The potential of photoacoustic imaging for detecting red blood cell (RBC) aggregation is explored. Enhanced aggregation is observed in disorders such as diabetes impairing oxygen release into tissue. Simultaneous measurements of aggregation and oxygenation levels cannot be made using current tools. Photoacoustic detection of aggregation and assessment of oxygen saturation was investigated. A theoretical and experimental model of aggregation was developed using human and porcine RBCs. Frequency-domain analysis of the PA signals was used to derive the spectral slope and midband fit of the normalized power spectra for various hematorit and aggregation conditions. Oxygen saturation was assessed using multiple wavelengths of illumination. The experimental spectral slope (~0.3 dB/MHz) for non-aggregated samples agreed with the theory decreasing with increasing aggregate size. The midband fit increased by ~5 dB when the aggregate size reached the largest level while the oxygen saturation increased by > 20%. These results suggest that photoacoustic-radio-frequency-spectroscopic-parameters have the potential to monitor RBC aggregation and oxygenation level.