Contamination of cerebrospinal fluid specimens with hematogenous blasts in patients with leukemia

Hematogenous blasts in cytologic preparations of cerebrospinal fluid (CSF) have generally been thought to indicate leukemic involvement of the central nervous system (CNS). However, two leukemic patients who came to autopsy had no CNS involvement despite positive CSF preparations shortly before death. Both patients had over 10,000 blasts/cu mm in their peripheral blood. The CSF specimen from one patient was grossly bloody, but the specimen from the second patient was clear. An experiment was designed to test the hypothesis that membrane filter techniques are sufficiently sensitive to detect blasts in CSF contaminated by amounts of leukemic blood too small to be detected visually. Blood from a leukemic patient with 130,000 cells/cu mm was serially diluted in CSF from 1:20 to 1:1,600,000 and membrane filters from each dilution were examined. No blood could be detected visually at the 1:8,000 and further dilutions. Blasts forms were seen on membrane filter preparations down to the 1:1,600,000 dilution, which contained 0.000000125 ml of blood, equivalent to about 1/40,000th the volume of an 18-gauge spinal needle. These findings suggest that contamination of CSF specimens with minute amounts of blood, undetectable by visual inspection, may lead to erroneous interpretation of leukemic involvement of the CNS.