Haematology 101: Why a manual white blood cell count matters
We’ve all been there.
You’re running your haematology sample, looking down at your results and you’re thinking ‘yep, those are my white blood cells…’
And that’s the end of it.
But have you ever thought about why we see changes to our white blood cells, and what it all means for our patients?
The reality is that a lot of medical conditions cause changes to our leukogram (our WBC levels), and so as nurses, it’s really important that we understand the common changes we see, and why they happen!
And that’s what I’m going to talk you through in this post. By the end of it, you’ll know how to perform a differential white blood cell count, why leukocytosis and leukopenia occur, and how we can support patients with WBC disorders.
What is a leukogram?
The leukogram, or white blood cell differential, tells us about the levels of each individual white blood cell within the bloodstream.
This is done using either an automated analyser (as part of a routine haematology test) or manually, by looking at a blood smear.
Automated WBC differentials are recorded both as absolute cell counts (in cells/uL or x 10^9/L), and as percentages. Percentage counts can be misleading, especially in patients with very high or low WBC levels, and so an absolute cell count is preferred.
Depending on the haematology analyser you have in practice, your results may include a 3-part, 4-part, or 5-part differential cell count.
3-part differential: total granulocytes (neutrophil, eosinophil and basophil count combined), lymphocyte and monocyte counts
4-part differential: individual cell counts for neutrophils, eosinophils, lymphocytes and monocytes but not basophils
5-part differential: individual cell counts for all types of white blood cell.
A manual differential cell count is only able to give us estimated percentage counts of each cell type in practice.
Manual counts can be useful to confirm the results of an automated count. Our analyser counts can be incorrect as any large or nucleated cell may be counted as a WBC. For example:
Immature neutrophils may be mistaken for monocytes
Macroplatelets (large platelets) and immature red blood cells may be mistaken for WBCs
This means, ideally, you should always double-check your haematology analyser results with a blood smear!
How to perform a manual white blood cell count
1Examine the monolayer of the blood smear
Record the numbers of each type of white blood cell seen in each high power field
Continue counting and tallying until a total of 50 cells have been counted (across all WBC types)
Divide the number of neutrophils counted by 50, then multiply by 100
Divide the number of eosinophils counted by 50, then multiply by 100
Divide the number of basophils counted by 50, then multiply by 100
Divide the number of lymphocytes counted by 50, then multiply by 100
Divide the number of monocytes counted by 50, then multiply by 100
Neutrophilia and neutropenia
Neutrophils are the most common WBC in circulation.
These cells are produced in the bone marrow, where they mature through three different compartments, the:
Proliferation,
Maturation, and
Storage compartments
Before being released into the blood vessels. Within vessels, neutrophils either circulate in the bloodstream (in what we call the ‘circulating’ neutrophil pool) or adhere to vessel walls (in what is called the ‘marginal’ neutrophil pool).
Neutrophilia
Neutrophilia is an increase in neutrophil numbers and is the most common reason for an increased total WBC level.
A neutrophilia can either be:
Mature: where there is an increase in mature or developed neutrophils without an increase in immature or band neutrophils, or
With a Left-Shift: where lots of immature or band neutrophils are present alongside mature cells.
Neutrophilia can be caused by a number of different factors, which we classify as either physiological, stress or steroid-induced, or due to inflammation.
Physiological or adrenaline-induced causes include fear, excitement, exercise, hypertension, seizures and parturition
Stress or steroid-induced causes include pain, anaesthesia, trauma, neoplasia, hyperadrenocorticism, chronic disease and metabolic disease
Inflammatory causes include or infection, tissue trauma, tissue necrosis, immune-mediated disease, burns, neoplasia, haemorrhage, haemolysis, metabolic diseases and neutrophil function disorders.
Neutropenia
Neutropenia is a decrease in circulating neutrophils.
Several factors can cause neutropenia, and these are divided into three main categories:
Decreased production within the bone marrow
Sequestration of neutrophils in the marginal pool (where they stay adhered to vessel walls)
Excessive demand or consumption of neutrophils.
Causes of decreased production include drug-induced side effects, bone marrow disease, infectious diseases and toxin ingestion. Chemotherapy is a classic example of drug-induced neutropenia.
Sequestration is caused by anaesthesia, anaphylaxis and endotoxic shock.
Neutrophil consumption can be caused by severe, acute overwhelming infection, neoplasia and immune-mediated disease.
Patients with neutropenia are less able to deal with an infection, so we need to be very careful with how we nurse these patients:
Prophylactic antibiotics may be given to prevent infection
Hospitalisation for intravenous antibiotic administration and close monitoring may be needed in severe cases
Patients should be barrier nursed to protect them from developing a hospital-acquired infection
A medication called filgrastim may be given in some cases, to increase circulating neutrophil levels. This is a granulocyte-colony stimulating factor. It is administered as a subcutaneous injection given over concurrent days.
Eosinophilia and eosinopenia
Eosinophils are the second most common granulocyte within the circulation.
They are formed in the bone marrow and mature there before entering the circulation. They only stay in the circulation for a short period before they migrate into tissues.
As well as playing an important role in phagocytosing pathogens, eosinophils are also involved in allergic reactions and parasitic infections.
Fun fact – lots of eosinophils are present within the mucous membranes!
Eosinophilia
Eosinophilia is an increase in eosinophils.
This is most commonly caused by parasitic infections, inflammatory or allergic diseases of the gastrointestinal tract, respiratory tract, urogenital tract and skin.
Common eosinophil-associated conditions include:
Eosinophilic enteritis (a form of IBD where eosinophils infiltrate the cells)
Eosinophilic bronchopneumopathy (a respiratory disease seen in dogs, where eosinophils infiltrate the lungs and bronchi)
Eosinophilia can also be seen with some cancers, for example, lymphoma and mast cell tumours.
Eosinopenia
Eosinopenia is an absolute decrease in eosinophil levels. This can be challenging to confirm because many haematology analysers have a normal range which goes down to zero!
Most of the time, low eosinophil levels are because of stress or steroid administration.
In times of physiological stress, or when steroids are administered, we see classic changes to our WBC levels, known as a stress leukogram:
Stress leukogram = neutrophilia + monocytosis + lymphopenia + eosinopenia.
This can be remembered using the mnemonic ‘SMILED’:
Segmented (aka neutrophils) and monocytes are increased, lymphocytes and eosinophils are decreased.
Basophils and basophilia
Basophils are the least common circulating white blood cell. They have a similar function to mast cells and contain histamine.
Basophils play an important role in allergic reactions and chronic allergies.
Basophilia
Basophilia is an absolute increase in circulating basophils.
This is normally seen in combination with eosinophilia, since both of these cells are involved in responding to allergies.
The most common causes of basophilia include:
Heartworm (not seen frequently in the UK, but can be seen in travelling dogs)
Allergic respiratory diseases
Parasitic infections
Some cancers
Basopenia is not considered a relevant finding. Many healthy animals have no basophils within their bloodstream - and most haematology normal ranges go down to zero! Have you ever seen a basophil on a blood smear? I think I’ve only ever seen a few - DM me on Instagram and let me know!
Lymphocytosis and lymphopenia
Lymphocytes are the second most common WBC in the circulation.
There are two forms of lymphocyte within the body – B-lymphocytes and T-lymphocytes.
Only around 10% of lymphocytes are present in the circulation. The remaining 90% located within lymphatic tissue around the body. These can then re-enter the circulation through the thoracic duct.
Lymphocytosis
Lymphocytosis is an increase in lymphocyte numbers and is generally seen either due to physiologic causes, or age-related causes.
Stimulation from antigens can also cause lymphocytosis, e.g. in cases of chronic inflammation, or infectious disease. However, this is rare..
Physiologic lymphocytosis occurs due to an adrenaline response. It is particularly seen in cats. This can be caused by stress, fear, excitement or strenuous exercise.
Age-related lymphocytosis occurs in young animals under 6 months of age. Tese patients have a higher lymphocyte count than adults.
Lymphopenia
Lymphopenia, or low lymphocyte levels, is usually seen due to stress or steroid use, as part of the stress leukogram.
Other causes include:
Active infection
Loss of lymphocytes (e.g. in chylothorax patients, or those with Lymphangiectasia – a GI disease causing leaking of lymphatic fluid within damaged intestines)
Congenital immunodeficiencies.
Monocytes and monocytosis
Monocytes develop in the bone marrow and enter the circulation. They then migrate into tissues, where they are known as macrophages. Macrophages engulf and remove cellular debris and pathogens.
Monocytosis
Monocytosis is an increase in circulating monocytes and is seen due to two main causes.
The first is stress. Remember the stress leukogram – segmented + monocytes are increased!
This is a common cause of monocytosis, especially in dogs. Acute or chronic inflammatory or infectious diseases are another common cause of monocytosis.
Like basophils, monocytopenia has no clinical significance. This is because healthy patients can have no circulating monocytes, and our analyser reference ranges can go down to zero.
Nursing considerations for WBC disorders
When it comes to nursing the white blood cell disorder patients, we need to think about:
Evaluating blood smears and double-checking our haematology machine values
Protecting patients from infection where significant decreases in white blood cells are present
Minimising fear and stress in our patients, to prevent it interfering with haematology results
Treating the underlying cause of the disorder, so administering steroids, antibiotics, and other specific treatments depending on the underlying disease
Educating clients on the importance of parasite prevention
So there’s quite a bit to think about with our leukograms!
Are you currently doing differential white blood cell counts in practice? If not, why not grab the microscope and take a peek at some blood smears?
Practice, practice, practice looking at those cells and noticing the difference between each WBC. You can perform practice cell counts, and double-check yourself against your patient’s haematology results as a rough guide, too!
And if you want to go through this live, in a relaxing, informal environment, join me on July 18th for my haematology nursing workshop. Together we’ll look at blood smears, identify normal and abnormal cells, perform cell counts, plan nursing care, calculate and administer transfusions and much more!
Save your spot here and don’t forget to DM me on Instagram and let me know when you’ve got your seat!
References
Day, MJ and Kohn, B. 2012. BSAVA Manual of Canine and Feline Haematology and Transfusion Medicine. 2nd ed. Gloucester: BSAVA.
EClinPath, 2013. Individual WBC. Available from: http://eclinpath.com/hematology/leukogram-changes/leukocytes/
Merrill, L, 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.
Sirois, M. 2020. Laboratory Procedures for Veterinary Technicians. 7th edition. Missouri: Elsevier.
