Serum surfactant protein A as a surrogate biomarker of a negative heart sign among patients with interstitial lung disease

The mechanisms underlying interstitial lung disease (ILD) are characterized by variable inflammation or fibrosis of the pulmonary interstitium. A negative heart sign (NHS) on (67)Ga scintigrams of patients with ILD is due to considerably increased inflammatory activity in the lungs. We retrospectively analyzed relationships between NHS and established biomarkers of disease severity in patients with ILD. Among 81 consecutive non-smoking patients with ILD (mean age, 63 years) who had been hospitalized between April 2009 and October 2011, we selected 52 who had been assessed by (67)Ga scintigraphy. We then evaluated relationships between NHS and blood biomarkers, pulmonary function and high-resolution computed tomography (HRCT). Among these 52 patients, 10 showed idiopathic pulmonary fibrosis and 42 had other ILD. Multivariate analysis with stepwise variable selection, serum surfactant protein (SP)-A (OR (odds ratio), 1.026; 95%CI (confidence interval), 1.003–1.050; P = 0.024) and inflammation index calculated from HRCT findings (OR, 1.358; 95%CI, 1.079–1.709; P = 0.009) were significant predictors of an NHS. Serum SP-A offered 85% sensitivity and 75% specificity for predicting NHS at an optimal cut-off of 45.8 ng/mL. Serum SP-A concentrations correlated positively with inflammation index (r = 0.344, P = 0.015). In conclusion, serum SP-A might serve as a surrogate biomarker for predicting an NHS in patients with ILD.