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Cold sores have very recognizable features. They are most often diagnosed by physical exam and by your medical history. If your doctor is not sure, a sample of the fluid or tissue from the blister may be taken. A blood sample may also be taken for testing.

Testing may include any of the following:

  • Viral culture—A sample of the fluid from the cold sore blisters is taken with a cotton swab. This is done as soon as possible after an outbreak begins. The virus is then grown in the laboratory. This test is very accurate if the sample is taken while there are still clear blisters.
  • Tzanck test—The cold sore is lightly scraped to collect cells onto a glass slide. These cells are then examined under a microscope. This test is quick, but not as accurate.
  • Tests to detect the presence of antibodies in your blood. These particular antibodies are created by your body to fight herpes simplex virus (HSV) infections. This test may be done when no sores are present.

References:

Cold sores. Nemours Kids Health website. Available at: http://kidshealth.org/parent/infections/common/cold_sores.html. Updated October 2010. Accessed March 30, 2013.

Herpes labialis. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated May 27, 2011. Accessed March 20, 2013.

Herpes simplex: Diagnosis, treatment, and outcome. American Academy of Dermatology website. Available at: http://www.aad.org/skin-conditions/dermatology-a-to-z/herpes-simplex/diagnosis-treatment/herpes-simplex-diagnosis-treatment-and-outcome. Accessed March 20, 2012.



Last reviewed March 2014 by David L. Horn, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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