Determining the Prognostic Value of Complete Blood Count Subgroup Parameters in Staphylococcus aureus Bacteremia

Abstract

Purpose: Serum cytokine alterations are associated with increased Staphylococcus aureus bacteremia (SAB) mortality. Unfortunately, clinical use of these cytokines is uncommon due to limited availability and high cost. Complete blood count (CBC) with differential reflects the host immune response, and CBC subgroup parameters may have prognostic value in SAB. We sought to determine the association between CBC subgroup parameters on the day of index blood culture and 30-day all-cause mortality in SAB patients. Methods: We conducted a retrospective study of adult SAB patients with infectious diseases consultation to evaluate the discriminatory capacity of CBC subgroup parameters in predicting SAB mortality. Clinical and microbiological data were collected, including severity of illness and CBC subgroup parameters, on the day of index blood culture. The primary outcome was 30-day all-cause mortality. A multivariable logistic regression model was used to determine the association between patient-level variables and mortality. Results: A total of 119 patients were included. The overall 30-day all-cause mortality rate was 10.1%. The median neutrophil-to-lymphocyte count ratio (NLCR) among survivors was 13.6 vs 23.2 among nonsurvivors (p = .007). Median lymphocyte count among survivors was 0.9 x 103 cells/μL vs 0.6 x 103 cells/μL among non-survivors (p = .031). Median platelet count was higher among survivors than nonsurvivors (239 x 103 cells/μL vs 171 x 103 cells/μL, respectively; p = .018). All other CBC subgroup parameters were similar between the two groups. Known SAB mortality predictors, including age, were also associated with increased mortality. Lower lymphocyte count was independently associated with increased mortality (adjusted odds ratio [aOR] 0.236, 95% confidence interval [CI] 0.064-0.872), as was higher PITT bacteremia score (aOR 2.439, 95% CI 1.565-3.803). Conclusions: CBC subgroup parameters may have prognostic value in SAB. Additional study is warranted to further ascertain the prognostic value of these readily available laboratory values.

Keywords

• s. aureus bacteremia
• host response
• complete blood count
• cbc subgroup parameters
• clinical outcomes