A blood analyzer comprising: a specimen preparation section for preparing, by using a blood sample obtained from a subject, a measurement specimen that is used to measure a white blood cell count among CBC measurement items in a CBC measurement mode; and a measurement section for obtaining at least forward scattered light intensities and fluorescence light intensities from blood cells contained in the measurement specimen prepared by the specimen preparation section by irradiating the measurement specimen with light; characterized by: a controller including a memory under control of a processor, the memory storing instructions enabling the processor to carry out operations comprising: classifying blood cells contained in the measurement specimen into at least white blood cells and blood cells suspected to be PLT-related abnormal blood cells, based on the forward scattered light intensities and the fluorescence light intensities obtained by the measurement section; obtaining distribution data of the white blood cells and distribution data of the blood cells suspected to be PLT-related abnormal blood cells; counting the white blood cells contained in the blood sample, based on the distribution data of the white blood cells; determining presence or absence of the PLT-related abnormal blood cells in the blood sample, based on the distribution data of the blood cells suspected to be PLT-related abnormal blood cells; and outputting, when determining that the PLT-related abnormal blood cells are present, a display that prompts measurement of the blood sample to be performed in a platelet measurement mode capable of obtaining information about platelets. a specimen preparation section for preparing, by using a blood sample obtained from a subject, a measurement specimen that is used to measure a white blood cell count among CBC measurement items in a CBC measurement mode; and a measurement section for obtaining at least forward scattered light intensities and fluorescence light intensities from blood cells contained in the measurement specimen prepared by the specimen preparation section by irradiating the measurement specimen with light; characterized by: a controller including a memory under control of a processor, the memory storing instructions enabling the processor to carry out operations comprising: classifying blood cells contained in the measurement specimen into at least white blood cells and blood cells suspected to be PLT-related abnormal blood cells, based on the forward scattered light intensities and the fluorescence light intensities obtained by the measurement section; obtaining distribution data of the white blood cells and distribution data of the blood cells suspected to be PLT-related abnormal blood cells; counting the white blood cells contained in the blood sample, based on the distribution data of the white blood cells; determining presence or absence of the PLT-related abnormal blood cells in the blood sample, based on the distribution data of the blood cells suspected to be PLT-related abnormal blood cells; and outputting, when determining that the PLT-related abnormal blood cells are present, a display that prompts measurement of the blood sample to be performed in a platelet measurement mode capable of obtaining information about platelets. classifying blood cells contained in the measurement specimen into at least white blood cells and blood cells suspected to be PLT-related abnormal blood cells, based on the forward scattered light intensities and the fluorescence light intensities obtained by the measurement section; obtaining distribution data of the white blood cells and distribution data of the blood cells suspected to be PLT-related abnormal blood cells; counting the white blood cells contained in the blood sample, based on the distribution data of the white blood cells; determining presence or absence of the PLT-related abnormal blood cells in the blood sample, based on the distribution data of the blood cells suspected to be PLT-related abnormal blood cells; and outputting, when determining that the PLT-related abnormal blood cells are present, a display that prompts measurement of the blood sample to be performed in a platelet measurement mode capable of obtaining information about platelets.