IGF-Binding Protein-1 Levels Are Related to Insulin-Mediated Glucose Disposal and Are a Potential Serum Marker of Insulin Resistance : Response to van Haeften et al.

We appreciate the interest of van Haeflen et al. (1) in our article (2) concerning IGF-binding protein (IGFBP)-1 as a maker of insulin resistance in healthy nondiabetic subjects. In contrast to our study, they did not find a strong a correlation between insulin action as determined by the hyperinsulinemic clamp and levels of IGFBP-1. There are several possible explanations for the difference in results between their study and ours. First, they provided no direct information about the patients other than that they were not diabetic. They cite a reference concerning their study of insulin resistance in heart failure patients on various medications (3), and it would appear that these patients were the ones studied. In contrast to sick patients, we studied healthy nondiabetic individuals with a broad range of insulin sensitivity. Thus, the difference between the studies could be the difference in patient populations and/or the medications their patients were taking. We drew samples for IGFBP-1 between 7 a.m. and 9 a.m. in fasting subjects. It is unknown whether their patients were fasting when the protein was measured and at what times the samples were drawn. Since there is a diurnal variation for IGF-binding protein 1, it is possible that they drew samples at different times during the day, which would alter the results. Considering all these unknown variables, we believe it is not possible to compare our study with theirs.