Filtration Parameters Influencing Circulating Tumor Cell Enrichment from Whole Blood

Abstract

Filtration can achieve circulating tumor cell (CTC) enrichment from blood. Key parameters such as flow-rate, applied pressure, and fixation, vary largely between assays and their influence is not well understood. Here, we used a filtration system, to monitor these parameters and determine their relationships. Whole blood, or its components, with and without spiked tumor cells were filtered through track-etched filters. We characterize cells passing through filter pores by their apparent viscosity; the viscosity of a fluid that would pass with the same flow. We measured a ratio of 5·10 4 :10 2 :1 for the apparent viscosities of 15 μm diameter MDA-231 cells, 10 μm white cells and 90 fl red cells passing through a 5 μm pore. Fixation increases the pressure needed to pass cells through 8 μm pores 25-fold and halves the recovery of spiked tumor cells. Filtration should be performed on unfixed samples at a pressure of ∼10 mbar for a 1 cm 2 track-etched filter with 5 μm pores. At this pressure MDA-231 cells move through the filter in 1 hour. If fixation is needed for sample preservation, a gentle fixative should be selected. The difference in apparent viscosity between CTC and blood cells is key in optimizing recovery of CTC. © 2013 Coumans et al.