Since early detection of poor coronary collateralization may have clinical relevance as cardiovascular mortality associated with coronary artery disease with or without diabetes or chronic kidney disease is significantly higher partly due to impaired coronary collateralization [1–3], it is pertinent to examine the relationship between serum cystatin C and coronary collateralization in patients with stable coronary artery disease. This evidence concerns the gene CST3 and coronary artery disorder.