Abstract: The invention concerns a device and a method for concentrating pathogenic germs potentially present in blood products or derivatives and for detecting said germs comprising the following steps: (a) subjecting a sample of said blood product to a blood cell aggregating treatment, (b) eliminating the aggregates formed at step (a) by passing the treated sample over a first filter allowing through the contaminating germs but not the cell aggregates, (c) selectively lyzing the residual cells of the filtrate obtained at step (b), (d) recuperating the contaminating germs by passing the lysate of step (c) over a second filter to detect the contaminating germs possibly trapped.