There is increasing evidence that, in addition to their presence, the propensity of circulating tumour cells to form multi-cellular clusters bears significant information about both cellular resistance to chemotherapy and overall prognosis. We present a novel two-stage, stopped-flow, continuous centrifugal sedimentation strategy to measure the size distributions of events (defined here as cells or clusters thereof) in a blood sample. After off-chip removal of red blood cells, healthy white blood cells are sequestered by negative-immunocapture. The purified events are then resolved along a radially inclined rail featuring a series of gaps with increasing width, each connected to a designated outer collection bin. The isolation of candidate events independent of target-specific epitopes is successfully demonstrated for HL60 (EpCAM positive) and sk-mel28 (EpCAM negative) cells using identical protocols and reagents. The propensity to form clusters was quantified for a number of cell lines, showing a negligible, moderate or elevated tendency towards cluster formation. We show that the occupancy distribution of the collection bins closely correlates with the range of cluster sizes intrinsic to the specific cell line.