A retrospective study of the optimal number of blood cultures at a hospital in Japan

Abstract

Blood culture tests have a major role in rapid and accurate diagnosis and selection of optimal antibiotic treatment for infectious diseases. The true-positive and contamination rates of blood cultures are performance indicators for the practice of blood culture. However, the optimal number of blood cultures has not been adequately elucidated. We aimed to assess the validity of the number of blood cultures obtained in the hospital. We conducted a retrospective study of blood cultures collected from hospitalized patients between 2010 and 2014 at a tertiary care hospital in Japan and assessed the validity of the number of blood cultures per 1,000 admissions as an indicator for the optimal practice of obtaining blood culture, considering the average length of stay. We also investigated the validity of true-positive and contamination rates of blood cultures in the hospital. The number of blood cultures in this study ranged from 28.6 to 56 per 1,000 patient-days and from 404.4 to 894.6 per 1,000 admissions. The median true-positive and contamination rates of blood cultures per year was 10.1% and 2.8%, respectively. The median contamination rate of blood cultures in a community-acquired group was significantly higher than that in a hospital-acquired group (4.1% vs. 1.9%, p = 0.029). We conclude that there is a possibility that the number of blood cultures per 1,000 admissions is a more appropriate factor to evaluate than per patient-days. Moreover, the true-positive and contamination rates of blood cultures in our hospital are valid.