Creatinine is the end product of creatine metabolism, which normally exists in serum and is eradicated from the blood circulation via glomerular filtration at a constant excretion rate [1,2]. Abnormal levels of creatinine in serum or urine indicate impaired kidney function, and creatinine has been accepted as a marker for monitoring the impact of treatment in haemodialysis patients [2]. Moreover, urinary creatinine concentration is widely used as an index for urine dilution [3] and as an internal standard for normalising the ratios of other urinary biomarkers, such as microalbumin [4], protein [5], cystatin-c [6], α-dicarbonyl compounds [7], and bisphenol A (BPA) [8].