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Diagnosing Fever Blisters

Before diagnosing fever blisters, healthcare providers will consider other conditions that share similar symptoms, such as chickenpox or syphilis. He or she will also ask about current symptoms you are experiencing, any recent illnesses or injuries, and any drugs you are taking. A fever blister diagnosis is usually made at this time, but blood tests or viral cultures may be needed to confirm the diagnosis.

How Is a Fever Blister Diagnosed?

When diagnosing a fever blister (also known as a cold sore or known medically as herpes labialis), a healthcare provider will begin by asking a number of questions. This will include questions about:
  • Current symptoms you are experiencing
  • Other medical conditions that you may have
  • Any recent illnesses or injuries
  • Any medicines you are taking.
The healthcare provider will also perform a physical exam to look for signs and symptoms (see Symptoms of Fever Blisters).
A fever blister diagnosis can often be made based on the answers to the questions, as well as by looking at the sores. However, in some cases, fever blisters may be more difficult to diagnose. In these cases, other tests may be recommended.

Tests for Diagnosing Fever Blisters

To help confirm a diagnosis of fever blisters, a viral culture of the sore or a blood test can be used to detect the herpes virus. With a viral culture, a healthcare provider uses a swab to obtain and study material from a suspected herpes sore. This test will confirm the presence and type of herpes simplex virus (HSV). It may take 2 to 10 days for the results to return from the lab.
You may still have a herpes infection, however, even if your culture is negative (which means it does not show HSV). For example, if the lesion has started to heal, the swab may not pick up enough virus, and the culture result will be a "false negative." In these cases, a blood test may be recommended.
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Fever Blister Information

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