Infection biomarkers in assisting the judgement of blood stream infection and patient prognosis: a retrospective study incorporating principal components analysis.

Background: This study aimed to evaluate whether inexpensive and quickly available infection biomarkers including procalcitonin (PCT), C-reactive protein (CRP), white blood cell (WBC) count, and percentage of neutrophils (N%) are helpful in assisting the judgement of blood culture results and patient prognosis.

Methods: This retrospective study included patients who were admitted to the intensive care unit (ICU) of Changzheng Hospital from July 2015 to June 2017 and had at least one episode of blood culture with matched infection biomarkers (PCT, CRP, WBC, and N%). Primary infection biomarkers were transformed into newly derived components using the principal component analysis (PCA) method. Each observation was plotted as a point on the component map using factor scores as coordinates. The distribution characteristics of patients with different blood culture results and prognosis were explored. The diagnostic performance of the components and infection biomarkers in the discrimination of blood culture results and patient prognosis were compared using receiver operating characteristic (ROC) curves.

Results: A total of 768 episodes of blood cultures from 436 patients were analyzed. Patients with positive blood cultures were associated with higher ICU mortality, in-hospital mortality, longer ICU stay and hospital stay (P<0.001 for all). In PCA, the 4 sets of primary infection biomarkers (PCT, CRP, WBC, and N%) were transformed into components 1 and 2. On the component map, observations of positive blood cultures were more likely to be distributed in the first and second quadrants than those of negative blood cultures (OR, 6.28, 95% CI, 4.14-9.64, P<0.001). Compared to patients with negative blood cultures, non-survivors with positive blood cultures were more likely to be distributed in the first and second quadrants (OR, 6.90, 95% CI, 2.67-20.98, P<0.001), followed by survivors with positive blood cultures (OR, 3.44, 95% CI, 1.97-6.13, P<0.001). PCT- and CRP-derived component had the largest area under curves (AUCs) in the discrimination of blood culture results (0.81) and patient prognosis (0.69).

Conclusions: PCT- and CRP-derived component was more strongly associated with blood culture results and patient prognosis than WBC- and N%-derived component and primary biomarkers.