[Value of studying the extraluminal and intraluminal surfaces in the detection of catheter colonization].

612 catheters have been prospectively investigated. In all of them, both the external and the internal surfaces were cultured, the former with the semiquantitative technique of Maki and the latter with the semiquantitative technique of Liñares. 102 of the 469 central venous catheters (22%), 21 of 70 catheters used for parenteral nutrition (30%), and 19 of the 73 arterial catheters (26%) were positive with one or both techniques. The external surface was positive in 95% of central venous catheters, in 90% of the parenteral nutrition catheters, and in 95% of the arterial catheters, whereas the internal surface was positive in only 59%, 62% and 42%, respectively. The routine study of the internal surface of the catheters does not appear as justified. In our opinion, the microbiological study of catheters should be individualized depending on the relative importance of the skin or the connections in a particular catheter type. The quantitative study of the intraluminal surface should only be carried out in those catheters where connections represent a significant pathogenetical route. These catheters constitute only a small proportion of those that we receive for culture in the Microbiology Laboratory; therefore, this approach represents a considerable simplification of our daily routine.