1. Blood Tests

What types of cells are in blood and what do they do?

The three main cell types in blood are red blood cells (abbreviated RBCs, also called erythrocytes), white blood cells (abbreviated WBC, also called leukocytes) and platelets (abbreviated PLT). Red blood cells carry oxygen throughout the body, white blood cells are involved in immune responses, and platelets are involved in blood clotting.

What is the erythrocyte sedimentation rate (ESR)?

In the clinic when you have blood taken, the blood cells can be separated from the liquid part of blood – if you just put blood in a tube and wait, the red blood cells will settle to the bottom. How quickly red blood cells settle to the bottom of the tube can be measured, and is called the erythrocyte sedimentation rate, sed rate or ESR. Increased ESR can indicate inflammation related to cancer, infection or inflammatory disease. However ESR can also be elevated in some normal healthy individuals, so results must be considered in context.

How is my amount of red blood cells measured?

One way to quantify your red blood cells is to use a microscope to look at the cells in blood. We can count the number of red blood cells in a certain volume of blood to get a ‘red blood cell count’. We can also measure your ‘hematocrit’ or HCT, the percent of your blood that’s composed of red blood cells. Hematocrit is determined by separating the blood cells from the blood liquid, and comparing the sizes of those two fractions. The greater your hematocrit, the more of your blood is taken up by red blood cells.

What does it mean if I have anemia?

Anemia is defined as a decreased number of circulating red blood cells. Since red blood cells carry oxygen to tissues, and oxygen helps tissues to use fuels like sugar to generate energy, low levels of red blood cells can result in symptoms of low energy:  fatigue and weakness. Other symptoms of anemia are pallor, since red blood cells help give our skin colour, and shortness of breath, as the body tries to get more oxygen into itself.

How may the cause of anemia be determined?

One way to distinguish causes of anemia is to count cells called reticulocytes – reticulocytes are immature red blood cells that have just entered the bloodstream. Low levels of reticulocytes could suggest a decrease in the production of red blood cells, whereas high levels suggest the body is trying extra hard to produce red blood cells. Causes of anemia can also be distinguished by the size of the red blood cells – which are classified as microcytic (small), normocytic (normal) or macrocytic (large). Red blood cell size is reported as ‘mean cell volume’ or MCV. The red cell distribution width, or RDW, represents the degree of variability in red blood cell size – a small RDW means all red cells are very similar in size.

What does my hemoglobin (HGB) level mean?

Red blood cells are basically bags full of a protein called hemoglobin. Hemoglobin binds oxygen molecules – the more hemoglobin in a red blood cell, the more oxygen that cell can carry. You can think of red blood cells like delivery trucks, filled with hemoglobin boxes, with each hemoglobin box holding some oxygen atoms. If you don’t have enough hemoglobin, or your hemoglobin is defective, not as much oxygen can be carried by your red blood cells. This can lead to the same symptoms as anemia.

How are levels of white blood cells and platelets determined?

The amounts of white blood cells and platelets are typically assessed by counting how many white cells and platelets are in a certain volume of blood, under a microscope.

What does it mean if my platelet (PLT) count is outside the normal range?

Since platelets are involved in stopping bleeding, low levels of platelets can results in symptoms such as easy bruising, nosebleeds, heavy periods, or more bleeding after the dentist. High levels of platelets can cause excessive blood clotting. Note though, there are many other factors involved in stopping bleeding, so excessive bleeding or clotting isn’t necessarily a platelet problem.

What does it mean if my white blood cell (WBC) count is outside the normal range?

As white blood cells are involved in immune response, lower levels of white blood cells can increase susceptibility to infection. Higher levels of white blood cells can be a sign of an inflammatory process.

What is a white blood cell differential?

A count of how many there are of each white blood cell type in a certain volume of blood gives us a ‘white blood cell differential’, often called just ‘a differential’.  The types of white blood cells typically counted are neutrophils, eosinophils, basophils, monocytes and lymphocytes. Neutrophils are the most abundant, representing 60-70% of white blood cells in adults.  Identifying which types of white blood cells are most affected can help suggest why a white blood cell count is abnormal.

What do the different types of white blood cells do?

Generally, neutrophils are involved in defense against bacteria, eosinophils are involved in defense against parasites, basophils are involved in allergic responses, and monocytes can enter tissues and become macrophages, which consume cellular material. Lymphocytes include both B and T-cells; B-cells are involved in antibody production, and T-cells are involved in defense against viruses and cancer cells.

What are band neutrophils?

Band neutrophils are immature neutrophils. Increased band neutrophils may be a sign that the body is pumping out a lot of new neutrophils, and thus that immune system defenses have been stimulated.

What is blood plasma?

About half the volume of blood is a fluid called plasma. Plasma contains water plus dissolved molecules including proteins, hormones, antibodies, vitamins, minerals, electrolytes and carbon dioxide. Some of the proteins in plasma help blood to clot.

What is serum?

Serum is plasma that’s had a certain protein involved in blood clotting, called fibrinogen, removed.

What kinds of things may be measured in a blood chemistry test and why?

Levels of albumin, beta2-microglobulin, immunoglobulins such as IgM and IgG, and lactate dehydrogenase, can be measured in blood plasma to indicate disease severity. Albumin makes up about 60% of all plasma protein, and functions to keep the solute concentration of plasma high enough that enough water remains in blood vessels. Albumin is made in the liver before being released into the blood. The albumin in your blood is typically measured to suggest impacts of disease on the ability of the liver to function – the less well the liver can function, the less albumin may be present in the blood. Another plasma marker of disease severity, Lactate dehydrogenase (LDH), is involved in cell metabolism, and so is normally found inside cells, not free in the plasma. Elevated lactate dehydrogenase in the plasma can suggest that cells somewhere in the body are breaking open, which could be a result of many different disease processes.

 Normal values for blood cell counts can be found at:  http://www.llscanada.org/#/diseaseinformation/managingyourcancer/newlydiagnosed/understandingdiagnosis/labimagingtests/bloodtests/bloodcounts/


LeBlond RF, DeGowin RL, Brown DD. Chapter 18. Common Laboratory Tests. In: LeBlond RF, DeGowin RL, Brown DD, eds. DeGowin’s Diagnostic Examination. 9th ed. New York: McGraw-Hill; 2009. http://www.accessmedicine.com/content.aspx?aID=3658306. Accessed November 13, 2013.

Nicoll D, Lu CM, Pignone M, McPhee SJ. Chapter 8. Diagnostic Tests in Differential Diagnosis. In: Nicoll D, Lu CM, Pignone M, McPhee SJ, eds.Pocket Guide to Diagnostic Tests. 6th ed. New York: McGraw-Hill; 2012. http://www.accessmedicine.com/content.aspx?aID=56996835. Accessed November 13, 2013.


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