Creatinine level in urine is a key factor to monitor kidney performance. The use of an alternative microfluidic platform based on cellulose substrates is an interesting option to integrate sample treatment, creatinine recognition by ionophore extraction chemistry and quantification by color measurement through consumer electronics imaging devices. The inclusion of ionophore extraction chemistry based on aryl-substituted calix[4]pyrrole synthetic receptor on 8.7 mm long cotton thread permit the sample treatment, optical recognition of creatinine and their quantification by smartphone running app in unfiltered urine samples diluted 1:100 ratio. The device shows a short response time, 30 s, to creatinine over a wide dynamic range (from 1.6 × 10−6 to 5 × 10^–2 M) with precision between 2.9–4.3%. The low interference level of representative species in urine is studied and justified by density functional theory (DFT) calculations.