csf tap test csf tap test 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 30-50 ml of cerebrospinal fluid (csf) through a lumbar puncture, after which motor and cognitive function is clinically reassessed. the name "fisher test" is after c. miller fisher, a canadian neurologist working in boston, massachusetts, who described the test. csf tap testlumbar puncturesynonymslumbar tap testpurposetest to decide shunting of cerebrospinal fluid clinical improvement showed a high predictive value for subsequent success with shunting. a "negative" test has a very low predictive accuracy, as many patients may improve after a shunt in spite of lack of improvement after csf removal.