test at 3 months.

Why do some doctors (and websites) say to test again at 6 months?

We are based in the UK and our information is based on UK guidelines. There are occasional reports where people may take longer than three months to develop antibodies to HIV. If they occur these are very rare.

A negative test at three months means it is fine to get on with your life. The experience of taking an HIV test should help focus you on taking fewer risks in the future. It should also make it easier to routinely include an HIV test in your future sexual health care.

Whether this is after six months or every year will depend on how often you have sex that includes the risk of HIV.

Testing is usually free and easy. You will not do any harm if you want to test at six months. Just don’t spend the time obsessing over HIV because a negative test at three months is very good news!

Will i be positive if i slept with an hiv positive person without a condom?

HIV is a difficult virus to catch sexually.

Even if your partner is HIV positive and you did not use a condom, the risk is usually less than 1 in 100 (less than 1%). This might be less than 1 in 500.

However, it only takes one exposure to catch HIV. This means that luck and other factors are involved.

So out of thousands of people who have a risk of catching HIV, some will become positive. For some people this might be from their first risky exposure.

HIV is therefore generally a low risk event, but with potentially serious outcomes. Taking an HIV testing to know your HIV status is a good idea.

Guide to HIV transmission and testing.

Will pep work as prep?

PrEP is a different way of using HIV meds to protect against HIV infection.

It involves taking a combination pill of two HIV meds. This is usually tenofovir (TD or TAF) plus emtricitabine (FTC). PrEP is either taken as a single pill every day (by cis women and trans men and women) or as needed (by cis men).

Technically, if your PEP includes TD/FTC if will work as daily PrEP for everyone for the middle two weeks. For cis men, TD/FTC will work as PrEP from about day 4 to about day 26.

More information on PrEP.

UK guide to PrEP.

В чем проблема с российскими анализами на вич?

В нашей стране для подтверждения ВИЧ-статуса используют лабораторный ИФА-тест и вестерн-блоттинг — это стандартная процедура. Однако Всемирная организация здравоохранения (ВОЗ) отмечает: в странах, где действует эта схема, на определение ВИЧ-статуса тратится очень много времени и средств. Причем ожидание результата настолько изматывает, что некоторые пациенты даже жалеют о решении узнать свой ВИЧ-статус.

Эксперты ВОЗ советуют отказаться от лабораторных ИФА-тестов и вестерн-блоттинга в пользу комбинированных экспресс-тестов, которые дают быстрый и более надежный результат. И это действительно работает.

Например, в США от «подтверждающего» инфекцию вестерн-блоттинга в принципе отказались. И для определения, и для подтверждения ВИЧ-статуса в этой стране используют комбинированные лабораторные и экспресс-тесты. Это не только дешевле для государства, но и психологически проще для людей: поскольку время ожидания меньше, а сама процедура — проще, все больше американцев вовремя узнают свой ВИЧ-статус и начинают своевременное лечение.

Какие бывают тесты ифа?

●        «Домашний» экспресс-тест — OraQuick HIV ½ Rapid Antibody Test. Материал для теста — жидкость, которую собирают с десен специальной мягкой щеточкой. Тест выдает результат очень быстро: в течение 20 минут.

●        Лабораторный ИФА-тест — анализ на ВИЧ по форме 50. В нашей стране его применяют в качестве стандартной процедуры лабораторной диагностики ВИЧ-инфекции. Материал для анализа — кровь из вены, которую нужно сдавать в лаборатории. Результаты приходят через 1—5 дней.

Коротко о вирусе вич и ифа

Все анализы на ВИЧ предназначены для того, чтобы либо разыскать части вируса, либо зафиксировать реакцию организма на его присутствие. Поэтому, чтобы понять, как работают тесты на ВИЧ, нужно примерно представлять, как устроен вирус и как он себя ведет, оказавшись в клетке.

Вирус ВИЧ — член семейства ретровирусов (Retroviridae). Представители этого семейства выглядят как крохотные круглые частицы, у которых есть оболочка, усеянная особыми белками. При помощи этих белков вирус распознает клетку-жертву и прикрепляется к ней.

Затем оболочки клетки и вируса сливаются, а внутрь клетки попадает содержимое вируса — нуклеокапсид. Нуклеокапсид — это белковая капсула, внутри которой находятся генетическая информация об устройстве вируса — две копии двухцепочечной РНК — и набор ферментов, которые «включают» РНК, когда та окажется в клетке.

Тестов на ВИЧ очень много, но их можно разделить на несколько больших типов. Те экспресс-тесты, которыми пользуются большинство ВИЧ-сервисных НКО, устроены по принципу иммуноферментного анализа, или ИФА.

Их задача — определить антитела к ВИЧ, которые организм вырабатывает в ответ на проникновение в него вируса.

Как это работает? Когда вирус ВИЧ попадает в организм, иммунная система человека не сидит без дела. Она начинает продуцировать антитела — иммунные белки, которые помогают организму бороться с инфекцией. Эти белки можно обнаружить во многих биологических жидкостях.

Способов обнаружения таких антител существует много. Но наиболее популярным считается именно иммуноферментный анализ (ИФА). За рубежом этот тест называется enzyme-linked immunosorbent assay, сокращенно — ELISA.

Подтверждающие тесты: вестерн-блоттинг (wb)

Цель этого теста — подтвердить результаты первичного анализа.

Вестерн-блоттинг можно провести только в лаборатории. Такие тесты не бывают «карманными», именно поэтому все НКО, которые тестируют граждан на ВИЧ, в итоге отправляют своих клиентов в лаборатории центров СПИД сдавать именно этот анализ, если экспресс-тестер показал положительный результат.

Вестерн-блоттинг (или иммуноблот) по технологии — тот же ИФА-анализ, основанный на реакции «антиген-антитело», только очень точный, долгий и кропотливый.

Чтобы провести анализ, у человека берут кровь и добывают из нее сыворотку. Это все та же кровь, только без эритроцитов, иммунных клеток и всего остального, что может образовывать сгустки крови. Потом эту сыворотку наносят на полоску из нитроцеллюлозы, на которой в строгом порядке размещены различные антигены ВИЧ — белки из оболочки и нуклеокапсида вируса. Если в сыворотке крови уже успели появиться антитела, они свяжутся с антигенами, размещенными на полоске.

Потом к смеси добавляют новый реактив-«проявитель». Как и в фотографии, этот реактив нужен, чтобы понять, прошла реакция или нет. В реактиве-«проявителе» находятся антитела, помеченные химической меткой. Но это антитела не к антигенам вируса ВИЧ, а к человеческим антителам, которые умеют связываться с комплексом «антиген-антитело».

Если в образце есть комплекс «антиген-антитело», на полоске проявятся окрашенные полосы. Каждая полоска означает свой вирусный белок. Реакция считается очень точной — в большинстве случаев вестерн-блоттинг позволяет исключить случайное срабатывание теста.

Какие бывают тесты этого типа? Разные. Некоторые позволяют подтвердить наличие вируса ВИЧ-1, некоторые — ВИЧ-2, а некоторые — обоих вариантов вируса сразу.

Пример: российская тест-система ИФА-Лайн-Блот-ВИЧ-1,2. Эта тест-система участвует в тендерах — закупках в государственные лаборатории, которые действуют при СПИД-центрах.

Пцр: самый сложный анализ

Тесты, позволяющие определить непосредственно генетический материал вируса ВИЧ, называются полимеразной цепной реакцией с обратной транскрипцией (ПЦР-ОТ).

Методов полимеразной цепной реакции (ПЦР), при помощи которой можно определять вирус ВИЧ, существует много. Но понять, что именно происходит в пробирке, проще всего на примере ПЦР с обратной транскрипцией (ПЦР-ОТ).

Экспресс-тесты на вич: какие лучше и насколько они правдивы

How are results given?

Your test centre should clearly explain the results of your test.

If you have questions that we not explained, or that still worry you, go back to ask that centre again.

Results are generally given as:

• Negative / non-reactive = HIV-negative = You do not have HIV (based on the window period and assuming you have not had any more recent risks)
• Positive / reactive = HIV-positive = You have HIV infection
• Indeterminate = the test results was unclear and will be checked with another test

What is a ‘false positive’ test result?

A false positive test is when the test result shows positive but the person is negative.

This can happen with antibody tests when the test picks up antibodies for other infections.

Approximately 15 out of every 1000 antibody tests are a false positive (1.5%).

The fourth generation tests have a much lower chance of a false positive. This is why you should always have a second confirmatory test if the result is positive.

The test used to confirm a positive result is 100% accurate. If the second test does not confirm you are positive then you do not have HIV.

What is a ‘false negative’ test result?

A false negative test result occurs when the test shows negative and the person is really HIV positive.

This is very rare. It usually occurs during the window period when someone is very recently infected but the test can’t pick up the infection.

Nearly all tests have a margin of error. this is usually small. With HIV antibody tests only 0.3% of tests (3 tests in every 1000) will be a false negative after 3 months.

With fourth generation tests, it is lower still at 3 months.

If you are worried you can take a second test. This will eliminate the possibility of a false negative result.

Is a negative result 100% accurate?

We get asked this a lot. As an information service we have to say that technically, no test is 100% accurate.

This is partly to do with language. In science you can never prove 100% that something is NOT there or that something will NEVER happen. This is referred to as “the impossibility of proving a negative”.

In practice, a negative result three months after your last exposure risk is interpreted to mean you do NOT have HIV.

In real life, this means you do NOT have HIV.

If you have symptoms, this is not likely to be due to HIV. If they were related to HIV you would test positive. The symptoms are related to something else – see a doctor.

Does a negative result mean i do not have hiv? is the result conclusive?

Yes if the test was three months after your exposure risk. This is the purpose to testing. If the result is negative, and you have not had another risk, you do not have HIV. Stop worrying. Learn from the experience you have gone through taking a test. Learn about how to protect yourself. Look after your sexual health in the future.

If your test was less than three months after the exposure then you might need to test again after three months. This depends on your risk.

If you tested negative four weeks after the exposure, you a very likely to be HIV-negative. In the UK, whether or not you need to confirm the result with a second test several months later depends on your risk. This is because 5% of people can take longer than four weeks to generate an immune response.

Can meds or other things affect the result of my hiv test?

HIV antibody tests are not affected by other infections, medications, vaccinations, putting on weight, eating or drinking anything before the test, use of alcohol or recreational drugs, mouthwash or time of day.

Your test result is accurate even if you had flu or a cold or are using antihistamine treatment, for example, for hay fever.

You do not need to fast before your test, eating and drinking before the test will not affect the results.

What does a number on my negative hiv test result mean?

The number (ie 0.06 or 0.64 etc) is a more accurate (quantitative) way of measuring the result other than a simple, yes or no.

• If the number is less than 1.0 the result is negative.
• if the result is above 1.0 the result is positive
• If the result is very close to 1.0 then the doctor may decide a confirmatory test is required.

The number means nothing else in itself. A result of 0.3 does not mean you are more likely to become positive than a number of 0.03. Increasing numbers with several test does not mean you are more likely to be positive.

The graphic below is an example of this sort of test result.