Objective To analyze the expression and diagnostic value of procalcitonin(PCT),white blood cell count(WBC),and C-reactive protein(CRP)in respiratory infections in the intensive care unit(ICU),and their correlation with the clinical pulmonary infection score(CPIS).Methods A total of 105 patients with respiratory infections admitted to the ICU from March 2019 to June 2024 were selected as the observation group,while 117 patients with no respiratory infection in the ICU were selected as the control group.PCT levels in both groups were measured using the Zybio-Q7 immunoquantitative analyzer,WBC levels were measured using XT-4000i white blood cell analyzer,and CRP levels were measured using the immunoturbidimetric method.The relationship between the expression of PCT,WBC and CRP and the clinical characteristics and CPIs score of respiratory infection in ICU were analyzed.Results The proportion of patients in the observation group with ICU stay>15 days and mechanical ventilation>7 days was significantly higher than that in the control group(P<0.05).Compared to the control group,the levels of PCT,WBC,CRP and CPIS score in the observation group were elevated,with statistically significant differences(P<0.05).Multivariate logistic regression analysis showed that ICU stay>15 days(OR=4.087),PCT(OR=6.543),WBC(OR=2.652),and CRP(OR=8.964)were risk factors for the occurrence of respiratory infections in the ICU.Pearson correlation analysis indicated a positive correlation between PCT and CPIS scores(r=0.925,P=0.001),a positive correlation between WBC and CPIS scores(r=0.739,P=0.001);and a positive correlation between CRP and CPIS scores(r=0.948,P=0.001).The ROC curve demonstrated that the combined diagnostic value of the three markers for ICU respiratory infections was higher than that of PCT,WBC,or CRP alone(P=0.002).Conclusion The combination of PCT,WBC,and CRP has high diagnostic value for ICU respiratory infections and is positively correlated with CPIs scores.Therefore,the above indicators can provide a reliable basis for the early diagnosis of respiratory infection in ICU.