129 The Risk of Blood Culture Contamination Associated With Specimen Collection Through Peripheral Intravenous Catheters

Abstract

Blood culture contamination is a common, costly, and preventable problem resulting in lower health care quality. Cultures are frequently obtained through peripheral intravenous catheters in the emergency department (ED) because of the perception that this technique avoids additional venipuncture, which can be painful for patients, time-consuming for health care workers, and increases the risk for needle stick injuries. It is unknown whether culture collection through peripheral intravenous catheters increases the risk of contamination compared to collection by fresh peripheral venipuncture. The purpose of this study was to quantify the risk of contamination associated with obtaining blood cultures through peripheral intravenous catheters compared to collection by fresh peripheral venipuncture. We conducted a matched cross sectional study of blood cultures collected from adult patients for clinical purposes between January 1 and December 31, 2009 in the ED and in-patient units at a tertiary care, university-affiliated hospital. We matched cultures collected through a peripheral intravenous catheter to cultures obtained by fresh peripheral venipuncture from the same patient within a 4-hour period. Positive cultures were categorized as truly positive or contaminated based on a standardized algorithm involving review by 3, independent, blinded infectious disease specialists. For the primary analysis, the relative risk (RR) with 95% confidence intervals (CI) of contamination among peripheral intravenous catheters -cultures was calculated with fresh peripheral venipuncture -cultures as a referent. In a secondary analysis, the proportion of truly positive peripheral intravenous catheters -cultures was compared to fresh peripheral venipuncture -cultures. During the study period, 27,806 blood cultures were collected; 4,539 cultures were obtained through peripheral intravenous catheters and 1,555 of these peripheral intravenous catheter-drawn cultures were matched to fresh peripheral venipuncture -cultures. The risk of contamination associated with collection through peripheral intravenous catheters was 6.11%, compared to 3.15% for cultures collected by fresh peripheral venipuncture (RR 1.94, 95% CI 1.40 - 2.68). Cultures collected through peripheral intravenous catheters had an 8.68% true positive rate, compared to 7.52% for cultures collected by fresh peripheral venipuncture (RR 1.15, 95% CI 1.02 - 1.29). Obtaining 1,000 cultures through peripheral intravenous catheters instead of by fresh peripheral venipuncture would result in 30 additional contaminated cultures and 12 additional true positives. While blood cultures collected through peripheral intravenous catheters are more convenient and safer for health care workers, less painful for patients, and may yield more true positive results compared to cultures collected by fresh peripheral venipuncture, they are also associated with a substantially higher risk of contamination. Policymakers developing protocols for blood culturing practices must weigh this elevated risk of contamination against the advantages of catheter-drawn specimens.