Objective: To evaluate the impact of a preliminary positive blood culture result, subsequently confirmed to be a false positive blood culture result on rate of hospitalization, antibiotic therapy and use of microbiologic tests.
Design: Retrospective chart review.
Patients and methods: Children between 1 month and 18 years old on whom a blood culture was performed were eligible, excluding those with an underlying condition for whom a false positive blood culture may be difficult to assess. During the 1-year study period 9959 blood cultures were performed of which 778 (7.8%) produced growth. Charts of 81 patients with a false positive blood culture were reviewed and compared with those of 162 patients with a true negative blood culture. Patients already hospitalized when blood culture was drawn (n = 24) were analyzed separately from those who were not (n = 219). Among these, patients were divided into those who were followed as outpatients (n = 104) and hospitalized (n = 115).
Results: Both groups (false positive vs. true negative) were comparable for age, sex, temperature at consultation, white blood cell count and illness severity. Twenty-six percent of patients followed as outpatients who had a false positive blood culture were hospitalized because of a preliminary positive blood culture result. Among patients hospitalized at the initial assessment, the frequency of antibiotic therapy (91% vs. 71%, P < 0.01), the frequency of use of intravenous antibiotics (80% vs. 58%, P < 0.01) and the percentage of unwarranted antibiotic prescription (13% vs. 0%, P < 0.01) were significantly greater in the false positive group than in the true negative group. The same results were found for each of these outcomes among the group of patients followed as outpatients (61% vs. 28%, P < 0.01, 17% vs. 0%, P < 0.01 and 39% vs. 0%, P < 0.01) for false positive vs. true negative, respectively. Patients with false positive blood cultures had more blood cultures drawn subsequently (P < 0.01). Children already hospitalized when the blood culture was obtained did not show significant differences in main outcomes.
Conclusions: False positive blood culture results generate unnecessary hospitalizations, antibiotic therapy and use of microbiologic tests.