CSD skin test
The cat scratch disease (CSD) antigen, which consists of sterile pus derived from a human lymph node from someone known to have CSD, is injected under the skin to help determine if you have been infected with the disease.
How the test is performed
The antigen is injected just under the skin, usually on the forearm, so that a small lump pushes the skin up. The lump indicates that the antigen has been injected at the correct depth. The site is labeled, usually with a pen.
After 48 to 72 hours, a medical provider will check the site of the injection to determine whether there has been a reaction.
How to prepare for the test
There is no special preparation. People with dermatitis or other skin irritations should have the test performed at a location where no irritation is present.
How the test will feel
When the antigen is injected, you may feel a stinging sensation where the needle is inserted. After the reaction begins, the area may itch or burn.
Why the test is performed
This test was used more extensively in the past, before Bartonella henselae, the bacteria that causes CSD, was identified.
There should be less than a 5 mm inflammation zone of the disease antigen.
What abnormal results mean
An inflammation zone of greater than 5 mm may indicate that you have been infected with cat scratch disease recently or in the past.
What the risks are
Because the antigen is obtained from sterile pus derived from human lymph nodes, there is a small potential risk of transmission of viruses. Also, there are occasional local reactions that may occur such as itching and rarely hives.
Although this test has historical value since it was used in the past as one of the criteria for diagnosis, there are better tests available for the diagnosis of CSD. In addition, the CSD antigen has not been standardized, is not widely available, and carries the potential risk of transmitting other pathogens such as viruses.
by Harutyun Medina, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.