Red blood cell aggregation is an important risk indicator of cardiovascular diseases, which can be quantified by dynamical parameters derived from a time-dependent light transmission profile (syllectogram). This study tests the hypothesis that inhibitory factors on the aggregation process of the blood could greatly alter the dynamical information provided by the syllectogram and highlights the possible limitations in utilizing time-dependent photometric methods for quantifying aggregation. The concept of $AI_{win}$ (aggregation index) that has been used in conventional aggregometers to determine the extent of aggregation within a 12-s standard time period was distinguished from AI (aggregation index) derived from the aggregating phase of syllectogram. Apparent time delays in shape recovery and aggregating phases were observed at high levels of aggregation inhibition (high medium viscosity) which accounted for the discrepancy between AI and $AI_{win}$. In the presence of a small shear (3 $s^{-1}$), this discrepancy diminished. Fractal analysis was used to validate the aggregation results obtained from the syllectogram. AI was found to better depict the extent of aggregation compared to $AI_{win}$.