1. Field of the Invention
This invention relates to a method for classifying and counting white blood cells, erythroblasts, and bacteria in body fluids by means of an automated hematology analyzer. More particularly, this invention relates to a method for simultaneously differentiating and counting white blood cell populations, erythroblasts, and bacteria in body fluids by means of multi-angle light scatter, fluorescence, and triple triggering circuitry in a three-dimensional space.
2. Discussion of the Art
Examination of various body fluids is critical for the diagnosis of bacterial meningitis, bacterial pneumonia or lung abscess, infection of the peritoneal cavity, and septic arthritis. The conventional method of analyzing body fluids in order to determine the presence of a bacterial infection, which involves dilution of biological samples, counting cells by means of a hemocytometer, preparing cell cultures, Gram staining, and microscopic examination, is tedious, time-consuming, and labor-intensive, and some clinical cases, such as bacterial meningitis, require immediate treatment because an untreated case can be lethal. Thus, the ability to analyze body fluids on a rapid hematology analyzer would be extremely useful.
Analysis of most body fluids drawn from hospitalized patients must be carried out in the hospital as soon as possible because such body fluids are not very stable and can be expected to deteriorate within approximately two hours. Cerebrospinal fluid can be expected to deteriorate within one hour. See, for example, Body Fluids: Laboratory examination of amniotic, cerebrospinal, seminal, serous, & synovial fluids: a text book atlas/C. Kjeldsberg and J. Knight, eds. 3rd ed. ASCP Press, 1993, incorporated herein by reference. Thus, analyzing body fluids rapidly on an automated hematology analyzer would be desirable in hospital laboratories.
A number of manufacturers of hematology analyzers have systems that use the analysis of body fluids for cell counting. The Beckman-Coulter LH 750 hematology analyzer uses VCS technology (Volume by impedance, Complexity by radio-frequency, and laser light Scatter) for analysis of white blood cell differential. However, VCS technology cannot discriminate signals generated by bacterial cells from signals generated by other cell debris. The Bayer ADVIA® 2120 hematology analyzer uses myelo-peroxidase staining and light scatter to differentiate white blood cells. In the basophil channel, also known as the Lobularity/Nuclear density channel, a hypotonic surfactant solution is used to strip the cytoplasmic membrane from all leukocytes, except basophils. Neither the myeloperoxidase channel nor the basophil channel of the ADVIA® 2120 hematology analyzer is capable of distinguishing the signals generated by bacteria from signals generated by erythroblast nuclei or other cell debris.
The Sysmex XE-2100 hematology analyzer uses forward light scatter and side light scatter for counting white blood cells and nuclear staining, and side light scatter and fluorescence for differential analysis. However, the analyzer cannot distinguish the small noise signals generated by cell debris from those generated by bacteria. U.S. Pat. No. 5,325,168 describes a method and apparatus for analyzing cells in urine using both light scatter for determining size and fluorescence for determining differential DNA-staining intensity. This patent does not disclose how signals generated by small bacteria can be distinguished from noise signals generated by cell debris or from erythroblast nuclei. The cytograms of light scatter vs. fluorescence, i.e., FIGS. 14A, 14B, and 14C of U.S. Pat. No. 5,325,168, show no noticeable separation of noise signals from small bacterial signals.
To resolve the problems stated above, a rapid analysis of body fluids by means of an automated hematology analyzer, available in most clinical laboratories, is highly desirable to save the lives of infected patients by the rapid diagnosis of the medical condition of the patients and the subsequent treatment of the patients.