The CD-57 is a type of a natural killer white blood cell that often is less than normal in chronic Lyme disease. Some other Lyme literate medical doctors recommend it as a way to see if a person has Lyme and to follow the course of his/her treatment. I rarely recommend a CD-57 test because in most situations it is not useful and has no real predictive or helpful value in charting the course of a person's care. See why in this Lyme Byte from our webinar Conversations with Marty Ross MD on 09/10/13.