Assessing the potential usefulness of IGF-related peptides and adiponectin for predicting disease risk

Insulin-like growth factors (IGF), their binding proteins and adiponectin have been investigated as potential blood-based biomarkers for a variety of diseases. Before these circulating proteins can be considered as biomarkers, their variation within and between individuals and between published studies must be critically assessed. The purpose of this study was to use the D-value to predict the potential usefulness of IGF-related peptides and adiponectin as biomarkers for the diagnosis of colorectal cancer (CRC).Intra- and inter-individual variation of total IGF-I and -II, IGF binding protein 1 (IGFBP-1), -2 and -3 and adiponectin, was examined in 10 healthy subjects over a 5 week period. This data was analysed in conjunction with previous publications to provide a D-value, which is a theoretical value that identifies the usefulness of the analyte individually and as a panel, as a biomarker for CRC.A single measurement of total IGF-I and -II, and adiponectin provided a reproducible representation of their circulating concentrations. The D-value for total IGF-II and IGFBP-3 were 0.5 and 0.47, respectively, which corresponded to area under the curve (AUC) values of 64 and 63%. Combining these analytes into a panel only slightly improved the D-value to 0.63 (AUC was 67%).Although serum levels of total IGF-I, total IGF-II and IGFBP-3 are stable and reproducible, the D-value calculations indicate that they have limited importance when used as biomarkers of CRC.