Complete blood count

“Blood count” redirects here. For the Billy Strayhorncomposition, see Blood Count.

A complete blood count (CBC), also known as a com-plete blood cell count, full blood count (FBC), or fullblood exam (FBE), is a blood panel requested by adoctor or other medical professional that gives informa-tion about the cells in a patient’s blood. A scientist or labtechnician performs the requested testing and providesthe requesting medical professional with the results of theCBC.Blood counts of various types have been used for clinicalpurposes since the 19th century. Automated equipmentto carry out complete blood counts was developed in the1950s and 1960s.[1]

The cells that circulate in the bloodstream are gen-erally divided into three types: white blood cells(leukocytes), red blood cells (erythrocytes), and platelets(thrombocytes). Abnormally high or low counts may in-dicate the presence of many forms of disease, and henceblood counts are amongst the most commonly performedblood tests in medicine, as they can provide an overviewof a patient’s general health status. A CBC is routinelyperformed during annual physical examinations in somejurisdictions.

1 Medical uses

Complete blood counts are done to monitor overallhealth, to screen for some diseases, to confirm a diag-nosis of some medical conditions, to monitor a medicalcondition, and to monitor changes in the body caused bymedical treatments.[2]

For patients who need blood transfusion, a blood countmay be used to get data which would help plan an amountof treatment.[3] In such cases, the person should have onlyone blood count for the day, and the transfusion of redblood cells or platelets should be planned based on that.[3]Multiple blood draws and counts throughout the day arean excessive use of phlebotomy and can lead to unnec-essary additional transfusions, and the extra unnecessarytreatment would be outside of medical guidelines.[3]

CBC being performed in a hospital using an Abbott Cell-Dyn1700 automatic analyzer.

2 Procedure

Aphlebotomist collects the sample through venipuncture,drawing the blood into a test tube containing ananticoagulant (EDTA, sometimes citrate) to stop it fromclotting. The sample is then transported to a laboratory.Sometimes the sample is drawn off a finger prick usinga Pasteur pipette for immediate processing by an auto-mated counter.In the past, counting the cells in a patient’s blood wasperformed manually, by viewing a slide prepared with asample of the patient’s blood (a blood film, or periph-eral smear) under a microscope. Presently, this processis generally automated by use of an automated analyzer,with only approximately 10–20% of samples now beingexamined manually.

2.1 Automated blood count

All blood counts include a CBC count and leukocytedifferential count (LDC), but modern analyzers providemuch more in addition.[4]

The blood is well mixed (though not shaken) and placedon a rack in the analyzer. This instrument has flow cells,photometers and apertures that analyze different elementsin the blood. The cell counting component counts thenumbers and types of different cells within the blood. Theresults are printed out or sent to a computer for review.Blood counting machines aspirate a very small amountof the specimen through narrow tubing followed by anaperture and a laser flow cell. Laser eye sensors countthe number of cells passing through the aperature, andcan identify them; this is flow cytometry. The two main

1

2 2 PROCEDURE

Complete blood count performed by an automated analyser. Dif-ferentials missing.

sensors used are light detectors and electrical impedance.The instrument measures the type of blood cell by ana-lyzing data about the size and aspects of light as they passthrough the cells (called front and side scatter). Other in-struments measure different characteristics of the cells tocategorize them.Because an automated cell counter samples and countsso many cells, the results are very precise. However, cer-tain abnormal cells in the blood may not be identified cor-rectly, requiring manual review of the instrument’s resultsand identification of any abnormal cells the instrumentcould not categorize.In addition to counting, measuring and analyzing redblood cells, white blood cells and platelets, auto-mated hematology analyzers also measure the amountof hemoglobin in the blood and within each red bloodcell. This is done by adding a diluent that lyses the cellswhich is then pumped into a spectro-photometric mea-suring cuvette. The change in color of the lysate equatesto the hemoglobin content of the blood. This informa-tion can be very helpful to a physician who, for example,is trying to identify the cause of a patient’s anemia. If thered cells are smaller or larger than normal, or if there isa lot of variation in the size of the red cells, this data canhelp guide the direction of further testing and expeditethe diagnostic process so patients can get the treatmentthey need quickly.

2.2 Manual blood count

Hemocytometers (counting chambers that hold a speci-fied volume of diluted blood and divide it with grid lines)are used to calculate the number of red and white cellsper litre of blood. (The dilution and grid lines are neededbecause there are far too many cells without those aids.)To identify the numbers of different white cells, a bloodfilm is made, and a large number of white blood cells (atleast 100) are counted. This gives the percentage of cells

Manual blood counts use a light microscope, usually with a spe-cialized microscope slide, which is called a hemocytometer.

This shows the view through the microscope of the specializedhemocytometer slide. The built-in grid simplifies counting cellsby helping the technician keep track of which cells have alreadybeen counted.

that are of each type. By multiplying the percentage withthe total number of white blood cells, the absolute num-ber of each type of white cell can be obtained.Manual counting is useful in cases where automated ana-lyzers cannot reliably count abnormal cells, such as thosecells that are not present in normal patients and are onlyseen in peripheral blood with certain haematological con-ditions. Manual counting is subject to sampling error be-cause so few cells are counted compared with automatedanalysis.Medical technologists examine blood film via a micro-scope for some CBCs, not only to find abnormal whitecells, but also because variation in the shape of red cellsis an important diagnostic tool. Although automatedanalysers give fast, reliable results regarding the num-ber, average size, and variation in size of red blood cells,they do not detect cells’ shapes. Also, some normal pa-tients’ platelets will clump in EDTA anticoagulated blood,which causes automatic analyses to give a falsely lowplatelet count. The person viewing the slide in these caseswill see clumps of platelets and can estimate if there are

3.4 Hematocrit 3

low, normal, or high numbers of platelets.

3 Included tests

A scanning electron microscope (SEM) image of normal circu-lating human blood. One can see red blood cells, several knobbywhite blood cells including lymphocytes, a monocyte, a neu-trophil, and many small disc-shaped platelets.

A complete blood count will normally include:

3.1 White cells

• Total white blood cells — All the white cell typesare given as a percentage and as an absolute numberper litre.[5]

3.2 Red cells

• Total red blood cells — The number of red cells isgiven as an absolute number per litre.[5] Iron defi-ciency Anemia shows up as a Low RBC count.

• LOINC codes for Whole Blood RBC Count-ing

3.3 Hemoglobin

• Hemoglobin – The amount of hemoglobin in theblood, expressed in grams per decilitre.[5] A lowlevel of Hemoglobin is a sign of anemia.

• LOINC codes for this test(Note: not all thecodes in the search result are suitable for thistest.)

3.4 Hematocrit

• Hematocrit or packed cell volume (PCV) – This isthe fraction of whole blood volume that consists ofred blood cells.[5]

• Red blood cell indices[6]

3.5 MCV

• Mean corpuscular volume (MCV) – the average vol-ume of the red cells, measured in femtolitres.[5]Anemia is classified as microcytic or macrocytic ifthe MCV value is above or below the expected nor-mal range; anemias are classified as normocytic ifthe MCV is within the expected range. Other con-ditions that can affect MCV include thalassemia,reticulocytosis, alcoholism, chemotherapy, VitaminB12 deficiency, and/or Folic acid deficiency.

3.6 MCH

• Mean corpuscular hemoglobin (MCH) – the aver-age amount of hemoglobin per red blood cell, inpicograms.[5]

3.7 MCHC

• Mean corpuscular hemoglobin concentration(MCHC) – the average concentration of hemoglobinin the cells.

3.8 RDW

• Red blood cell distribution width (RDW) – the vari-ation in cellular volume of the RBC population.

A complete blood count with differential/platelet will alsoinclude:

• Neutrophil granulocytes — May indicate bacterialinfection. May also be raised in acute viral infec-tions. Because of the segmented appearance of thenucleus, neutrophils are sometimes referred to as“segs.” The nucleus of less mature neutrophils is notsegmented, but has a band or rod-like shape. Lessmature neutrophils — those that have recently beenreleased from the bone marrow into the bloodstream— are known as “bands” or “stabs”. Stab is a Ger-man term for rod.[7]

4 7 EXTERNAL LINKS

• Lymphocytes — Higher with some viral infectionssuch as glandular fever and. Also raised in chroniclymphocytic leukemia (CLL). Can be decreased byHIV infection. In adults, lymphocytes are the sec-ond most common WBC type after neutrophils. Inyoung children under age 8, lymphocytes are morecommon than neutrophils.[7]

• Monocytes — May be raised in bacterial infec-tion, tuberculosis, malaria, Rocky Mountain spottedfever, monocytic leukemia, chronic ulcerative colitisand regional enteritis [7]

• Eosinophil granulocytes— Increased in parasitic in-fections, asthma, or allergic reaction.

• Basophil granulocytes — May be increased in bonemarrow related conditions such as leukemia orlymphoma.[7]

A manual count will also give information about othercells that are not normally present in peripheral blood,but may be released in certain disease processes.

3.9 Platelets

• Platelet numbers are given, as well as informationabout their size and the range of sizes in the blood.[5]

• Mean platelet volume (MPV) – a measurement ofthe average size of platelets.

4 Results

An example report format for a complete blood count.Note that test names, measurement units and referenceranges may vary between countries and laboratories. Pa-tient results should always be interpreted using the unitsand reference ranges from the laboratory that producedthe results.

5 Interpretation

Certain disease states are defined by an absolute increaseor decrease in the number of a particular type of cell inthe bloodstream. For example:Many disease states are heralded by changes in the bloodcount:

• Leukocytosis can be a sign of infection

• Thrombocytopenia can result from drug toxicity

• Pancytopenia is generally referred to as the result ofdecreased production from the bone marrow, and isa common complication of cancer chemotherapy

6 References[1] Verso, ML (May 1962). “The Evolution of Blood Count-

ing Techniques”. Read at a meeting of the Section of theHistory of Medicine, First Australian Medical Congress8: 149–58. doi:10.1017/s0025727300029392. PMC1033366. PMID 14139094. Retrieved 9 September2013.

[2] Mayo Clinic (14 February 2014). “Complete blood count(CBC) Why it’s done - Tests and Procedures”. may-oclinic.org. Retrieved 29 July 2014.

[3] American Association of Blood Banks (24 April 2014),“Five Things Physicians and Patients Should Question”,Choosing Wisely: an initiative of the ABIM Foundation(American Association of Blood Banks), retrieved 25 July2014, which cites

• Napolitano, LM; Kurek, S; Luchette, FA; Cor-win, HL; Barie, PS; Tisherman, SA; Hebert,PC; Anderson, GL; Bard, MR; Bromberg, W;Chiu, WC; Cipolle, MD; Clancy, KD; Diebel,L; Hoff, WS; Hughes, KM; Munshi, I; Nayduch,D; Sandhu, R; Yelon, JA; American College ofCritical Care Medicine of the Society of Criti-cal Care, Medicine; Eastern Association for theSurgery of Trauma Practice Management, Work-group (Dec 2009). “Clinical practice guideline:red blood cell transfusion in adult trauma andcritical care.”. Critical Care Medicine 37 (12):3124–57. doi:10.1097/CCM.0b013e3181b39f1b.PMID 19773646.

[4] Buttarello, M; Plebani, M (Jul 2008). “Automatedblood cell counts: state of the art.”. Ameri-can journal of clinical pathology 130 (1): 104–16. doi:10.1309/EK3C7CTDKNVPXVTN. PMID18550479.

[5] David C., Dugdale (19March 2012). “CBC: MedlinePlusMedical Encyclopedia”. MedlinePlus. United States Na-tional Library of Medicine. Retrieved 29 July 2014.

[6] “RBC indices”. MedlinePlus: U.S. National Library ofMedicine. Retrieved 1 June 2013.

[7] “Complete Blood count with Differential”. RbCeus.com.2013. Retrieved 2014-11-21.

7 External links• Blood Groups and Red Cell Antigens. Free onlinebook at NCBI Bookshelf ID: NBK2261

• Complete Blood Count - Lab Tests Online

5

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