Samples should not be collected from the external ventricular drainage cerebrospinal fluid collection bag due to the rapid degradation of cellular components. Though samples can be drawn from the distal port, white cell counts and cultures are often not accurate 1).

1)
Wong FW. Cerebrospinal fluid collection: a comparison of different collection sites on the external ventricular drain. Dynamics. 2011 Fall;22(3):19-24. PMID: 21941814.