<unk>  performed by the fingerstick method, using an Abbott Cell-Dyn 1700 automated analyzer The sample is collected by drawing<unk>  into a tube<unk> aining an anticoagulant—typically EDTA—to stop its natural clotting. The<unk>  is usually taken from a vein, but when this is difficult it may be collected from capillaries by a fingerstick, or by a heelprick in babies. Testing is typically performed on an automated analyzer, but manual techniques such as a<unk>  smear examination or manual hematocrit test can be used to investigate abnormal results. Cell<unk> s and hemoglobin measurements are performed manually in laboratories lacking access to automated instruments. Automated On board the analyzer, the sample is agitated to evenly distribute the cells, then diluted and partitioned into at least two channels, one of which is used to<unk>  red<unk>  cells and platelets, the other to<unk>  white<unk>  cells and determine the hemoglobin concentration. Some instruments measure hemoglobin in a separate channel, and additional channels may be used for differential white<unk>  cell<unk> s, reticulocyte<unk> s and specialized measurements of platelets. The cells are suspended in a fluid stream and their properties are measured as they flow past sensors in a technique known as flow cytometry. Hydrodynamic focusing may be used to isolate individual cells so that more accurate results can be obtained: the diluted sample is injected into a stream of low-pressure fluid, which causes the cells in the sample to line up in single file through laminar flow. Sysmex XT-alt=CBC samples in a rack, waiting to be run on a bench-top analyzer alt=Schematic of the<unk> er principle. A particle suspended in a conductive medium passes through an aperture, causing an increase in impedance To measure the hemoglobin concentration, a reagent chemical is added to the sample to destroy (lyse) the red cells in a channel separate from that used for red<unk>  cell<unk> s. On analyzers that perform white<unk>  cell<unk> s in the same channel as hemoglobin measurement, this permits white<unk>  cells to be<unk> ed more easily. Hematology analyzers measure hemoglobin using spectrophotometry and are based on the linear relationship between the absorbance of light and the amount of hemoglobin present. Chemicals are used to convert different forms of hemoglobin, such as oxyhemoglobin and carboxyhemoglobin, to one stable form, usually cyanmethemoglobin, and to create a permanent colour change. The absorbance of the resulting colour, when measured at a specific wavelength—usually 540 nanometres—corresponds with the concentration of hemoglobin. Sensors<unk>  and identify the cells in the sample using two main principles: electrical impedance and light scattering. Impedance-based cell<unk> ing operates on the<unk> er principle: cells are suspended in a fluid carrying an electric current, and as they pass through a small opening (an aperture), they cause decreases in current because of their poor electrical conductivity. The amplitude of the voltage pulse generated as a cell crosses the aperture correlates with the amount of fluid displaced by the cell, and thus the cell's volume, while the total number of pulses correlates with the number of cells in the sample. The distribution of cell volumes is plotted on a histogram, and by setting volume thresholds based on the typical sizes of each type of cell, the different cell populations can be identified and<unk> ed. In light scattering techniques, light from a laser or a tungsten-halogen lamp is directed at the stream of cells to collect information about their size and structure. Cells scatter light at different angles as they pass through the beam, which is detected using photometers. Forward scatter, which refers to the amount of light scattered along the beam's axis, is mainly caused by diffraction of light and correlates with cellular size, while side scatter (light scattered at a 90-degree angle) is caused by reflection and refraction and provides information about cellular complexity. Radiofrequency-based methods can be used in combination with impedance. These techniques work on the same principle of measuring the interruption in current as cells pass through an aperture, but since the high-frequency RF current penetrates into the cells, the amplitude of the resulting pulse relates to factors like the relative size of the nucleus, the nucleus's structure, and the amount of granules in the cytoplasm. Small red cells and cellular debris, which are similar in size to platelets, may interfere with the platelet<unk> , and large platelets may not be<unk> ed accurately, so some analyzers use additional techniques to measure platelets, such as fluorescent staining, multi-angle light scatter and monoclonal antibody tagging. Most analyzers directly measure the average size of red<unk>  cells, which is called the mean cell volume (MCV), and calculate the hematocrit by multiplying the red<unk>  cell<unk>  by the MCV. Some measure the hematocrit by comparing the total volume of red<unk>  cells to the volume of<unk>  sampled, and derive the MCV from the hematocrit and red<unk>  cell<unk> . The hemoglobin concentration, the red<unk>  cell<unk>  and the hematocrit are used to calculate the average amount of hemoglobin within each red<unk>  cell, the mean corpuscular hemoglobin (MCH); and its concentration, the mean corpuscular hemoglobin concentration (MCHC). Another calculation, the red<unk>  cell distribution width (RDW), is derived from the standard deviation of the mean cell volume and reflects variation in cellular size. alt=A scatter plot displaying many differently coloured clusters, labelled with the type of white<unk>  cell they correspond to. After being treated with reagents, white<unk>  cells form three distinct peaks when their volumes are plotted on a histogram. These peaks correspond roughly to populations of granulocytes, lymphocytes, and other mononuclear cells, allowing a three-part differential to be performed based on cell volume alone. More advanced analyzers use additional techniques to provide a five- to seven-part differential, such as light scattering or radiofrequency analysis, or using dyes to stain specific chemicals inside cells—for example, nucleic acids, which are found in higher concentrations in immature cells or myeloperoxidase, an enzyme found in cells of the myeloid lineage. Basophils may be<unk> ed in a separate channel where a reagent destroys other white cells and leaves basophils intact. The data collected from these measurements is analyzed and plotted on a scattergram, where it forms clusters that correlate with each white<unk>  cell type. Another approach to automating the differential<unk>  is the use of digital microscopy software, which uses artificial intelligence to classify white<unk>  cells from photomicrographs of the<unk>  smear. The cell images are displayed to a human operator, who can manually re-classify the cells if necessary. Most analyzers take less than a minute to run all the tests in the<unk> . Because analyzers sample and<unk>  many individual cells, the results are very precise. However, some abnormal cells may not be identified correctly, requiring manual review of the instrument's results and identification by other means of abnormal cells the instrument could not categorize. Point-of-care testing Point-of-care testing refers to tests conducted outside of the laboratory setting, such as at a person's bedside or in a clinic. This method of testing is faster and uses less<unk>  than conventional methods, and does not require specially trained personnel, so it is useful in emergency situations and in areas with limited access to resources. Commonly used devices for point-of-care hematology testing include the HemoCue, a portable analyzer that uses spectrophotometry to measure the hemoglobin concentration of the sample, and the i-STAT, which derives a hemoglobin reading by estimating the concentration of red<unk>  cells from the conductivity of the<unk> . Hemoglobin and hematocrit can be measured on point-of-care devices designed for<unk>  gas testing, but these measurements sometimes correlate poorly with those obtained through standard methods. There are simplified versions of hematology analyzers designed for use in clinics that can provide a<unk>  and differential. Manual alt=Diagram of the manual hematocrit test showing the fraction of red<unk>  cells measured as 0.46. The tests can be performed manually when automated equipment is not available or when the analyzer results indicate that further investigation is needed. Automated results are flagged for manual<unk>  smear review in 10–25% of cases, which may be due to abnormal cell populations that the analyzer cannot properly<unk> , internal flags generated by the analyzer that suggest the results could be inaccurate, or numerical results that fall outside set thresholds. To investigate these issues,<unk>  is spread on a microscope slide, stained with a Romanowsky stain, and examined under a microscope. The appearance of the red and white<unk>  cells and platelets is assessed, and qualitative abnormalities are reported if present. Changes in the appearance of red<unk>  cells can have considerable diagnostic significance—for example, the presence of sickle cells is indicative of sickle cell disease, and a high number of fragmented red<unk>  cells (schistocytes) requires urgent investigation as it can suggest a microangiopathic hemolytic anemia. In some inflammatory conditions and in paraprotein disorders like multiple myeloma, high levels of protein in the<unk>  may cause red<unk>  cells to appear stacked together on the smear, which is termed rouleaux. Some parasitic diseases,
Complete blood count
Lipid profile
Glycated hemoglobin
Hematocrit
Absolute neutrophil count
Erythrocyte sedimentation rate
Comprehensive metabolic panel
Red blood cell indices