Our results are in agreement with previous studies showing that elevated YKL-40 levels are independently associated with the presence and extent of CAD. Moreover, in patients with MI even higher YKL-levels are documented. YKL-40 has also been found to be associated with all-cause as well as cardiovascular mortality not only in patients with stable CAD but also in the general population above 50 years of age without known diabetes or CAD. In patients with type 1 diabetes, increasing YKL-40 levels are seen with increasing levels of albuminuria as an expression of progressing vascular damages in the kidneys, suggesting that YKL-40 might be used as an early marker of CVD. However, the present findings do not support this hypothesis. The association between elevated IL-6 levels and myocardial perfusion SJN 2511 446859-33-2 defects in the present study are in accordance with a meta-analysis where IL-6 levels are associated with risk of CAD but the causality between IL-6 and CAD remains uncertain. In contrast to the single previous study also designed to examine hsCRP levels in patients referred to a MPI, the present study could not document elevated hsCRP levels in patients with myocardial perfusion defects. This divergence could be due to a significantly minor study population with a higher prevalence of men in the previous study but also due to a study population with less cardiovascular disease. Our findings regarding hsCRP and IL-6 are in accordance with a previous study where no association was found between levels of hsCRP or IL-6 and angiographic severity and major cardiac events. In the present study, the explanation for elevated IL-6 levels in men but not in women remains speculative, but might reflect some kind of local production in the heart. We did not find elevated MMP-9 levels in patients with myocardial perfusion defects although MMP-9 is known to destabilize the advanced atherosclerotic plaques and are seen with elevated concentrations in patients with increasing severity of ischemic symptoms. Beside the limitation of being a small-scale study, the foremost limitation is the lack of a pre-test likelihood analysis of the risk of CAD or an abnormal MPI in the study population. One could also dispute the relative high proportion of normal MPIs in this study but in comparison to other studies this is most likely due to the more selected group of participants with less co-morbidity. The advantage of having participants with less co-morbidity is that the NT-proBNP cut-off concentration as a predictor of a normal MPI is strengthened. Furthermore, the small number of participants above 70 years of age make statistical analyses of the influence of age on the predictive value of NT-proBNP obsolete.