To confirm efficiency of the designed enz-PADs for a complete elimination of endogenous creatine in the R1 zone, creatine was spiked into the standard or urine sample, and the assay recoveries were studied. As shown in Table S.2 (Supplementary data), the results show that 1 mg dL1 creatine did not significantly interfere with the proposed enz-PADs. This implies that enzymes in R1 of enz-PADs can completely eliminate the endogenous creatine up to 10 mg dL1 from undiluted urine samples. In general, urine creatine can be found in the range of 0–40 mg/day and 0–80 mg/day in males and in females, respectively [42]. If the average excreted urine volume is 1.5 L/day, the creatine concentration should be 0– 2.7 mg dL1 and 0–5.3 mg dL1 in males and in females, respectively. Therefore, the urine creatine levels do not interfere with the enzymatic reactions utilised in the proposed enz-PADs for creatinine determination.