CST3 and diabetes mellitus: Even though serum sphingomyelin showed consistent association with a wide range of kidney function indicators, serum creatinine may be a biased indicator of kidney function in the setting of diabetes and therefore our results should be confirmed also with other filtration markers, such as cystatin C. Metabolomic analysis enabled us to assess the total serum sphingomyelin level, mainly carried in the circulation by LDL-cholesterol [41].