Extracting and concentrating particles from a first fluid sample includes: providing the first fluid sample to a fluid exchange module of a microfluidic device, providing a second fluid sample to the fluid exchange module, in which the first fluid sample and the second fluid sample are provided under conditions such that particle-free portions of the first fluid sample are shifted, and an inertial lift force causes the particles in the first fluid sample to cross streamlines and transfer into the second fluid sample; passing the second fluid sample containing the transferred particles to a particle concentration module under conditions such that particle-free portions of the second fluid sample are shifted, and such that the particles within the second fluid sample are focused to a streamline within the particle concentration module.