Introduction: Diagnostic alternatives that allow microbial identification in blood, such as molecular biology; have shown utility in neonatal sepsis. Objective: To evaluate the impact of a Light Cycler SeptiFast test (LCSF) on days of hospital stay and the use of newborn (NB) antibiotics with suspected sepsis. Methods: We included NB with LCSF test and blood culture (cases) and NB with only blood culture (controls). We evaluated the days of stay, days of antimicrobial use and number of deaths. Statistic analysis: Descriptive statistics was used. The association between the use of LCSF and variables such as mortality, days of stay, use of antimicrobials, and use of mechanical ventilation was analyzed by odds ratio with 95% CI. Results: We included 20 subjects in the case group and 40 in the control group. 8 (40%) of the cases were positive vs 6 (15%) of the controls in the control group. In the controls, the average days of stay were 65 + 15 vs 35 + 10 days of the cases (p < 0.05). There was no significant difference in mortality, nor in antimicrobial use. The use of molecular biology was a protective factor for prolonged stay OR 0.2 (95% CI 0.08 -0.5) p = 0.001. Conclusions: The LCSF test influences the days of hospital stay, but does not impact mortality or the use of antimicrobials.