A method of performing rapid antimicrobial susceptibility testing for a pathogen in a biological sample obtained from a subject, the method comprising: (a) determining the presence and genus of a pathogen in a biological sample by (i) preparing an assay sample by contacting a first portion of the biological sample with magnetic particles, wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of an analyte associated with the pathogen; (ii) placing the assay sample in a device, the device comprising a support defining a well for holding the assay sample, and having an RF coil configured to detect a signal produced by exposing the assay sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (iii) exposing the assay sample to the bias magnetic field and the RF pulse sequence; (iv) following step (iii), measuring the signal produced by the assay sample; and (v) based on the results of step (iv), determining the presence and genus of the pathogen in the biological sample; (b) in parallel to step (a), incubating a second portion of the biological sample under conditions suitable for growth of the pathogen to form a pathogen culture; and (c) comparing the growth rate of a first aliquot of the pathogen culture in the presence of the antimicrobial agent to the growth rate of a second aliquot of the pathogen culture in the absence of the antimicrobial agent, thereby determining whether the pathogen is susceptible to the antimicrobial agent. (a) determining the presence and genus of a pathogen in a biological sample by (i) preparing an assay sample by contacting a first portion of the biological sample with magnetic particles, wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of an analyte associated with the pathogen; (ii) placing the assay sample in a device, the device comprising a support defining a well for holding the assay sample, and having an RF coil configured to detect a signal produced by exposing the assay sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (iii) exposing the assay sample to the bias magnetic field and the RF pulse sequence; (iv) following step (iii), measuring the signal produced by the assay sample; and (v) based on the results of step (iv), determining the presence and genus of the pathogen in the biological sample; (i) preparing an assay sample by contacting a first portion of the biological sample with magnetic particles, wherein the magnetic particles have binding moieties on their surfaces, the binding moieties operative to alter the specific aggregation of the magnetic particles in the presence of an analyte associated with the pathogen; (ii) placing the assay sample in a device, the device comprising a support defining a well for holding the assay sample, and having an RF coil configured to detect a signal produced by exposing the assay sample to a bias magnetic field created using one or more magnets and an RF pulse sequence; (iii) exposing the assay sample to the bias magnetic field and the RF pulse sequence; (iv) following step (iii), measuring the signal produced by the assay sample; and (v) based on the results of step (iv), determining the presence and genus of the pathogen in the biological sample; (b) in parallel to step (a), incubating a second portion of the biological sample under conditions suitable for growth of the pathogen to form a pathogen culture; and (c) comparing the growth rate of a first aliquot of the pathogen culture in the presence of the antimicrobial agent to the growth rate of a second aliquot of the pathogen culture in the absence of the antimicrobial agent, thereby determining whether the pathogen is susceptible to the antimicrobial agent.