A classifier and method for predicting or characterizing graft-versus-host disease in a patient after receiving a transplant of pluripotent hematopoietic stem cells or bone marrow. The classifier operates on mass-spectral data obtained from a blood-based sample of the patient and is configured as a combination of filtered mini-classifiers using a regularized combination method, such as logistic regression with extreme drop-out. The method also uses a “deep-MALDI” mass spectrometry technique in which the blood-based samples are subject to at least 100,000 laser shots in MALDI-TOF mass spectrometry in order to reveal greater spectral content and detect low abundance proteins circulating in serum associated with graft-versus-host disease.
