Chronic kidney disease is associated with an increased risk of end-stage chronic renal disease, cardiovascular diseases and death; therefore, it is necessary since early phases of the disease to make a diagnosis. For this purpose, there are available a lot of equations for estimating glomerular filtration rates, which are based on serum creatinine concentration. Although creatinine is not the ideal analyte to estimate the glomerular filtration rate, it will continue in use until there is a massive availability of other markers, such as cystatin C. For this reason, clinical laboratories must provide results with high standards of quality control, and thus, they must measure serum creatinine with methods previously standardized according to any of the reference measurement procedures. The aim of this module is to review since early stages the chronic kidney disease diagnosis through serum creatinine measurement and glomerular filtration rate estimation.