Background: Central line associated bloodstream infection (CLABSI) is considered one of commonest complications that are associated with increased cost of care, extended hospital stay and increased mortality. An early and accurate diagnosis is critical for improving the prognosis in patients with CLABSI. Presepsin is a biological biomarker which has a good value in early detection of different infections. Objective: to investigate the value of serum presepsin in diagnosis of CLABSI in adult patients admitted to intensive care units (ICUs). Methodology: The study was conducted on 56 clinically suspected CLABSI cases, admitted to ICUs of Ain Shams University hospitals and 30 healthy individuals of matched age and sex as control group. Blood samples were collected from patients for conventional blood culture and for detection of 16S & 18S rDNA by nested multiplex PCR for culture negative samples. Quantitative measurement of serum presepsin by Human Presepsin ELISA kit was applied for both, patients with confirmed CLABSI (n=30) and healthy controls (n=30). Results: CLABSI diagnosis was confirmed in 30 patients, with most common isolated organisms were Klebsiella pneumoniae and Enterococcus spp. (6/31, 19.4% for each). The mean value of serum presepsin among confirmed CLABSI cases was higher than healthy controls and the difference was statistically highly significant (819.33ng/L versus 161.33 ng/L). Serum presepsin could be used to discriminate cases from controls at a cutoff level of ≥ 455 ng/L. Conclusions: Serum presepsin is a promising biomarker that aids in early diagnosis of CLABSI, thus offering early antimicrobial treatment which leads to improving patients' mortalities. Further studies on large scales are recommended to assess the prognostic value of serum presepsin in such critically ill patients and to monitor patients' response to therapeutic actions.