Complete Blood Count (CBC) in Practice

The number of red blood cells in a blood sample. Normal values vary by sex, with adult males typically having 5 ± 0.5 million/mm3 and females 4.3 ± 0.5 million/mm3.

A low RBC count or erythrocytopenia, can be caused by blood loss (trauma, surgery, internal bleeding) or impaired production (anemia, deficiency).

High RBC count (erythrocytosis) can be caused by conditions like polycythemia vera, smoking, or even living at high altitudes.

The ratio of red blood cells to the total volume of blood, expressed as a percentage.

Like RBC count, HCT levels can be elevated due to conditions like polycythemia vera or living at high altitudes. Low HCT levels usually reflect the same reasons as low RBC count levels.

The protein in red blood cells responsible for carrying oxygen. Normal range varies by age and sex.

The average size of a red blood cell. Normal range varies slightly by age.

A type of anemia that occurs when red blood cells are smaller than normal. Often seen in iron deficiency.

A type of anemia where red blood cells are normal size but there are less than normal. Often seen in blood loss.

A type of anemia where red blood cells are larger than normal. Can be caused by B12 deficiency.

The average amount of hemoglobin in a single red blood cell.

The concentration of hemoglobin in a given volume of packed red blood cells.

A type of anemia where red blood cells have a lower concentration of hemoglobin. Often seen in iron deficiency.

Automated blood cell counters can identify and reject samples with abnormal cells like nucleated red blood cells (NRBCs), myelocytes, promyelocytes, blasts, or atypical lymphocytes.

The presence of NRBCs can directly affect the accuracy of the white blood cell (WBC) count on some blood cell counters.

NRBCs are counted and reported as the number per 100 white blood cells. The correct WBC count is obtained by subtracting the number of NRBCs from the total nucleated count.

Automated instruments determine NRBCs by staining them with a nuclear dye and using fluorescence laser light scatter or flow cytometry to separate them from white blood cells (WBC) or a combination of impedance and cell volume.

A 'flag' in hematology is a signal to the operator that the analyzed data may have a significant abnormality. It requires confirmation by microscopic examination.

Automated blood cell counters measure hemoglobin (Hb) by a modification of the manual HiCN method with cyanide reagent. Hb, Hi, and HbCO are converted to HiCN, and the absorbance of the solution is measured at a specific wavelength.

The erythrocyte sedimentation rate (ESR) measures the rate at which red blood cells (erythrocytes) settle from the plasma. The sedimentation process is divided into three phases: aggregation, sedimentation, and packing.

The first phase of the ESR is the aggregation phase where erythrocytes form rouleaux. The second phase is the sedimentation phase where the aggregates fall out of solution. The last phase is the packing phase where the erythrocytes pack together tightly at the bottom of the tube.

Positively charged plasma proteins can neutralize the negative charge on erythrocytes, causing them to clump together.

Increased fibrinogen, an acute-phase protein, can enhance erythrocyte aggregation, leading to a higher ESR.

Low albumin levels can decrease ESR, as reduced albumin leads to less effective erythrocyte clustering.

Anemia, especially macrocytic anemia, often results in a higher ESR due to fewer erythrocytes and larger red blood cells.

Irregularly shaped erythrocytes, like in sickle cell anemia, don't clump as well as normal ones, leading to a low or even zero ESR.

A standardized test method for measuring the rate of erythrocyte sedimentation using EDTA-anticoagulated whole blood and a calibrated Westergren pipet.

Automated ESR methods, available since the 1990s, generally use a calibrated tube, and the ESR value is automatically determined.

A three-part differential count classifies white blood cells into three categories: granulocytes (large cells), lymphocytes (small cells), and monocytes (middle cells).

This method uses light scattering to analyze the size, shape, and granularity of cells. Forward scatter indicates cell size, sideward scatter reflects nuclear segmentation, and intermediate-angle scatter reveals cytoplasmic granules.

Automated blood cell counters use flow cytometry to differentiate white blood cells based on their physical characteristics. They can provide either a three-part or a five- to seven-part differential count.

Automated blood cell counters often analyze diluted whole blood where red cells are either lysed (broken down) or made transparent, allowing for better focus on white blood cells.

In the three-part differential, granulocytes (large cells) usually include eosinophils and basophils, but sometimes these are counted as monocytes instead.

Five- to seven-part differential counts provide a more detailed classification of white blood cells, including neutrophils, eosinophils, basophils, lymphocytes, monocytes, and sometimes immature cells.

Some three-part differentials use ratios to categorize white blood cells, like WBC-small cell ratio (lymphocytes), WBC-middle cell ratio (monocytes, eosinophils, basophils), and WBC-large cell ratio (neutrophils).

Automated counters with three-part differential capabilities can detect an increase in certain cell types like eosinophils and basophils, even though they don't count them individually.

Platelet count in adults typically ranges between 150-450x109/l. Children generally have higher counts. Elevated platelet count (thrombocytosis) may indicate various conditions like blood loss, infection, inflammation or malignancy. Conversely, a low platelet count (thrombocytopenia) suggests either peripheral consumption and destruction, or failure of platelet production.

A condition where the number of platelets in the blood is lower than normal. It can be caused by peripheral consumption (splenomegaly, immune, infection) or by failure of production in the bone marrow (aplastic anemia, leukemia).

An artificial lower platelet count due to platelet clumping in the blood sample. Often caused by the anticoagulant EDTA.

The volume occupied by platelets in the blood, typically expressed as a percentage. It's calculated by dividing the platelet count multiplied by the MPV by 10,000.

A measure of the average volume of platelets in the blood, expressed in femtoliters (fL). It's typically within the range of 7.2-11.7 fL.

An indicator of the variability in platelet size, expressed as a percentage. Increased PDW suggests platelet anisocytosis.

A measure of the percentage of larger circulating platelets (above 12 fL). It's typically between 15-35% and can indicate platelet activity.

The analysis of complete blood count (CBC) histogram that provides information about various disease processes even before further investigations. It can potentially reveal insightful patterns and clues.