[Serum markers in patients with idiopathic pulmonary alveolar proteinosis]

Pulmonary alveolar proteinosis (PAP) is a rare lung disease characterized by PAS positive lipoproteinaceous material accumulation in the pulmonary alveoli, of which autoimmune (APAP) or idiopathic type (IPAP) accounts for about 90%. Several serum markers were reported to be valuable in IPAP diagnosis. However, data in Chinese patients was not available. Here we analyzed the diagnostic value of serum markers in Chinese IPAP patients.

Thirty-one IPAP patients, 25 healthy volunteers and 15 patients with other lung diseases were enrolled in the study. Anti-GM-CSF antibody, SP-A, SP-D and YKL-40 levels of the serum samples were tested by ELISA method. LDH, CEA, arterial blood gas analysis and pulmonary function test results were collected and analyzed. Then the difference between the groups and the relationship between the 2 of the markers were tested.

The level of serum anti-GM-CSF antibody, SP-A and SP-D [29.80(13.02-53.86) mg/L, (47 ± 30) and (77 ± 57) µg/L respectively] were higher in IPAP patients than in healthy volunteers and disease control patients (P < 0.05). IPAP and disease control groups had higher YKL-40 and LDH levels than the healthy control group (P < 0.05), but no statistical difference between the former 2 groups (P > 0.05). The CEA level of IPAP patients was higher than that of the disease control group (P < 0.05). The sensitivity and specificity of anti-GM-CSF antibody in IPAP diagnosis were both 100% at the cut-off value of 2.46 µg/mL. The LDH, CEA and SP-A levels correlated positively with P(A-a) O₂ and negatively with TL(CO)%, PaO₂ and SaO₂ (P < 0.05). The SP-D level correlated negatively with SaO₂ (P < 0.05), and positively with LDH and CEA level (P < 0.05), so did SP-A (P < 0.05). YKL-40 correlated positively with SP-A but not with other markers. Anti-GM-CSF antibody did not correlate with any of the markers.

Serum anti-GM-CSF antibody testing showed high sensitivity and specificity for the diagnosis of APAP, though it did not correlate with disease severity. Serum LDH, CEA, SP-A and SP-D levels were elevated in IPAP patients and correlated well with disease severity. YKL-40 level was also higher in IPAP patients, but it could not be used as a disease severity marker.