C3a is a complement protein that works with antibodies to destroy pathogens. They activate immunity through control of inflammation, destruction of pathogens by white blood cells and cell death. Elevated levels of C3a may be an early marker for acute Lyme disease. Another test, CD57, may also be used as a marker for chronic Lyme disease, but it is not always reliable. The C3a complement test should be combined with the CD57 and C4a tests.