1. A blood cell analyzer comprising: a mixing chamber that mixes a sample and a reagent to prepare a measurement specimen for classifying white blood cells, wherein the reagent hemolyzes red blood cells contained in the sample and fluorescently stains nucleic acid in white blood cells contained in the sample; a piercer that aspirates the sample from a sample container and discharges the aspirated sample into the mixing chamber; a flow cell; a laser that emits light to the measurement specimen flowing through the flow cell; a fluorescence light detector that detects fluorescence light emitted from each blood cell in the measurement specimen; first and second scattered light detectors that detect side scattered light and forward scattered light from each blood cell in the measurement specimen; a processor; and a non-transitory computer-readable recording medium storing computer instructions that, when executed by the processor, cause the processor to: receive, from the fluorescence light detector and the first and second scattered light detectors, a set of intensity signals representing an intensity of the detected fluorescence light and intensities of the side scattered light and the forward scattered light for each blood cell in the measurement specimen; position a coordinate of a respective set of the intensity signals in a single 3-D coordinate system having three coordinate dimensions representing the intensities of the fluorescent light and the side scattered light and the forward scattered light, wherein the coordinate of the respective set of the intensity signals is uniquely positioned in the single 3-D coordinate system according to the three intensity signals represented by the coordinate; and analyze spatial relationships among the coordinates of the sets of the intensity signals positioned in the single 3-D coordinate system and classify the coordinates of the sets of the intensity signals into at least four groups of the white blood cells and a group of neoplastic lymphocytes.