where D is the average cell diameter and VCD is the viable cell density, assuming a spherical shape of the cells. Bioreactor titer samples were prepared by centrifugation (3200 g for 10 min) and 0.22 μm filtered. Harvest titer samples were directly analyzed without further sample preparation. Process titers were determined using a protein A affinity high performance liquid chromatography device (PA‐HPLC, Waters, Milford, Massachusetts, USA). Cell debris was measured using an optical density (OD) measurement (Spectronic Genesys 10 Bio, Thermo Electron Corporation, Waltham, Massachusetts, USA). Therefore, bioreactor samples were centrifuged (3200 g for 10 min) and measured at 600 nm against a 0.22 μm filtered reference sample.