The precise determination of serum microRNA entails clear distinction between the presence of endogenous target in biological samples before spike recovery and the actual concentration delivered through spike additions. Here we propose an endogenous blank partitioning approach for the determination of serum miR-18a in terms of the nanoporous-gold Y-shaped electrochemical biosensing method. The fundamental issue is if three spiked levels of serum human targets can be translated into blank contribution, target recovery, concentration bias, and repeatability measures. The experimental record features three additional concentrations of miR-18a of 100 fmol L−1, 1 pmol L−1, and 10 pmol L−1, combined with a serum blank of tenfold dilution, namely 24.165 fmol L−1. Upon subtracting the blank concentration, the obtained values became 95.415 fmol L−1, 1034.945 fmol L−1, and 10480.525 fmol L−1. Correspondingly, the percentage recoveries were estimated as 95.41%, 103.49%, and 104.81%, while the relative standard deviations were 1.81%, 2.19%, and 4.01%. Blank contributions accounted for 24.17% of the added concentration and 20.21% of the measured amount in case of the lowest level, whereas for the two higher levels they were reduced to 2.42% / 2.28% and 0.24% / 0.23%, respectively.