A hematology analyzer comprising: a) a flow cell; b) a light source for directing light to said flow cell; c) a plurality of detectors (32, 34, 3 6, 38) for detecting a plurality of optical characteristics of a blood sample passing through said flow cell; and d) a data analysis workstation comprising a processor, wherein the processor comprises a physical computer-readable medium programmed with instructions that, when executed by the processor, cause the hematology analyzer to: i) pass the blood sample through the flow cell and direct the light source to the flow cell to generate a plurality of optical data using the plurality of detectors (32, 34, 36, 38); ii) analyze the optical data to determine one or more values for the blood sample, wherein the value is selected from the group comprising: a lymphocyte geometric distance, wherein the lymphocyte geometric distance is based on a mean axial light loss measurement and a mean intermediate angle scatter measurement of a cell in the blood sample that is classified as a lymphocyte, lymphocyte box count ratio, wherein lymphocyte box count ratio comprises a value that is the inverse of the ratio of: the number of cells classified as lymphocytes in the blood sample as defined by a predetermined ALL limit and a predetermined IAS limit; divided by the number of cells classified as lymphocytes in the blood sample as defined by a predetermined ALL limit that is adjacent to the ALL limit in and a predetermined IAS limit that is adjacent to the IAS limit in, or a lymphocyte depolarized side scatter value; and iii) calculate the difference between each value and a reference criterion that is based on data obtained from a plurality of reference samples, wherein if the value differs from the reference criterion by a predetermined amount, then the blood sample is flagged as containing lysis-resistant red blood cells (rRBCs) or fragile white blood cells (fWBCs). a) a flow cell; b) a light source for directing light to said flow cell; c) a plurality of detectors (32, 34, 3 6, 38) for detecting a plurality of optical characteristics of a blood sample passing through said flow cell; and d) a data analysis workstation comprising a processor, wherein the processor comprises a physical computer-readable medium programmed with instructions that, when executed by the processor, cause the hematology analyzer to: i) pass the blood sample through the flow cell and direct the light source to the flow cell to generate a plurality of optical data using the plurality of detectors (32, 34, 36, 38); ii) analyze the optical data to determine one or more values for the blood sample, wherein the value is selected from the group comprising: a lymphocyte geometric distance, wherein the lymphocyte geometric distance is based on a mean axial light loss measurement and a mean intermediate angle scatter measurement of a cell in the blood sample that is classified as a lymphocyte, lymphocyte box count ratio, wherein lymphocyte box count ratio comprises a value that is the inverse of the ratio of: the number of cells classified as lymphocytes in the blood sample as defined by a predetermined ALL limit and a predetermined IAS limit; divided by the number of cells classified as lymphocytes in the blood sample as defined by a predetermined ALL limit that is adjacent to the ALL limit in and a predetermined IAS limit that is adjacent to the IAS limit in, or a lymphocyte depolarized side scatter value; and iii) calculate the difference between each value and a reference criterion that is based on data obtained from a plurality of reference samples, wherein if the value differs from the reference criterion by a predetermined amount, then the blood sample is flagged as containing lysis-resistant red blood cells (rRBCs) or fragile white blood cells (fWBCs). i) pass the blood sample through the flow cell and direct the light source to the flow cell to generate a plurality of optical data using the plurality of detectors (32, 34, 36, 38); ii) analyze the optical data to determine one or more values for the blood sample, wherein the value is selected from the group comprising: a lymphocyte geometric distance, wherein the lymphocyte geometric distance is based on a mean axial light loss measurement and a mean intermediate angle scatter measurement of a cell in the blood sample that is classified as a lymphocyte, lymphocyte box count ratio, wherein lymphocyte box count ratio comprises a value that is the inverse of the ratio of: the number of cells classified as lymphocytes in the blood sample as defined by a predetermined ALL limit and a predetermined IAS limit; divided by the number of cells classified as lymphocytes in the blood sample as defined by a predetermined ALL limit that is adjacent to the ALL limit in and a predetermined IAS limit that is adjacent to the IAS limit in, or a lymphocyte depolarized side scatter value; and iii) calculate the difference between each value and a reference criterion that is based on data obtained from a plurality of reference samples, wherein if the value differs from the reference criterion by a predetermined amount, then the blood sample is flagged as containing lysis-resistant red blood cells (rRBCs) or fragile white blood cells (fWBCs).