This document provides materials and methods for identifying and quantifying AIM polypeptides in a sample using mass spectrometry techniques. For example, methods of using mass spectrometry to identify and quantify AIM polypeptides in a serum sample are provided. In some cases, quantification of AIM polypeptides can be used to diagnose and/or treat patients having a disease or disorder characterized by altered (e.g., increased or decreased) AIM polypeptide levels.