RELEVANCE OF ABSOLUTE VALUES IN CBC (COMPLETE BLOOD COUNT) TEST – (Basic Concept of Laboratory Diagnostics)

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RELEVANCE OF ABSOLUTE VALUES IN CBC (COMPLETE BLOOD COUNT) TEST – (Basic Concept of Laboratory Diagnostics)

Nitin Nayyar, Scientific Communications Coordinator, HORIBA Medical, New Delhi

In the niche of haematology, the cellular components of the blood are regularly measured. However, the use of absolute or relative values of number of blood cells remains questionable controversial and has received clashing opinions from many medical experts from various medical specialities. Many internists progressively pay attention to the absolute values in the complete cell count. Although, representatives of other specialties, such as paediatrics, do appreciate the relative values due to the larger persistence related to age dependency.

One of the most frequently applied laboratory methods is the differentiation of cellular components of white blood cells. However, since its introduction, manual differentiation has been subject to relatively little changes over the last many years. A differential blood count has to be performed to precisely assess an increased or reduced white blood cell (WBC) count.

A complete blood count (CBC) is a panel test that gives information about the cells in a patient’s blood.It is generally requested by a doctor or another medical practitioner to diagnose specific diseases and to confirm the health status of the patient.A study reveals that a great number of clinical decisions and diagnoses are supported by laboratory medicine and clinical information obtained from laboratory tests, which plays a vital role in the diagnosis of various pathologies. Some studies have shown that although physicians usually request laboratory tests, they tend to misinterpret or ignore the results; such unacceptable interpretations have obvious impact on the treatment and quality of patient care.

Illustrations: To highlight intrinsic role of absolute Values:

  1. In a patient with chronic myeloid leukemia, the increase in basophil concentration is a vital diagnostic criterion. A relative value of 1% basophils with an aggregate WBC count of 100,000 cells/μL may give off an impression of being normal, but when considering the absolute value, this shows pathological basophilia with a high count of 1,000 cells/μL.
  2. Normal values for total WBC and differentialin adult males and females are:
  • Total WBC: 4,500 – 10,000
  • Bands or stabs: 3 – 5 %
  • Agranulocytes
    • Lymphocytes: 25 – 35% relative value (1700-3500 absolute value)
    • Moncytes: 4 – 6% relative value (200-600 absolute value)
  • Granulocytes
    • Basophils: 0.4% – 1.1% relative value (40-110 absolute value)
    • Eosinophils: 1 – 3.1% relative value (100-310 absolute value)
    • Neutrophils : 50 – 70% relative value (2500-7000 absolute value)

To make a precise assessment, one should keep in account, both relative and absolute values. For example a relative value of 70% neutrophils may seem very normal; however, if the total WBC is 20,000, the absolute value (70% x 20,000) would be an abnormally high count of 14,000,which is alarming.

  1. Lymphocytes are the only exception as it can be divided into relative lymphocytes and absolute lymphocytes. Normally 20%–40% of human WBC are lymphocytes. When the percentage exceeds 40%, it is known as relative lymphocytes. When the total lymphocyte count in blood is more than 4000/μL in adults, 7000/μL in adolescents, and 9000/μL in infants, the patient is identified with absolute lymphocytosis.

How difficult it becomes to decide on the Relative value: Evidence through numbers

Cell TypeValue (%)Relative Value(cells)
Neutrophils60-703,000-7,000
Eosinophils1-450-400
Basophils0.5-1.025-100
Lymphocytes20-301,500-4000
Monocytes26100-500
ANC=1,500-2,000Not Significant
ANC=1000-1,500Minimal Risk
ANC=500-1000Moderate Risk
ANC=<500Severe Risk

Why do you need to consider absolute counts?

The reason to consider absolute counts is very vital because if you just have a look at percentages, you could not have a clear idea. Let’s say, there are 61% neutrophils in a particular patient. You might take a glimpse at that and think, okay, that lookspretty fine. But if you don’t take the time to know the absolute neutrophil number, you could be missing a very crucial thing. If the WBC count in a particular patient is very low than the demanded, say 1.5 (normal being 4-11), then the patient would certainly have a low number of neutrophils, nonetheless, the percentage of neutrophils lies in the normal category.

Contrarily, if the same patient has a very high WBC (assume 110), then 62% of the total WBC would be a very high number! So, by just looking at the percentage of neutrophils, you might go okay, that looks fine .But, if one consider closely, the number of neutrophils would be very high. So that’s the theory that goes in favor of the absolute numbers. In reality, most of the time you can just have a glimpse at the WBC, then further figure out the absolute numbers of the individual white cells.

Case Study: High lighting Relevance of Absolute numbers

A 57-year-old man with a fever and some other problems like fatigue.
The CBC shows a WBC of 2.0 × 109/L with the following differential:

  • Basophils 0% (0–2%)
  • Eosinophils 0% (0–7%)
  • Monocytes 10% (0–12%)
  • Lymphocytes 50% (15–45%)
  • Neutrophils 40% (40–70%)

Based on the results and its connected reference range, one might conclude the patient has lymphocytosis (albeit relative) and continue diagnostic considerations based on these findings. But, if these differential results are converted into absolute values, the following data can be more appropriately assessed:

  • Basophils 0.00 × 109/L (0.0–0.1 × 109/L)
  • Eosinophils 0.00 × 109/L (0.0–0.4 × 109/L)
  • Monocytes 0.20 × 109/L (0.2–0.8 × 109/L)
  • Lymphocytes 1.00 × 109/L (1.0–3.4 × 109/L)
  • Neutrophils 0.80 × 109/L (1.8–6.8 × 109/L)

Now we can easily conclude that the patient has moderate neutropenia and may be at risk of some infection. Besides, we now focus our diagnostic points on the causes of neutropenia. We also realize that the patient does not have a true lymphocytosis, as the absolute lymphocyte count is at the lower range.

Understanding Intrinsic nature of Absolute Values: Learning through Example

A progressive decline of T helper (CD4+) lymphocytes T shows the identification of the infection with the human immunodeficiency virus (HIV) . The main reason for this depletion occurs because the virus infects and kills CD4+ T lymphocytes, the main mechanism for programmed cell death apoptosis . These cells mainly act as regulators and amplifiers of the immune response and are related with the immunopathogenesis of HIV infection.

Thus, the decline of CD4+ T cells results in a weakened immune system which results in the progression of infection to AIDS(human immunodeficiency syndrome) and death due to conditions associated with the same infection.

The level of CD4+ T cells is consideredto be one of the most vital immunological parameters in HIV-infected individuals to evaluate their prognosis and precise results of immune deficiency, to decide the inception of antiretroviral therapy, to monitor the effectiveness of this treatment, to assess the need to start or discontinue prophylaxis, and to establish the diagnosis of AIDS.

Thus, quantification of CD4+ lymphocytes is a crucial procedure in the assessment of patients with HIV. Immunophenotyping provides significant information about the leukocytes of the whole immune system, differentiating the total lymphocytes (CD45+), T lymphocytes (CD3+), and subtypes of T lymphocytes which comprise two subsets: cytotoxic T cells (T lymphocytes CD3+/CD8+)  and helper T cells (T lymphocytes CD3+/CD4+). Thus, the total lymphocyte count and percentage values of lymphocyte subsets may be calculated by using CD45+ monoclonal antibody, using flow cytometry, in association with CD3+, CD4+, and CD8+ antibodies.

The absolute count of lymphocytes may be greatly influenced by biological factors that impact the total count of lymphocytes and leukocytes, such as the use of drugs that suppresses the bone marrow, acute infections (e.g., malaria, sepsis, and tuberculosis), and pregnancy, which may lead to hemodilution.Other than these biological factors, there could also be a variation because of the methodological factors such as differences in the methods.
Several studies have reported that variations in the percentage count of CD4+ T lymphocytes are not so stable parameters than variations in the absolute count to assess the progression of the disease.

The main concern regarding the use of counting the percentage of CD4+ T cells is how the variation of results could have a great impact on big decisions related to the care of people infected with HIV and the clinical treatment.

Understand in a simpler language, let’s go through the below explanation:Complete blood count (CBC)

Blood is made up of nutrients, water, proteins and living cells. A CBC tells about cancer care team about the cells in the blood. It quantifies3 basic types of blood cells:

  • Red blood cells
  • Platelets
  • White blood cells

Each of these cells has a unique and important purpose.

Red blood cells (RBCs)

RBCs carry oxygen to the cells and carbon dioxide away from the blood cellsin one’s body.

The CBC measures red blood cells in many ways, but the simplest measure is either

Hemoglobin (Hgb)
or
Hematocrit (Hct)

When the Hct values and Hgbfall too low, it’s called anemia.

Platelets (Plts)

Platelets help control bleeding. One may bleed easily when one’s platelet levels are low. The risk of bleeding goes up very high when platelet levels go below 20,000.

But, knowing the absolute values help doctors to a great extent to work in the right direction.So, the disease can be cured easily and promptly.

White blood cells (WBCs)

The most significant infection-fighting WBC is the neutrophil. The number of doctors look for the absolute neutrophil count . A healthy person has an ANC between 2,500 and 6,000.

But,let’s assume that a  person is having ANC of 5900. That doesn’t imply that person is completely healthy as it gives an indication to keep a check on the health of the person. So, it’s very much necessary to get the precise results, which one can get by knowing the absolute values.

The ANC is calculated by multiplying the WBC count with the percent of neutrophils in the blood. For instance, if the WBC count is 9,000 and 50% of the WBCs are neutrophils, the ANC is 4,500 (9,000 × 0.50 = 4,500).

When the ANC falls below 1,000 it is called neutropenia . Doctor will have to watch one’s ANC closely because the risk of infection is much higher when the ANC is below 500.But, the absolute values can vanish this drawback as it can be easily concluded from the reports that what actions have to be taken for the care of the patient.

Therefore, it may be concluded that absolute numbers are better indicators to diagnose, understand and treat precise disease and relative numbers do not give a clear idea about the patient’s actual pathology.

 

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