Cold Sores (cont.)
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Cold Sores Diagnosis
The diagnosis of cold sores is usually based on the appearance of the lesions. Usually, no laboratory test is needed because most sores that look like cold sores are cold sores. Occasionally, mouth sores known as canker sores may be mistaken for cold sores. However, canker sores occur inside the mouth whereas recurrent cold sores usually occur on the lips. If there is a question about the diagnosis, a variety of tests are available, including viral culture and polymerase chain reaction (PCR). To do these tests, a swab is rubbed over an active blister. Swabbing the blister in an attempt to culture the virus in the lab works best in the first 24-48 hours before the blister has crusted over. There is also a way to test for herpes DNA in a swab that has been rubbed on the sore. This type of testing is called a "polymerase chain reaction" or PCR for short. PCR testing is very good at detecting herpes virus, but it is not as readily available as culture.
Blood tests for antibodies are not very useful, because finding antibodies to herpes just means that the body has been exposed to this virus at some point in the past. It does not tell if the current sore is due to herpes.
If the diagnosis is in doubt, the best approach is to encourage the person to see a doctor at the first sign of a sore. That will allow the clinician to see active lesions that can be tested by culture or PCR. If a delay is anticipated in being seen, a mobile phone or camera can be used to take pictures of the lesion to show to the physician.
Medically Reviewed by a Doctor on 8/13/2015
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