Background: Procalcitonin (PCT) and C‑reactive protein (CRP) are two common and practical biomarkers for various diseases. However, their roles in scrub typhus (ST) have not been extensively investigated.
Aim: In this study, we compared the effectiveness of PCT and CRP levels and the PCT/CRP ratio and evaluated their predictive performance in the diagnosis of ST.
Methods: Patients with acute febrile illness and suspected ST infection treated at our hospital between January 2015 and December 2016 were retrospectively evaluated. An indirect immunofluorescent assay was used to confirm the presence of ST. Documented information included initial clinical images and laboratory data including PCT or CRP. Receiver operating characteristic curve analysis with area under curve (AUC) identified the optimal PCT, CRP, and PCT/CRP ratio cutoff values for the diagnosis of ST.
Results: Among 189 patients with acute febrile illness, 153 (89.9%) tested positive for ST. CRP and PCT level data were available in 168 (88.8%) and 42 (22.2%) patients, respectively. Thirty patients (15.9%) underwent both CRP and PCT tests. ST‑positive samples contained significantly higher levels of PCT (P < 0.001) and CRP (P = 0.015) than those of the 36 non‑ST samples. No difference was observed in the PCT/CRP ratio (P = 0.477). The optimal cutoff values were 0.27 ng/mL, 1.65 mg/dL and 0.036 for PCT and CRP levels and PCT/CRP ratio, respectively. PCT level showed the best diagnostic performance (sensitivity = 89.3%; specificity = 92.3%; AUC = 0.894; 95% confidence interval [CI] =0.753–0.925). Combining PCT and CRP levels based on the respective optimal cutoff points further improved the performance of ST diagnosis (AUC = 0.906, 95% CI = 0.894–0.923), with 89.5% sensitivity and 91.7% specificity. PCT level was positively correlated with liver enzyme levels, and acute hepatitis could be identified with high specificity (100%) using a cutoff PCT threshold of 0.36 ng/mL.
Conclusion: PCT is useful in ST diagnosis, and pending conformation in future studies may reflect hepatic dysfunction at initial presentation.