CYFRA21-1 is a more sensitive biomarker to assess the severity of pulmonary alveolar proteinosis

Background Serum lactate dehydrogenase (LDH), carcinoembryonic antigen (CEA) and CYFRA21-1 are the commonly used biomarkers to identify patients with autoimmune pulmonary alveolar proteinosis (APAP). However, it is not clear which of the biomarkers is more sensitive to the severity of the patient’s condition. Methods APAP patients numbering 151 were enrolled in this study. All patients’ severity was assessed through the severity and prognosis score of PAP (SPSP). According to the respective laboratory upper limits of serum levels of LDH, CEA and CYFRA21-1, APAP patients were divided into higher and lower-level groups. Patients were divided into five groups based on SPSP. 88 patients had completed six months of follow-up. We calculated sensitivity, specificity, and critical point of LDH, CEA and CYFRA21-1 between APAP patients and normal control group, and between grade 1–2 and 3–5 through receiving operating characteristics (ROC) curve. Results Serum LDH, CEA and CYFRA21-1 levels of patients with PAP were higher and distinctly related to PaO2, FVC, FEV1, DLCO, HRCT scores and SPSP. The SPSP of patients in higher-level LDH, CEA and CYFRA21-1 groups were higher than those of corresponding lower-level groups. Based on SPSP results, the patients were divided into five groups (grade I, 20; grade II, 37; grade III, 40; grade IV, 38; grade V, 16). The serum level of CYFRA21-1 of patients with APAP in grade II was higher than that of patients in grade I and lower than that of patients in grade III. Serum CYFRA21-1 of patients with APAP after six months were higher than the baseline among the aggravated group. Serum LDH, CEA and CYFRA21-1 levels after six months among patients in the relieved group of patients with APAP were lower than the baseline. ROC correlating LDH, CEA and CYFRA21-1 values with APAP severity (between grade 1–2 and 3–5) showed an optimal cutoff of LDH of over 203 U/L ( 3.3 ng/ml) (AUC: 0.815, 95% CI [0.748–0.882], sensitivity: 0.606, specificity: 0.877). Conclusion Serum CYFRA21-1 level was more sensitive in revealing the severity of APAP than LDH and CEA levels among mild to moderate forms of disease.