Complete blood count

A complete blood count (CBC), also known as a full blood count (FBC) or full haemogram (FHG), is a set of medical laboratory tests that provide information about the cells in a person's blood. The CBC indicates the counts of white blood cells, red blood cells and platelets, the concentration of hemoglobin, and the hematocrit (the volume percentage of red blood cells). The red blood cell indices, which indicate the average size and hemoglobin content of red blood cells, are also reported, and a white blood cell differential, which counts the different types of white blood cells, may be included.

The CBC is often carried out as part of a medical assessment and can be used to monitor health or diagnose diseases. The results are interpreted by comparing them to reference ranges, which vary with sex and age. Conditions like anemia and thrombocytopenia are defined by abnormal complete blood count results. The red blood cell indices can provide information about the cause of a person's anemia such as iron deficiency and vitamin B12 deficiency, and the results of the white blood cell differential can help to diagnose viral, bacterial and parasitic infections and blood disorders like leukaemia. Not all results falling outside of the reference range require medical intervention.

The CBC is usually performed by an automated hematology analyzer, which counts cells and collects information on their size and structure. The concentration of hemoglobin is measured, and the red blood cell indices are calculated from measurements of red blood cells and hemoglobin. Manual tests can be used to independently confirm abnormal results. Approximately 10–25% of samples require a manual blood smear review, The complete blood count evaluates the three cellular components of blood. Some medical conditions, such as anemia or thrombocytopenia, are defined by marked increases or decreases in blood cell counts.

The CBC is often used to screen for diseases as part of a medical assessment. It is also called for when a healthcare provider suspects a person has a disease that affects blood cells, such as an infection, a bleeding disorder, or some cancers. People who have been diagnosed with disorders that may cause abnormal CBC results or who are receiving treatments that can affect blood cell counts may have a regular CBC performed to monitor their health, The results may indicate a need for a blood or platelet transfusion.

The complete blood count has specific applications in many medical specialties. It is often performed before a person undergoes surgery to detect anemia, ensure that platelet levels are sufficient, and screen for infection, as well as after surgery, so that blood loss can be monitored. In emergency medicine, the CBC is used to investigate numerous symptoms, such as fever, abdominal pain, and shortness of breath, and to assess bleeding and trauma. Blood counts are closely monitored in people undergoing chemotherapy or radiation therapy for cancer, because these treatments suppress the production of blood cells in the bone marrow and can produce severely low levels of white blood cells, platelets and hemoglobin. Regular CBCs are necessary for people taking some psychiatric drugs, such as clozapine and carbamazepine, which in rare cases can cause a life-threatening drop in the number of white blood cells (agranulocytosis). Because anemia during pregnancy can result in poorer outcomes for the mother and her baby, the complete blood count is a routine part of prenatal care; and in newborn babies, a CBC may be needed to investigate jaundice or to count the number of immature cells in the white blood cell differential, which can be an indicator of sepsis.

The complete blood count is an essential tool of hematology, which is the study of the cause, prognosis, treatment, and prevention of diseases related to blood. The results of the CBC and smear examination reflect the functioning of the hematopoietic system—the organs and tissues involved in the production and development of blood cells, particularly the bone marrow. For example, a low count of all three cell types (pancytopenia) can indicate that blood cell production is being affected by a marrow disorder, and a bone marrow examination can further investigate the cause. Abnormal cells on the blood smear might indicate acute leukaemia or lymphoma,

The reference ranges for the complete blood count represent the range of results found in 95% of apparently healthy people. This is particularly likely if such results are only slightly outside the reference range, if they are consistent with previous results, or if there are no other related abnormalities shown by the CBC. When the test is performed on a relatively healthy population, the number of clinically insignificant abnormalities may exceed the number of results that represent disease. For this reason, professional organizations in the United States, United Kingdom and Canada recommend against pre-operative CBC testing for low-risk surgeries in individuals without relevant medical conditions. Repeated blood draws for hematology testing in hospitalized patients can contribute to hospital-acquired anemia and may result in unnecessary transfusions. The blood 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 blood smear examination or manual hematocrit test can be used to investigate abnormal results. Cell counts 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 count red blood cells and platelets, the other to count white blood cells and determine the hemoglobin concentration. Some instruments measure hemoglobin in a separate channel, and additional channels may be used for differential white blood cell counts, reticulocyte counts 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.

thumb|[[Sysmex XT-4000i automated hematology analyzer|alt=CBC samples in a rack, waiting to be run on a bench-top analyzer]]

thumb|The Coulter principle—the transient current drop is proportional to the particle volume|alt=Schematic of the Coulter 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 blood cell counts. On analyzers that perform white blood cell counts in the same channel as hemoglobin measurement, this permits white blood cells to be counted 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 count and identify the cells in the sample using two main principles: electrical impedance and light scattering. Impedance-based cell counting operates on the Coulter 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 counted.

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.

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 count, and large platelets may not be counted accurately, so some analyzers use additional techniques to measure platelets, such as fluorescent staining, multi-angle light scatter and monoclonal antibody tagging. Another calculation, the red blood cell distribution width (RDW), is derived from the standard deviation of the mean cell volume and reflects variation in cellular size.

thumb|left|upright=1.3|Example of a white blood cell differential scattergram: differently coloured clusters indicate different cell populations|alt=A scatter plot displaying many differently coloured clusters, labelled with the type of white blood cell they correspond to.

After being treated with reagents, white blood 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 myeloperoxidase, an enzyme found in cells of the myeloid lineage. Basophils may be counted 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 blood cell type. which uses artificial intelligence to classify white blood cells from photomicrographs of the blood 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 complete blood count. 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. Hemoglobin and hematocrit can be measured on point-of-care devices designed for blood 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 complete blood count and differential.

Manual

thumb|upright=0.6|left|Manual determination of hematocrit. The blood has been centrifuged, separating it into red blood cells and plasma.|alt=Diagram of the manual hematocrit test showing the fraction of red blood 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. or numerical results that fall outside set thresholds. The appearance of the red and white blood cells and platelets is assessed, and qualitative abnormalities are reported if present. Changes in the appearance of red blood 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 blood 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 blood may cause red blood cells to appear stacked together on the smear, which is termed rouleaux. Some parasitic diseases, such as malaria and babesiosis, can be detected by finding the causative organisms on the blood smear, and the platelet count can be estimated from the blood smear, which is useful if the automated platelet count is inaccurate. This gives the percentage of each type of white blood cell, and by multiplying these percentages by the total number of white blood cells, the absolute number of each type of white cell can be obtained. Manual counting is subject to sampling error because so few cells are counted compared with automated analysis,

The hematocrit can performed manually by filling a capillary tube with blood, centrifuging it, and measuring the percentage of the blood that consists of red blood cells. or severe leukocytosis (a highly elevated white blood cell count, which interferes with red blood cell measurements by causing white blood cells to be counted as red cells). Manual cell counts are labour-intensive and inaccurate compared to automated methods, so they are rarely used except in laboratories that do not have access to automated analyzers. Sometimes a stain is added to the diluent that highlights the nuclei of white blood cells, making them easier to identify. Manual platelet counts are performed in a similar manner, although some methods leave the red blood cells intact. Using a phase-contrast microscope, rather than a light microscope, can make platelets easier to identify. The manual red blood cell count is rarely performed, as it is inaccurate and other methods such as hemoglobinometry and the manual hematocrit are available for assessing red blood cells; but if it is necessary to do so, red blood cells can be counted in blood that has been diluted with saline.

Hemoglobin can be measured manually using a spectrophotometer or colorimeter. To measure hemoglobin manually, the sample is diluted using reagents that destroy red blood cells to release the hemoglobin. Other chemicals are used to convert different types of hemoglobin to one form, allowing it to be easily measured. The solution is then placed in a measuring cuvette and the absorbance is measured at a specific wavelength, which depends on the type of reagent used. A reference standard containing a known amount of hemoglobin is used to determine the relationship between the absorbance and the hemoglobin concentration, allowing the hemoglobin level of the sample to be measured.

In rural and economically disadvantaged areas, available testing is limited by access to equipment and personnel. At primary care facilities in these regions, testing may be limited to examination of red cell morphology and manual measurement of hemoglobin, while more complex techniques like manual cell counts and differentials, and sometimes automated cell counts, are performed at district laboratories. Regional and provincial hospitals and academic centres typically have access to automated analyzers. Where laboratory facilities are not available, an estimate of hemoglobin concentration can be obtained by placing a drop of blood on a standardized type of absorbent paper and comparing it to a colour scale.

Quality control

Automated analyzers have to be regularly calibrated. Most manufacturers provide preserved blood with defined parameters and the analyzers are adjusted if the results are outside defined thresholds. To ensure that results continue to be accurate, quality control samples, which are typically provided by the instrument manufacturer, are tested at least once per day. The samples are formulated to provide specific results, and laboratories compare their results against the known values to ensure the instrument is functioning properly. For laboratories without access to commercial quality control material, an Indian regulatory organization recommends running patient samples in duplicate and comparing the results. A moving average measurement, in which the average results for patient samples are measured at set intervals, can be used as an additional quality control technique. Assuming that the characteristics of the patient population remain roughly the same over time, the average should remain constant; large shifts in the average value can indicate instrument problems.

In addition to analyzing internal quality control samples with known results, laboratories may receive external quality assessment samples from regulatory organizations. While the purpose of internal quality control is to ensure that analyzer results are reproducible within a given laboratory, external quality assessment verifies that results from different laboratories are consistent with each other and with the target values. The expected results for external quality assessment samples are not disclosed to the laboratory. External quality assessment programs have been widely adopted in North America and western Europe, Logistical issues may make it difficult for laboratories in under-resourced areas to implement external quality assessment schemes.

Included tests

{| class="wikitable sortable mw-collapsible floatright" style="font-size: smaller; text-align: center; width: auto; table-layout: fixed;"

! Analyte

! Meaning

!WBC

|White blood cell concentration

!RBC

|Red blood cell concentration

!HGB

|Hemoglobin concentration

!HCT

|Hematocrit fraction

!MCV

|Mean cell volume

!MCH

|Mean corpuscular hemoglobin mass

!MCHC

| Mean corpuscular hemoglobin concentration

!RDW-CV

| Red blood cell volume distribution width calculated as a percentage

!RDW-SD

| Red blood cell volume distribution width at 20% histogram height

!PLT

|Platelet concentration

!MPV

|Mean platelet volume

!NEUT

|Neutrophil concentration and/or fraction

!LYMPH

|Lymphocyte concentration and/or fraction

!MONO

|Monocyte concentration and/or fraction

!EO

|Eosinophil concentration and/or fraction

!BASO

|Basophil concentration and/or fraction

!IG

|Immature granulocyte concentration and/or fraction

!NRBC

|Nucleated red blood cell concentration and/or fraction

The CBC measures the amounts of platelets and red and white blood cells, along with the hemoglobin and hematocrit values. Red blood cell indices—MCV, MCH and MCHC—which describe the size of red blood cells and their hemoglobin content, are reported along with the red blood cell distribution width (RDW), which measures the amount of variation in the sizes of red blood cells. A white blood cell differential, which enumerates the different types of white blood cells, may be performed, and a count of immature red blood cells (reticulocytes) is sometimes included.

Red blood cells, hemoglobin, and hematocrit

{| style="text-align:left; width:100%; font-size:85%; border: 1px solid grey"

|+ Sample CBC in microcytic anemia

! scope="col" | Analyte

! scope="col" | Result

! scope="col" | Normal range

! scope="row" | Red cell count

| 5.5 × 10<sup>12</sup>/L || 4.5–5.7

! scope="row" | White cell count

| 9.8 × 10<sup>9</sup>/L || 4.0–10.0

! scope="row" | Hemoglobin

| || 133–167

! scope="row" | Hematocrit

| 0.42 || 0.35–0.53

! scope="row" | MCV

| || 77–98

! scope="row" | MCH

| || 26–33

! scope="row" | MCHC

| || 330–370

! scope="row" | RDW

| 14.5% || 10.3–15.3

<div style="font-size:88%; line-height:1.4em; margin-top:0.3em;">An example of CBC results showing a low hemoglobin, MCV, MCH and MCHC. The person was anemic. The cause could be iron deficiency or a hemoglobinopathy.</div>

</div>

Red blood cells deliver oxygen from the lungs to the tissues and on their return carry carbon dioxide back to the lungs where it is exhaled. These functions are mediated by the cells' hemoglobin. The analyzer counts red blood cells, reporting the result in units of 10<sup>6</sup> cells per microlitre of blood (× 10<sup>6</sup>/μL) or 10<sup>12</sup> cells per litre (× 10<sup>12</sup>/L), and measures their average size, which is called the mean cell volume and expressed in femtolitres or cubic micrometres. Hemoglobin, measured after the red blood cells are lysed, is usually reported in units of grams per litre (g/L) or grams per decilitre (g/dL). Assuming that the red blood cells are normal, there is a constant relationship between hemoglobin and hematocrit: the hematocrit percentage is approximately three times greater than the hemoglobin value in g/dL, plus or minus three. This relationship, called the rule of three, can be used to confirm that CBC results are correct.

Two other measurements are calculated from the red blood cell count, the hemoglobin concentration, and the hematocrit: the mean corpuscular hemoglobin and the mean corpuscular hemoglobin concentration. These parameters describe the hemoglobin content of each red blood cell. The MCH and MCHC can be confusing; in essence the MCH is a measure of the average amount of hemoglobin per red blood cell. The MCHC gives the average proportion of the cell that is hemoglobin. The MCH does not take into account the size of the red blood cells whereas the MCHC does. Collectively, the MCV, MCH, and MCHC are referred to as the red blood cell indices. Another parameter is calculated from the initial measurements of red blood cells: the red blood cell distribution width or RDW, which reflects the degree of variation in the cells' size.

upright=1.2|left|thumb|[[Blood smear from a person with iron deficiency anemia, displaying characteristic red blood cell morphology. The red blood cells are abnormally small (microcytosis), have large areas of central pallor (hypochromia), and vary greatly in size (anisocytosis).|alt=See caption.]]

An abnormally low hemoglobin, hematocrit, or red blood cell count indicates anemia. Anemia is not a diagnosis on its own, but it points to an underlying condition affecting the person's red blood cells. Anemia reduces the blood's ability to carry oxygen, causing symptoms like tiredness and shortness of breath. If the hemoglobin level falls below thresholds based on the person's clinical condition, a blood transfusion may be necessary.

An increased number of red blood cells, leading to an increase in the hemoglobin and hematocrit, is called polycythemia. Dehydration or use of diuretics can cause a "relative" polycythemia by decreasing the amount of plasma compared to red cells. A true increase in the number of red blood cells, called absolute polycythemia, can occur when the body produces more red blood cells to compensate for chronically low oxygen levels in conditions like lung or heart disease, or when a person has abnormally high levels of erythropoietin, a hormone that stimulates production of red blood cells. In polycythemia vera, the bone marrow produces red cells and other blood cells at an excessively high rate.

Evaluation of red blood cell indices is helpful in determining the cause of anemia. If the MCV is low, the anemia is termed microcytic, while anemia with a high MCV is called macrocytic anemia. Anemia with a low MCHC is called hypochromic anemia. If anemia is present but the red blood cell indices are normal, the anemia is considered normochromic and normocytic. An elevated MCHC can also be a false result from conditions like red blood cell agglutination (which causes a false decrease in the red blood cell count, elevating the MCHC) or highly elevated amounts of lipids in the blood (which causes a false increase in the hemoglobin result).

Microcytic anemia is typically associated with iron deficiency, thalassemia, and anemia of chronic disease, while macrocytic anemia is associated with alcoholism, folate and B12 deficiency, use of some drugs, and some bone marrow diseases. Acute blood loss, hemolytic anemia, bone marrow disorders, and various chronic diseases can result in anemia with a normocytic blood picture. The MCV serves an additional purpose in laboratory quality control. It is relatively stable over time compared to other CBC parameters, so a large change in MCV may indicate that the sample was drawn from the wrong patient.

A low RDW has no clinical significance, but an elevated RDW represents increased variation in red blood cell size, a condition known as anisocytosis.

White blood cells

{| style="border: 1px solid grey;" role="presentation"

|+ Sample CBC in chronic myeloid leukaemia

|- style="vertical-align:top;"

{| style="text-align:left; width:12em; font-size:85%;"

! scope="col" | Analyte

! scope="col" | Result

! scope="row" | White cell count

| × 10<sup>9</sup>/L

! scope="row" | Hemoglobin

| 116 g/L

! scope="row" | Hematocrit

| 0.349 L/L

! scope="row" | MCV

| 89.0 fL

! scope="row" | Platelet count

| × 10<sup>9</sup>/L

{| style="text-align:left; width:14em; font-size:85%;"

! scope="col" | Analyte

! scope="col" | Result

! scope="row" | Neutrophils

| 48%

! scope="row" | Lymphocytes

| 3%

! scope="row" | Monocytes

| 4%

! scope="row" | Eosinophils

| 3%

! scope="row" | Basophils

! scope="row" | Band neutrophils

! scope="row" | Metamyelocytes

! scope="row" | Myelocytes

! scope="row" | Blast cells

The white blood cell and platelet counts are markedly increased, and anemia is present. The differential count shows basophilia and the presence of band neutrophils, immature granulocytes and blast cells.</div>

</div>

White blood cells defend against infections and are involved in the inflammatory response. A high white blood cell count, which is called leukocytosis, often occurs in infections, inflammation, and states of physiologic stress. It can also be caused by diseases that involve abnormal production of blood cells, such as myeloproliferative and lymphoproliferative disorders. A decreased white blood cell count, termed leukopenia, can lead to an increased risk of acquiring infections, and occurs in treatments like chemotherapy and radiation therapy and many conditions that inhibit the production of blood cells. Sepsis is associated with both leukocytosis and leukopenia. The total white blood cell count is usually reported in cells per microlitre of blood (/μL) or 10<sup>9</sup> cells per litre (× 10<sup>9</sup>/L). Some instruments report the number of immature granulocytes, which is a classification consisting of precursors of neutrophils; specifically, promyelocytes, myelocytes and metamyelocytes. Other cell types are reported if they are identified in the manual differential.

Differential results are useful in diagnosing and monitoring many medical conditions. For example, an elevated neutrophil count (neutrophilia) is associated with bacterial infection, inflammation, and myeloproliferative disorders, Neutropenia can also be caused by some congenital disorders and may occur transiently after viral or bacterial infections in children. People with severe neutropenia and clinical signs of infection are treated with antibiotics to prevent potentially life-threatening disease.

An increased number of band neutrophils—young neutrophils that lack segmented nuclei—or immature granulocytes is termed left shift and occurs in sepsis and some blood disorders, but is normal in pregnancy. An elevated lymphocyte count (lymphocytosis) is associated with viral infection and lymphoproliferative disorders like chronic lymphocytic leukaemia; elevated monocyte counts (monocytosis) are associated with chronic inflammatory states; and the eosinophil count is often increased (eosinophilia) in parasitic infections and allergic conditions. An increased number of basophils, termed basophilia, can occur in myeloproliferative disorders like chronic myeloid leukaemia and polycythemia vera. The presence of some types of abnormal cells, such as blast cells or lymphocytes with neoplastic features, is suggestive of a hematologic malignancy.

Platelets

thumb|left|alt=See caption.|Blood film of [[essential thrombocythemia. Platelets are visible as small purple structures.]]

Platelets play an essential role in clotting. When the wall of a blood vessel is damaged, platelets adhere to the exposed surface at the site of injury and plug the gap. Simultaneous activation of the coagulation cascade results in the formation of fibrin, which reinforces the platelet plug to create a stable clot. A low platelet count, known as thrombocytopenia, may cause bleeding if severe. It can occur in individuals who are undergoing treatments that suppress the bone marrow, such as chemotherapy or radiation therapy, or taking certain drugs, such as heparin, that can induce the immune system to destroy platelets. Thrombocytopenia is a feature of many blood disorders, like acute leukaemia and aplastic anemia, as well as some autoimmune diseases. If the platelet count is extremely low, a platelet transfusion may be performed. Thrombocytosis, meaning a high platelet count, may occur in states of inflammation or trauma, as well as in iron deficiency, and the platelet count may reach exceptionally high levels in people with essential thrombocythemia, a rare blood disease. 10<sup>3</sup> cells per microlitre , or 10<sup>9</sup> cells per litre The immature platelet fraction (IPF) or reticulated platelet count is reported by some analyzers and provides information about the rate of platelet production by measuring the number of immature platelets in the blood.

Other tests

Reticulocyte count

thumb|alt=Microscopic image of red blood cells stained blue.|Red blood cells stained with [[new methylene blue: the cells containing dark blue structures are reticulocytes.]]

Reticulocytes are immature red blood cells, which, unlike the mature cells, contain RNA. A reticulocyte count is sometimes performed as part of a complete blood count, usually to investigate the cause of a person's anemia or evaluate their response to treatment. Anemia with a high reticulocyte count can indicate that the bone marrow is producing red blood cells at a higher rate to compensate for blood loss or hemolysis, When people with nutritional anemia are given nutrient supplementation, an increase in the reticulocyte count indicates that their body is responding to the treatment by producing more red blood cells. Hematology analyzers perform reticulocyte counts by staining red blood cells with a dye that binds to RNA and measuring the number of reticulocytes through light scattering or fluorescence analysis. The test can be performed manually by staining the blood with new methylene blue and counting the percentage of red blood cells containing RNA under the microscope. The reticulocyte count is expressed as an absolute number

Some instruments measure the average amount of hemoglobin in each reticulocyte; a parameter that has been studied as an indicator of iron deficiency in people who have conditions that interfere with standard tests. The immature reticulocyte fraction (IRF) is another measurement produced by some analyzers which quantifies the maturity of reticulocytes: cells that are less mature contain more RNA and thus produce a stronger fluorescent signal. This information can be useful in diagnosing anemias and evaluating red blood cell production following anemia treatment or bone marrow transplantation.

Nucleated red blood cells

thumb|left|alt=See caption.|Blood smear from a newborn baby, showing a few nucleated red cells

During their formation in bone marrow, and in the liver and spleen in fetuses, red blood cells contain a cell nucleus, which is usually absent in the mature cells that circulate in the bloodstream. Nucleated red blood cells are normal in newborn babies, but when detected in children and adults, they indicate an increased demand for red blood cells, which can be caused by bleeding, some cancers and anemia.

Other parameters

Advanced hematology analyzers generate novel measurements of blood cells which have shown diagnostic significance in research studies but have not yet found widespread clinical use. have been studied as potential markers for blood disorders, bacterial infections and malaria. Analyzers that use myeloperoxidase staining to produce differential counts can measure white blood cells' expression of the enzyme, which is altered in various disorders. Because these parameters are often specific to particular brands of analyzers, it is difficult for laboratories to interpret and compare results.

! scope="col" | Test

! scope="col" | Units

! scope="col" | Adult

! scope="col" | Paediatric

(4–7 years old)

! scope="col" | Neonate

(0–1 days old)

! scope="row" | WBC

|× 10<sup>9</sup>/L

|3.6–10.6

|5.0–17.0

|9.0–37.0

! scope="row" | RBC

|× 10<sup>12</sup>/L

|4.00–5.20

|4.10–6.10

! scope="row" | HGB

|g/L

|102–152

|165–215

! scope="row" | HCT

|L/L

|0.36–0.46

|0.48–0.68

! scope="row" | MCV

|fL

|80–100

|78–94

|95–125

! scope="row" | MCH

|pg

|26–34

|23–31

|30–42

! scope="row" | MCHC

|g/L

|320–360

|300–340

! scope="row" | RDW

|11.5–14.5

|elevated