Risk of blood culture contamination during central venous catheter insertion in critically ill adults: a...

Blood cultures are often obtained during central venous catheter (CVC) insertion in intensive care units (ICUs), but contamination risk has not been fully evaluated while accounting for patient-level and short-term clinical factors.

We conducted a single-centre retrospective study of all blood culture sets obtained in an eight-bed adult ICU between June 2023 and June 2025. We compared contamination rates between cultures obtained from the CVC hub during insertion and those obtained from other sites. A self-controlled, same-day within-patient paired analysis was performed to reduce confounding.

Among 1,196 blood culture sets from 316 patients and 331 ICU admissions, the primary analysis included 102 same-day matched pairs from 88 ICU admissions involving 86 patients. In this self-controlled, same-day within-patient analysis, CVC-insertion hub cultures were associated with higher odds of contamination than comparator cultures (OR 2.58, 95% CI 1.21-5.51). The finding was consistent after restriction to arterial-line comparator cultures and in analyses using 7- and 14-day within-patient matching windows.

Blood cultures obtained from the CVC hub during insertion were associated with an increased risk of contamination. These cultures should be interpreted with caution, and alternative sampling sites may be preferable when feasible.