Diagnostic and Prognostic Plasma Biomarkers for Idiopathic Pneumonia Syndrome after Hematopoietic Cell Transplantation

Idiopathic pneumonia syndrome (IPS) is a noninfectious pulmonary complication after hematopoietic cell transplantation (HCT) and is difficult to diagnose. In 41 patients with IPS, we evaluated 6 candidate proteins in plasma samples at day 7 post-HCT and at onset of IPS to identify potential diagnostic or prognostic biomarkers for IPS. Samples at similar times from 162 HCT recipients without documented infections and 37 HCT recipients with respiratory viral pneumonia served as controls. In multivariable models, a combination of Stimulation-2 (ST2; odds ratio [OR], 2.8; P < .001) and IL-6 (OR, 1.4; P = .025) was the best panel for distinguishing IPS at diagnosis from unaffected controls, whereas tumor necrosis factor receptor 1 (TNFR1; OR, 2.9; P = .002) was the best marker when comparing patients with IPS and viral pneumonia. The areas under the curve of the receiver operating characteristic (ROC) curves for discriminating between IPS and unaffected controls at day 7 post-HCT were .8 for ST2, .75 for IL-6, and .68 for TNFR1. Using estimated sensitivity and specificity values from cutoffs determined with the ROC analysis (cutoff level: ST2, 21 ng/mL; IL-6, 61 pg/mL; TNFR1, 3421 pg/mL), we calculated positive predictive values (PPV) for a range of estimated population prevalence values of IPS. Among the 3 markers, ST2 showed the highest PPV for IPS occurrence. Based on an assumed prevalence of 8%, a positive ST2 test increased likelihood of IPS to 50%. We conclude that a prospective validation study is warranted to determine whether a plasma biomarker panel can aid the noninvasive diagnosis and prognosis of IPS.