A patient's health may be diagnosed by centrifuging blood samples in a transparent tube, which tube contains one or more bodies or groups of bodies such as floats, inserts, liposomes, or plastic beads of different densities. Each density-defined body carries analyte-capture binding materials such as antigens or antibodies, which are specific to an epitope, or other specific high affinity binding site on a target analyte which target analyte may be in the blood or other sample being tested; and the level of which analyte is indicative of the patient's health. At least one labeled binding material which is also specific to an epitope, or other specific high affinity binding site on the target analyte is added to the sample so as to form labeled binding material/analyte/body complexes in the sample. Upon centrifugation, the complexes will settle out in different areas in the tube according to the respective density of the body or bodies; and the degree of label emission of the complex layers can enable qualitative and/or quantitative analyses of the sample to be made. Unbound labeled binding materials will be separated from the complexed layers by the washing action of ascending or descending components of the sample during the centrifugation step. Unbound labeled binding material will thus not interfere with the analysis.