Flow rates in a microfluidic device are modulated after performing serial dilutions by flow reduction channels that draw fluid from the main channel, thus reducing the flow rate. The reduction in flow rate and/or use of smaller dimension channels allow reduced reagent consumption. In addition, multiple flow reduction channels are used for multiple concentration measurements and for performing multiple assays simultaneously on a single sample. Also included are microfluidic devices and integrated systems for performing assays using serial dilutions, single pressure sources, multiple concentration measurements, and reduced reagent consumption. Devices comprising flow reduction channels are also used to suppress pressure perturbations from spontaneous injection.