Labs • The Blood Project

The following is the complete blood count (CBC) on the day you see the patient:

WBC (10⁹/L)	Hb (g/dL)	Hct (%)	MCV (fL)	PLT (10⁹/L)
13.5	13.2	40.5	93	303

What’s what: WBC, white blood cell count; Hb, hemoglobin; MCV, mean cell volume; MCHC, mean cellular hemoglobin concentration; RDW-SD, red cell distribution width-standard deviation; platelets, PLT; Normal values: WBC 5-10 x 10⁹/L, RBC 4-6 x 10¹²/L, Hb 12-16 g/dL, Hct 35-47%, MCV 80-100 fL, MCHC 32-36 g/dL, RDW-SD < 45 fL, platelets (PLT) 150-450 x 10⁹/L

How would you describe the complete blood count?

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Leukocytosis

What is the definition of leukocytosis?

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White cell > 11 x 10⁹/L

Thus, the patient does indeed have leukocytosis.

What is the next test result to consider?

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White blood cell differential

How is a white blood cell differential performed (more than one answer may apply)?

a

Using an automated blood counter

b

Inspection of a reticulocyte stain

c

Manually counting of cells on a Giemsa-stained peripheral blood smear

d

Examination of a leukoctrit

Automated differential

White blood cell differential scattergram — **Automated differential.** Example of a white blood cell differential scattergram obtained with an ***automated counter***. The differently colored clusters indicate different cell populations. These raw data are not shared with the front-line clinician, but rather are used to calculate a numerical differential.

Manual differential

The complete blood count and white blood cell differential - ScienceDirect — **Manual differential.** In a manual differential, a stained blood smear is examined under a microscope and white blood cells are counted and classified based on their appearance. A manual differential is usually performed when the automated differential is flagged for review or when the healthcare provider requests it. Source.

The white cell differential was carried out in this patient using an automated counter. The results are the following:

What is more useful: the relative or the absolute counts?

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Absolute counts!

Elevated or decreased white cell subset counts are defined by absolute counts.

To drive this point home, consider the following 3 hypothetical individuals:

Patient	Total white cell count	% Neutrophils
1	5 x 10⁹/L	70
2	0.1 x 10⁹/L	99
3	100 x 10⁹/L	2

Which patient has neutropenia?

a

Patient 1

b

Patient 2

Yes! Despite the fact that neutrophils comprise 99% of the white blood cells.

c

Patient 3

This is a classic picture for chronic lymphocytic leukemia.

So, we need to rely on absolute counts to define lower- or higher-than-normal values. Before interpreting a patient’s white cell differential. it helps to consult a “cheat sheet” of thresholds:

White cell subset	Cytosis (increased)	Cytopenia (decreased)
Total white cells	>11 x 10⁹/L	<4.4 x 10⁹/L
Neutrophils	>7.7 x 10⁹/L	<1.5 x 10⁹/L
Lymphocytes	>3.5 x 10⁹/L	<1.5 x 10⁹/L
Monocytes	>0.8 x 10⁹/L	<0.2 x 10⁹/L
Eosinophils	>0.35 x 10⁹/L	<0.04 x 10⁹/L
Basophils	>0.1 x 10⁹/L	<0.01 x 10⁹/L

So, we need to rely on absolute counts to define lower- or higher-than-normal values. Before interpreting a patient’s white cell differential. it helps to consult a “cheat sheet” of thresholds:

White cell subset	Cytosis (increased)	Cytopenia (decreased)
Total white cells	>11 x 10⁹/L	<4.4 x 10⁹/L
Neutrophils	>7.7 x 10⁹/L	<1.5 x 10⁹/L
Lymphocytes	>3.5 x 10⁹/L	<1.5 x 10⁹/L
Monocytes	>0.8 x 10⁹/L	<0.2 x 10⁹/L
Eosinophils	>0.35 x 10⁹/L	<0.04 x 10⁹/L
Basophils	>0.1 x 10⁹/L	<0.01 x 10⁹/L

The patient’s only absolute count that is out of range is the absolute neutrophil count (10.34 x 10⁹/L).

Therefore, she has neutrophilia.

What is included in the neutrophil count (more than one answer may apply)?

a

Promyelocyte

b

Myelocyte

c

Metamyelocyte

d

Band

e

Segmented neutrophil

A peripheral smear was examined, and was determined to be normal.

We can conclude that the patient has leukocytosis, owing specifically to neutrophilia.

Broadly speaking, neutrophilia can be separated into primary (clonal) and reactive causes. Clonal means that there is autonomous proliferation of neutrophils. Reactive indicates that the cause is coming from a source outside the neutrophil.

An otherwise healthy 47 year-old woman with chronic, incidentally discovered, mild neutrophilia is almost certainly going to have a reactive cause. Let’s consider the possibilities in table format:

Cause	Patient History
Infection	Negative history
Inflammation	Negative history of rheumatological disorder, inflammatory bowel disease
Smoking	2 packs per day
Metabolic syndrome	Not obese, no diabetes
Cushing’s disease	No evidence on history or physical exam
Solid tumor	Asymptomatic, up to date on cancer screening
Medication	Not taking steroids, lithium or beta agonists
Stress	Denies emotional stress or extreme exercise
Splenectomy	Negative history

A C-reactive protein was ordered to screen for inflammation, and this was normal.

Based on these considerations, smoking is the likely cause of the patient’s neutrophilia.

Is it possible to have neutrophilia with a normal white cell count?

a

Yes

b

No

Here is an example from a different patient:

The numbers on the left of the differential are expressed as a % of the total white cell count. Those on right, indicated by “Abs” are absolute counts expressed as 10⁹/L. Im gran, immature granulocytes, includes metamyelocytes, myelocytes, and promyelocytes.

The learning point here is that a normal count can belie abnormalities in the differential, and we won’t know about these unless we look!