Normal CSF has very few cells present and appears clear. Normally there are no red blood cells present in CSF, so presence of RBCs may be due to traumatic tap or may indicate leaking of blood into CSF during sample collection. Increased white blood cells suggest an infection, leukemic infiltration or inflammation of central nervous system. Different types of WBCs will be increased in different infections such as elevated neutrophils in bacterial infections, increased lymphocytes in a viral or fungal infection or multiple sclerosis. Increased eosinophils indicate parasitic infection. CSF cytology is usually done in suspected metastatic cancer or CNS tumor in order to help diagnose the type of cancer.