Diagnosing Cold Sores
When diagnosing cold sores, healthcare providers usually ask about a person's current symptoms, existing medical conditions, and any recent illnesses or injuries. Some cold sores are more difficult to diagnose and may require tests such as viral cultures or blood tests. Before making a cold sore diagnosis, healthcare providers will also consider other conditions that share similar signs or symptoms, such as chickenpox.
When diagnosing a cold sore (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 of cold sores (see Cold Sore Symptoms).
A cold sore diagnosis can often be made based on the answers to the questions, as well as by looking at the sores. However, in some cases, cold sores may be more difficult to diagnose. In these cases, other tests may be recommended.
To help confirm a diagnosis of cold sores, 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 sore 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.