A system and method for analyzing a sample of liquid having an NMR signal in response to a magnetic field for the presence of an analyte. Included is an NMR device having a testing section that is adapted to contain a liquid and apply a magnetic field to the liquid. A complex comprised of a conjugate having a field gradient bound to the analyte that is of sufficient magnitude to quench the NMR signal of the liquid when in the test section whereby the presence of the complex is determined by the absence of the NMR signal. The system and method also include a container having a binding agent therein that has an affinity for the analyte or foreign agent that is used to remove the foreign agent from a patient's blood or plasma. Blood or plasma is shunted through the container to remove or reduce the foreign agent by extracorporeal circulation.