Evaluating Elevated CRP Levels as an Infection Marker: Implications for Chemotherapy Cycles in Lung Cancer Patients

Infection is a prevalent cause of mortality and morbidity in patients with lung cancer. Moreover, infection diagnosis is challenging in such patients. C-reactive protein (CRP) is a frequently used marker in the clinical diagnosis of infection. Notwithstanding the foregoing, CRP may already be elevated in cases of malignant neoplasms, and in addition to malignancy, causal factors such as noninfectious infarction, inflammation, injury, drug reactions, and thrombosis may also be frequently associated with elevated CRP in such patients. The present study investigated the situations wherein higher CRP levels could be considered as the manifestation of infection that might hinder chemotherapy procedures and aimed to determine a cutoff value that could predict infection.

This study prospectively included patients with lung cancer and high CRP values. The clinical features of the patients, along with laboratory and radiographic results, were assessed. Considering the final decision of the physician who followed up with the patients, they were divided into two groups: infected and noninfected groups. Intergroup comparisons were performed for clinical, laboratory, and radiological results. The receiver operating characteristic curve analysis was used to review the diagnostic value of serum CRP levels in predicting infection in patients with lung cancer. The CRP cutoff value to be considered for predicting infection was calculated.

At the time of admission, the mean CRP level of the 180 patients included in the study was 4.5 mg/dL. As per the physician's decision, 23 patients (12.8%) were found to have an infection. For the 23 infected patients, the mean CRP value at admission was 13.0 mg/dL, whereas it was 3.36 mg/dL for the 157 patients who were considered to be noninfected. The mean CRP value of the infected patients was significantly higher compared to that of the noninfected patients (p<0.001). For the 23 infected patients who were then treated with antibiotics, the mean CRP levels at admission and after treatment were 12.79 mg/dL and 5.4 mg/dL, respectively. There was a significant difference of 7.35 units between the two levels mentioned above (p<0.001). The CRP cutoff value at admission to be considered for predicting infection that would hinder chemotherapy in all patients was ≥6.74 mg/dL with a sensitivity, specificity, positive predictive value, and negative predictive value of 91.3%, 86.6%, 50%, and 98.6%, respectively (p<0.001).

This study suggested cutoff values to distinguish infection-associated high CRP levels from other causal factors that might induce an increase in CRP levels in patients admitted for chemotherapy administration. The suggested cutoff values can prevent unnecessary delays in chemotherapy cycles by eliminating false considerations of infection in patients with high CRP levels.