How Herpes Is Diagnosed

Herpes simplex virus (HSV) types 1 and 2 infections can be diagnosed based on the appearance of lesions (if present), as well as with laboratory tests. In general, though, if you do not have symptoms, there is no need for you to have any diagnostic testing for HSV type 1, which causes cold sores. If you may have been exposed to HSV type 2, a sexually transmitted disease that causes genital sores, you may need to be tested even if you do not have lesions.

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Both HSV-1 and HSV-2 can cause visible skin lesions. Because such lesions can also be the result of other illnesses, it is really important that you see a doctor, especially if you've never had an outbreak before. Once you've had herpes, you can learn to recognize the lesions in case you experience recurrences. But if you have worse recurrences or if the lesions look different than usual, then you should see a doctor. 

Herpes outbreaks usually appear as one or more blisters in clusters. The blisters may break open to become sores.

Cold sores are usually caused by HSV 1, and genital herpes infections are usually caused by HSV 2. However, either virus can infect either location.

If you or your child experiences pain or tingling around or inside the mouth or on the tongue, you can feel and look for bumps and blisters around the painful area, which may indicate HSV-1.

If you have pain in or around the genital area, or if you have pain with urination or sexual activity, look for redness, swelling, sores, or blisters in or around the affected area, which may indicate HSV-2. Know, though, that genital herpes infections are often asymptomatic. You should check for lesions if you think you could have been exposed to the infection. 

Labs and Tests 

If you have symptoms of HSV type 1 or 2, your doctor can diagnose a herpes infection by looking at your skin and/or by swabbing the sores to test for evidence of the herpes virus. If you do not have obvious symptoms, a blood test can help determine whether you have an infection. 

Swab Testing

The gold standard for herpes diagnosis is a viral culture test or nucleic acid amplification test (NAT) of a sample of skin, crust, or fluid from the lesion, which is usually obtained with a gentle swab of the area.

A viral culture is a test that allows the virus to grow in a laboratory setting. The NAT tests for the genetic material of the virus in the sample. These tests should only come back positive if you have the virus present in the lesion. In general, the results of the test are reliable (not a high chance of false positives or false negatives) and if you have active lesions, you do not need to wait any specified period of time to have the test.  

Herpes Blood Tests

It is possible to screen for asymptomatic herpes infections using a blood test. Herpes blood tests look for antibodies to the herpes virus.

You form antibodies when you need to fight an infection, and antibodies can last for years or even a lifetime. Generally, it takes about two weeks for your body to produce detectable antibodies against herpes virus infection. The presence of antibodies is evidence that your body has confronted an infection, either recently or in the past.

If you have a reinfection, antibody tests are not helpful because once you have the antibodies, they stay in your blood even when the virus becomes dormant. 

There are two kinds of blood tests for herpes:

  • Type-specific herpes blood tests look for not only whether you have antibodies against a herpes virus, but also for whether the antibodies are against HSV-1 or HSV-2. Type-specific testing will not tell you where your herpes infection is located in your body.
  • General herpes blood tests look only for whether you have antibodies against any type of herpes, and they do not specify whether you have antibodies to HSV-1 or HSV-2.

There are several different brands of blood tests that are used to detect viral proteins, and there are pros and cons for each. It is difficult to know how long it takes for blood tests to become positive after infection with HSV-1. The median time from the onset of symptoms to a positive HSV-2 blood test is as follows:

  • HerpeSelect ELISA: 3 weeks 
  • Western blot: 1 to 3 months 
  • Kalon ELISA: 120 days
  • Focus ELISA: 21 days 

In general, it usually takes around two weeks for symptoms to appear after you have been infected with HSV type 1 or 2. If you do not have lesions that can be swab tested, it is a good idea to wait at least a month or two before getting an HSV-2 test after a potential exposure. This is because it takes time for your body to make antibodies that can be detected in the blood. Testing before these antibodies are present can lead to a false-negative result.

There is also some possibility that herpes blood tests may detect antibodies to similar viruses through cross-reaction. This result would lead to a false-positive result, suggesting you have the infection when you don't.

If you have a strong reason to believe that you have been infected, you might want to consider getting retested after six months because some of the tests take longer to become positive.

In Newborns

The diagnosis of neonatal herpes is challenging. Generally, babies are not screened for herpes infection. Symptoms such as lesions around the mouth or eye may alert caregivers that there is a problem. This should prompt diagnostic testing, which can be done using a swab sample. However, more complicated neonatal herpes infections, such as encephalitis (infection of the brain), require more specific tests such as a lumbar puncture.  

Differential Diagnoses

There are a few other conditions that can be confused with cold sores or genital herpes. Some of these conditions are quite serious, and it is not safe for you to self-diagnose. Typically, these conditions can be distinguished from herpes with a medical examination or with laboratory tests.  

  • Canker sores: Canker sores are usually red, raised sores with a painful, raw, whitish pit in the center. They may be present in the mouth, and they tend to occur as a result of oral trauma. The initial painful sensation of canker sores and cold sores is similar, but the lesions look different, and canker sores do not test positive for herpes simplex virus. 
  • Syphilis: A sexually transmitted disease that produces painless genital sores, syphilis can be confused with herpes. Your doctor may be able to tell the difference by visually inspecting the lesions. If you have syphilis, your blood tests should be positive for Treponema pallidum, the bacteria that causes syphilis infection; they would be positive for HSV if herpes is the cause of your genital lesions. 
  • Medication reaction: Medications can cause allergies and sensitivity reactions, which may manifest as a rash. This is not generally common in the genital area, but a medication-induced rash is not uncommon around the lips and mouth. 
  • Cancer/pre-cancer: Lesions in and around the genital area can be signs of cancer. The appearance of cancerous or pre-cancerous lesions should not have the blisters that often are present with HSV induced lesions. But if your doctor needs to distinguish between cancer and herpes, a swab or a needle biopsy (sample of the lesion) can differentiate the two concerns.
  • Concurrent HSV-1 and HSV-2: If you have HSV-1 or HSV-2, you can also become infected with the other. These are different viruses and having one of them does not cause or prevent the other. It is important to keep that in mind and to see your doctor if you develop sores in a new location because they could be herpes or a different condition. 

Frequently Asked Questions

Can a blood test detect herpes? 

Yes. There are two types of blood tests for herpes: One tests for general herpes and the other is type-specific. The general test can detect herpes antibodies, but not differentiate between types. Type-specific tests can detect antibodies for either HSV-1 or HSV-2. 

Can a urine test detect herpes? 

No. Urine tests are not used to detect herpes. Urine STD screenings test for chlamydia and gonorrhea.

Do doctors usually test for genital herpes? 

Most doctors do not routinely test for herpes unless you specifically ask or have symptoms including genital pain, redness, swelling, sores, or blisters. If you have been exposed to genital herpes or would like to be tested for peace of mind, talk to your doctor about testing options. 

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