The CSF tap test, sometimes lumbar tap test or Miller Fisher Test, is a medical test that is used to decide whether shunting of cerebrospinal fluid (CSF) would be helpful in a patient with suspected normal pressure hydrocephalus (NPH). The test involves removing 30 mL of cerebrospinal fluid (CSF) through a lumbar puncture, after which cognitive function is clinically reassessed.[citation needed] The name "Fisher test" is after C. Miller Fisher, a Canadian neurologist working in Boston, Massachusetts, who described the test.[1]