When doctors suspect meningitis, they must quickly determine whether it is from a bacterial, viral, fungal, or other type of infection or from irritation caused by something other than an infection (for example, a chemical). The possible causes are many, and the treatment differs for each. The test usually used to diagnose meningitis and determine its cause is the spinal tap, or lumbar puncture. A thin needle is inserted between two bones in the lower spinal column to withdraw a sample of cerebrospinal fluid from an area just below the spinal cord. The doctor then examines the fluid for bacteria under a microscope and sends a sample of it to the laboratory to be cultured and identified. The bacteria can be tested for susceptibility to treatment with different antibiotics. The sugar level, an increase in protein, and the number and type of white blood cells in the fluid also help determine the type of infection.