The JCBK test (JC virus gene assay) is a laboratory test aimed at detecting the presence of the JC virus, which is part of a common family of viruses. This virus can remain dormant in the body for long periods but may become active in certain situations, especially in individuals with weakened immune systems. The test is used to diagnose neurological disorders, such as JC virus–related encephalitis, which can lead to serious symptoms like confusion, memory loss, and movement difficulties. The test is usually performed by analyzing a blood sample or cerebrospinal fluid. The results help doctors determine the presence of the virus, allowing them to develop an appropriate treatment plan and improve patient care.