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Complete Blood Count (CBC)

The complete blood count (CBC) includes: hemoglobin, hematocrit, red blood cell (RBC) count, white blood cell (WBC) count, RBC indices, platelet count, and red cell distribution width (RDW). Hemoglobin, WBC count, RBC count, mean corpuscular volume (MCV), and platelet count are measured electronically by an automated hematology analyzer. Hematocrit, mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC) and RDW are calculated.

Modern cell counters measure the number of RBCs within a given blood volume by electrical impedance. RBC count is usually expressed as the number of RBCs per microliter or liter.

Hemoglobin concentration is measured by converting hemoglobin to hemiglobincyanide and spectrophotometrically measuring its light absorption at 540 nm.

Hematocrit is the percentage of whole blood volume represented by packed red blood cells. Automated cell counters calculate hematocrit by multiplying RBC count and MCV.

Mean cell volume (MCV) is a measure of the mean size of RBCs. Individual RBC volumes are measured directly by electrical impedance. The values are plotted on a histogram that is used to calculate mean cell volume. MCV is useful in classifying anemia a normocytic, microcytic or macrocytic.

Mean corpuscular hemoglobin (MCH) is the average hemoglobin content of a single RBC. It is the calculated by dividing hemoglobin by the RBC count.

Mean corpuscular hemoglobin concentration (MCHC) is the average red cell hemoglobin concentration expressed as a percent. It is calculated by multiplying hemoglobin by 100 and dividing the product by the hematocrit. Elevated MCHC can be caused by spherocytosis, hyponatremia, cold agglutinin, lipemia or strongly discolored plasma.

Red cell distribution width (RDW) is a measure of variability in the size of RBCs. RDW is calculated by dividing the standard deviation from the RBC volume histogram by MCV. Increased variability in RBC size is called anisocytosis.

An automated CBC with differential white blood cell count can determine 32 different hematological parameters.  Automated cell counters incorporate a method for flagging white blood cell (WBC), red blood cell (RBC) and platelet abnormalities. The flagged abnormalities prompt a medical scientist to perform a manual peripheral smear review and differential to verify the abnormality flagged as well as allow identification of additional morphological abnormalities.

An automated cell counter can be programmed to flag the following abnormalities:

WBC Abnormalities

  • Abnormal lymphocytes/lymphoblasts
  • Atypical lymphocytes
  • Basophilia
  • Blasts
  • Eosinophilia
  • Immature granulocytes
  • Left shift
  • Leukocytopenia
  • Leukocytosis
  • Lymphopenia
  • Monocytosis
  • Neutropenia
  • Neutrophilia
  • Nucleated red blood cell abnormal scatter
  • WBC abnormal scatter

 RBC Abnormalities

  •  Fragments (schistocytes)

 Platelet Abnormalities

  • Platelet abnormal scattergram
  • Platelet clumps
  • Thrombocytopenia
  • Thrombocytosis

If specimens are flagged for review, the following RBC morphological abnormalities, if present, are reported by the clinical laboratory scientist: polychromasia, acanthocytes (spur cells), ovalocytes (elliptocytes), spherocytes, sickle cells (drepanocytes), target cells (codocytes), schistocytes, stomatocytes, rouleaux and basophilic stippling. RBC inclusions (Howell Jolly bodies), granulocyte abnormalities (toxic granulation, Dohle bodies, Pelger Huet, hypersegmented polymorphonuclear leukocytes) and giant platelets are also reported if present. 

Slides with newly identified blasts, prolymphocytes, plasma cells or unusual WBC and RBC morphology are submitted by the clinical laboratory scientist to a pathologist for review.  In addition, healthcare providers may request a pathologist review of a peripheral blood smear if further morphological review is deemed clinically necessary.  In these cases, the indication for the pathologist review should be clearly stated on the requisition form.

Adult reference ranges and critical values are:


Parameter Reference Range Critical Value
WBC 4,000 - 11,000/uL


>50,000/uL (if first diagnosis)

>100,000/uL (known patient)


Males      4.31 - 5.84 mil/uL

Females  4.00 - 5.00  mil/uL


Males       13.0 - 17.0 g/dL

Females   12.0 - 15. 0 g/dL

<6.0 g/dL

Males        40 - 50%

Females    36 - 45%


>70% neonates up to 2 mos

>60% all others

MCV 80 - 99 fL  
MCH 27 - 34 pg  
MCHC 32 - 36%  
Reticulocytes 0.4 – 1.8%  
Immature Reticulocyte Fraction 0.0 – 0.16  
RDW 11.5-14.5%  
Platelet Count 140,000 - 400,000/uL


>1 million/uL

Mean Platelet Volume 9.4 – 12.3 fL  
Immature Platelet Fraction 1.1 – 7.1%  


Reference range for the WBC differential count is:


White Cell Relative Absolute
Bands 0 - 14% N/A
Neutrophils 45 - 78% 1.7 - 6.8 th/uL
Lymphocytes 15 - 47% 1.0 - 3.3 th/uL
Monocytes 0 - 12% 0.2 -0.9 th/uL
Eosinophils 0 - 7% 0.0 - 0.4 th/uL
Basophils 0 - 2% 0.0 - 0.2 th/uL


Specimen requirement is one lavender top (EDTA) tube.

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