To determine the clinical significance of surfactant protein D (SP-D), a useful marker for evaluating interstitial lung diseases and specifically in rheumatoid arthritis associated interstitial lung disease patients.
Our patients were classified into 3 groups (Group 1: 18 patients had rheumatoid arthritis ILD; Group 2: 12 patients had rheumatoid arthritis without interstitial pulmonary disease; Group 3: 10 patients had idiopathic pulmonary fibrosis with no rheumatoid arthritis) and 20 healthy control subjects. Serum SP-D levels were assayed using a specific enzyme-linked immunosorbent assay for all studied groups.
A highly significant difference was found between patients’ groups and the control group regarding disease duration, serum aCCP, SP-D, serum CRP and RF being higher in patients’ group (p < 0.01). However FVC was significantly lower in patients’ groups compared to the control group (p < 0.05). Assessment of the diagnostic performance of SP-D assay revealed that the best cutoff for discriminating rheumatoid patients with interstitial lung disease from those without interstitial lung disease was 219 ng/mL. At this value, SP-D had a diagnostic sensitivity of 94.2%, specificity 90%, negative predictive value 90%, positive predictive value 94.2% and efficiency 95%.
The serum SP-D level may be a useful marker for ILD especially in patients with rheumatoid arthritis.