You should try RBC lysis before analysis. You can get good RBC lysis reagent by BD (BD Pharm Lyse), eBioscience (1X RBC Lysis Buffer) or Thermo Fisher (ACK Lysing Buffer). You can also make your own RBC lysis buffer (150 mM NH4Cl, 10mM, 0.1mM Na2EDTA).

Sir, I'll be processing the intact RBC's. So lysing them won't serve the purpose. 

Sorry I thought you wanted to analyse immune cells in blood. In that case 

Try adding some dextran 40 to your media at about 30mg/L. Heparin can cause RBC aggregation so don't use it in the media that you use in the microfluidic device. You can wash your RBCs in PBS twice and resuspend in PBS with dextran 40. You could also try increasing the shear in the device as well (higher flow rate or smaller dimension in part of the fluid path) to disaggregate the cells. RBCs often aggregate in low shear environments.

Thank you Prof. Andre  I'll try this protocol

Try to wash flow-chamber  (before measurements) by buffer that supplemented with 0.5-1.0 % of albumin.

   Thank you Prof.Gregory.  I'll try this.