Herpes simplex virus (HSV) is a widespread viral infection that can cause sores or blisters on various parts of the body, most commonly around the mouth (oral herpes) or genitals (genital herpes). While physical examination can often suggest a diagnosis, laboratory tests are frequently used to confirm the presence of the virus and guide appropriate management. One such diagnostic method is the herpes culture test, which aims to identify the live virus from a lesion.
Understanding the Herpes Culture Test
A herpes culture test is a laboratory procedure designed to detect an active herpes simplex virus infection. It works by attempting to grow live, replicating virus particles from a collected sample in a controlled environment. If the virus is present and viable, it will multiply within the cell culture, allowing laboratory technicians to identify it. This direct detection method confirms if visible lesions are caused by the herpes virus and indicates current viral shedding.
How a Herpes Culture is Performed
Performing a herpes culture involves collecting a sample directly from an active lesion, such as a blister or sore. A healthcare provider gently rubs a sterile cotton swab over the lesion to collect fluid and cells. For blisters, opening them may be necessary to obtain a sufficient sample.
The effectiveness of this collection hinges on the lesion being fresh, ideally within 48 hours of symptoms appearing, as older or healing sores may contain less active virus. Once collected, the swab is transported to a laboratory where the sample is placed into a special cell culture dish. The culture is then monitored for signs of viral growth over several days. Results can become available within 16 hours to 7 days, depending on the specific laboratory methods used.
Deciphering Herpes Culture Results
Interpreting the results of a herpes culture test involves understanding what the presence or absence of viral growth signifies. A “positive” result indicates that the herpes simplex virus was successfully grown and identified from the collected sample. This outcome confirms an active HSV infection at the site from which the sample was taken.
Conversely, a “negative” result means that no herpes virus was detected or grown in the laboratory culture. While a negative result might suggest the absence of an active infection, it does not always definitively rule out herpes. A negative culture result does not necessarily mean an individual has never been infected with herpes.
When a Culture Test Isn’t Enough
The herpes culture test has limitations, especially regarding its sensitivity. Its sensitivity is lower compared to other diagnostic methods, especially when lesions are not new or contain a low concentration of the virus. This can lead to false negative results, where an individual has herpes but the test does not detect it. For instance, sensitivity can be as low as 25-70% for recurrent outbreaks or if the sample is taken beyond 48 hours of symptom onset.
Due to these limitations, other diagnostic options are frequently employed, offering greater sensitivity. Polymerase Chain Reaction (PCR) tests, for example, detect the genetic material (DNA) of the herpes simplex virus. PCR tests are more sensitive and accurate for diagnosing active lesions, especially when lesions are older or have begun to heal, and results can be available within 24 hours.
Blood tests, specifically antibody tests, represent another diagnostic approach. These tests do not detect the virus itself but rather look for antibodies that the immune system produces in response to an HSV infection. Immunoglobulin G (IgG) antibody tests indicate past exposure to the virus and are useful for screening or determining exposure history, even in individuals without active symptoms. However, antibody tests cannot determine the exact location of the infection or whether a current outbreak is occurring, and they may produce false negatives if taken too soon after exposure, as antibodies can take weeks to months to develop.