INTRODUCTION
The subject of Hematology (the Greek word “haima” meaning “blood”) has grown by leaps and bounds ever since the invention of the microscope. Hematology is a unique super-specialty in Medicine that encompasses the fields of Pathology, Physiology, Molecular Biology, Biochemistry, Obstetrics and Gynecology, Medicine, and Pediatrics.
The era of diagnosis has changed from simple microscopy and manual methodologies to complex automated counters, application of cytogenetics, flow cytometry, and molecular technology.
The basic test performed on the peripheral blood – “Complete Blood Count” (CBC) is one of the most informative single investigations, expressing the health and disease status of the body, in the whole menu of laboratory medicine. A long journey is travelled by this single investigation from the era of only hematocrit/hemoglobin as a diagnostic tool to the most sophisticated multi-parts multi-parameters automation.
Automation, because of its accuracy, has changed the principles and methodologies, approaches, and conclusions of various disciplines of medicine. Few branches are modified to the extent that their entire philosophy is so much reoriented that it needs to be rewritten and hematology is one of them. Although the fact remains that, automation is no replacement for the study of a peripheral smear, it just compliments manual microscopy, just like ECG and X-ray chest compliments manual auscultation in clinical medicine.
Over the past 5 decades, hematology analyzers have evolved from semiautomated to fully automated ones. Many additional parameters have become available now. From the earlier instruments that used electrical impedance as the sole counting principle for blood cells, modern-day analyzers, also, use conductivity differences, cytochemical staining, light scatter, and flow cytometric principles. While enhancing the speed, accuracy, and precision of test results, these have also added a new dimension to hematology reporting. However, even in the wake of much technological advancement, the attention to numerical data with regards to the interpretation of test results has not changed.
As the automated analyzers become more advanced, their precision has shown enormous improvement and manual blood smear review rates have been on a steady decline. Still, many hematologists and trainee residents in laboratories have been performing a validation function rather than an interpretative one. An experienced reviewer can weigh the relative significance of observed findings and assess their importance within the context of other clinical data. A trained eye will also appreciate other morphological abnormalities that may be undetected by automated review.
Hematology analyzers are marketed by multiple instrument manufacturers with varying levels of sophistication and technical complexity. These analyzers are equipped to produce, not only the traditional RBC, WBC, Platelet parameters but also many research and clinically important reportable parameters, along with three part, five-part, or six-part differential leukocyte count in less than one minute with a micro-volume of whole blood. Leucocyte positional parameters, which may diagnose specific diseases (e.g. differentiate between abnormal lymphocytes in leukemia and viral conditions and may also detect malarial infection) are now available.
Automated analyzer principles of operation, vary technologically. Electronic impedance and optical scatter are used by most of the analyzers. Sometimes Radiofrequency (RF) is used in conjunction with other methods. RF signals are proportionate to cell interior density or conductivity. Impedance and conductivity plotted against two-dimensional distribution cytogram or scatterplot, to evaluate cell populations with cluster analysis technology.
Flow cytometers with optical scatter system detect interference in a laser beam or light source to differentiate and evaluate cell types. The use of peroxidase (PEROX) and basophil - lobularity (BASO) channels, further improvises the generated results. Most of the sophisticated cell counters perform reticulocyte analysis using either fluorescent or other dyes. Limitations of the instruments result in specific flagging, which warrants evaluation with an alternative methodology.
There is a need for hematologists to give more clinically useful diagnostic opinions and further evaluation guidelines on blood samples run on automated analyzers instead of signing out a parameter-littered automated report printout.2
In automation generated CBC reports, graphical representation of results in the form of histograms or scatter plots, red cell distribution width (RDW), hemoglobin distribution width (HDW), and reticulocyte hemoglobin, immature platelet fraction, etc., have been largely ignored in favor of traditional numerical parameters over the years. These CBC parameters are very important as they provide useful information for the precise diagnosis and management of the patient.
What is CBC?
A complete blood count (CBC) is a series of tests used to evaluate the composition and concentration of the various cellular components of blood. It consists of the following tests:
- Red blood cell (RBC) count, white blood cell (WBC) count, and platelet count.
- Measurement of hemoglobin and calculation of hematocrit and red blood cell indices.
- White blood cells (WBC) total and differential count.
- Platelet count, mean platelet volume, plateletcrit, PDW, etc.
- Histograms, cytograms, scatterplots of RBC, WBC and platelets, etc.
Why CBC?
CBC is a comparatively inexpensive but powerful diagnostic tool in a variety of hematological and non-hematological conditions. It provides a myriad of valuable information about blood and to some extent the bone marrow, and also some direct or indirect shreds of evidence of health and disease status of various systems of the body. CBC is a window into the functional status of the bone marrow, the factory producing all blood elements. It is easily obtained, easily performed, relatively cheap, and serial measurements can evaluate response to therapy. The CBC may be used as informative tool for various sets of situations like:
- Diagnosis of anemia (Etiological and morphological types)
- Hemoglobinopathies (Thalassemia, sickle cell anemia, and hemolytic anemia)
- Bone marrow aplasia (Single lineage and multilineage)
- Nutritional deficiencies (Iron, vitamin B12, folic acid)
- Parasitemia (Malaria, filaria, leishmania)
- Thrombocytopenia [Primary (due to nonproduction), secondary (due to peripheral destruction) and bleeding disorders]
- Various viral fevers, and autoimmune conditions
- To diagnose infections, leukocytosis, leukopenia, eosinophilia, monocytosis, lymphocytosis, etc.
- Various hematopoietic malignancies like leukemias, various dysplasias like myelodysplastic syndrome, spillage of lymphoproliferative solid tumors, metastatic malignancies
- To diagnose the effect of various drugs including chemotherapy and radiation therapy and effects of various toxins and chemicals
- To diagnose effect of various types of stresses like traumatic, metabolic, neoplastic, and surgical stresses.
To conclude, it may be emphasized that not all hematological and nonhematological disorders can be diagnosed after an automated analysis of CBC but some direct or indirect, indicative, or diagnostic feature may be picked up by the instrument or on a peripheral smear. Along with numerical data, the histograms and scattergrams from automated hematology analyzers provide valuable information regarding common hematological conditions. It is important that operators and the end-users must have a basic understanding of the graphical output while interpreting their numerical data. This can enhance the diagnostic utility of automated data, ultimately benefiting the patient with better diagnosis and outcome.
Various Parameters of CBC
About 33 parameters can be obtained by most sophisticated counters (observed and calculated), which include:
RBC parameters | WBC parameters | Platelet parameters |
---|---|---|
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|
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(# = absolute count, % = percent count) |
Normal Values of Various Parameters of CBC
CBC values vary by age, sex, race, and demography. Normal values (reference range) are ultimately determined by the laboratory performing the test in the particular population. As a guide, the normal values for men and women are as follows:
Various Indices by Age Group and Conditions
Newborn |
Normal range | SI unit | |
---|---|---|
Hematocrit | 42–68% | 0.42–0.68% |
Hemoglobin | 15.4–24.5 g/dL | 9.6–15.3 mmol/L |
RBC count | 4.1–6.2 million/µL | 4.1–6.2 × 1012/L |
MCV | 103–106 µ3 | 103–106 fL |
MCH | 36–38 pg | 2.24–2.37 fmol |
MCHC | 34–36 % | 21.10–22.34 mmol/L |
Platelets | 100000–300000/µL or mm3 | 100–300 × 109/L |
Up to one year of age |
Normal range | SI unit | |
---|---|---|
Hematocrit | 29–41% | 0.29–0.42% |
Hemoglobin | 9.0–14.5 g/dL | 5.6–9.1 mmol/L |
RBC count | 3.6–5.5 million/µL | 3.6–5.5 1012/L |
MCV | 78 µ3 | 78 fL |
MCH | 25 pg | 1.55 fmol |
MCHC | 32% | 19.86 mmol/L |
Pregnancy |
Normal range | SI unit | |
Hematocrit | ||
Trimester 1 | 35–46 % | 0.35–0.46% |
Trimester 2 | 30–42 % | 0.30–0.42% |
Trimester 3 | 34–44 % | 0.34–0.44% |
RBC count | ||
Trimester 1 | 4.0–5.0 million/µL | 4.0–5.0 × 1012/L |
Trimester 2 | 3.2–4.5 million/µL | 3.2–4.5 × 1012/L |
Trimester 3 | 3.0–4.9 million/µL | 3.0–4.9 × 1012/L |