The Collection of Additional Blood Samples Improves Bacteremia Detection

Researcher taking blood sample from a rack of medical samples.
Researchers assessed whether the collection of additional blood samples increases the probability of bacteremia detection among hospitalized patients.

Obtaining additional blood culture samples increased the probability of bacteremia detection among hospitalized patients, according to results of a study published in JAMA Network Open

The clinical utility of collecting additional blood culture from hospitalized patients is not clear. To address this knowledge gap, researchers retrospectively analyzed blood samples obtained from patients at a tertiary hospital between January 2019 and January 2020. The analysis included adult patients for whom 2 or more blood samples were collected for culture analysis, with the first sample collected in the emergency department within 24 hours of hospital admission. Patients who had received a hematopoietic stem cell transplant were excluded. The period of incubation for samples in which bacteremia was detected was considered the microbiologic time to positivity (mTTP). The primary outcome was the likelihood of bacteremia detection from blood samples collected 24 hours after the first sample. 

A total of 23,088 blood samples were included in the analysis, representing 2863 patients. Of these samples, bacteremia was detected in 8.34% (95% CI, 7.90-8.70), with 0.29% (95% CI, 0.28-0.30) of positive results due to contamination. Among 78.6% (95% CI, 74.8-78.6) of blood samples in which bacteremia was detected, the mTPP was 24 hours or less, and most samples were positive for gram-negative bacilli and anaerobic microorganisms. 

There were 446 blood samples for which the mTTP was greater than 24 hours. Of these samples, 317 (71.1%) were the first collected sample, 14.5% (95% CI, 11.4-17.9) were contaminated, and 129 (28.9%) were collected following hospital admission. The probability of bacteremia detection via culture analysis of the second sample was 4.1% (95% CI, 3.9-4.4). However, the probability of bacteremia detection decreased to 2.6% (95% CI, 2.4-2.8) after samples obtained from patients with endovascular infections were excluded. 

Factors associated with a decrease in the odds of positive bacteremia detection included female sex (odds ratio [OR], 0.34; 95% CI, 0.18-0.63; P <.001); hourly mTTP increment (OR, 0.98; 95% CI, 0.97-0.99; P =.005); sampling from a catheter (OR, 0.22; 95% CI, 0.10-0.47; P <.001); and collection of a sample for which cultures grew gram-positive microorganisms (OR, 0.04; 95% CI, 0.02-0.13; P <.001).

The study was limited by its retrospective design and potential misclassification bias due to the use of data from electronic health records. 

According to the researchers, “these findings support development of novel guidelines for [blood culture] sample collection to improve diagnostic resource use and patient management and to reduce costs and support rapid transportation and incubation of [blood cultures] to improve bacteremia diagnosis.”

Reference

Zanella MC, de Lorenzi-Tognon M, Fischer A, Vernaz N, Schrenzel J. Bacteremia detection in second or subsequent blood cultures among hospitalized patients in a tertiary care hospital. JAMA Netw Open. 2022;5(4):e228065. doi: 10.1001/jamanetworkopen.2022.8065