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 superspecialty in Medicine which encompasses the fields of Pathology, Physiology, Molecular Biology, Biochemistry, Obstetrics and Gynecology, Medicine and Pediatrics.
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 diagnostic tool to the most sophisticated multiparts multiparameters automation.
Automation, because of its accuracy, has changed 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 peripheral smear it just compliments manual microscopy just like ECG and X-ray chest compliment 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, in addition, use conductivity differences, cytochemical staining, light scatter, and flow cytometric principles. While enhancing the speed, accuracy, and precision of test results, this has 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.
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 printouts.
2In 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, 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 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 the blood and to some extent the bone marrow, and also some direct or indirect evidences 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:
- To diagnose 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)
- Parasitemias (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, leukopenias, eosinophilia, monocytosis, lymphocytosis, etc.
- Various hematopoietic malignancies like leukemias, various dysplasias like myelodysplastic syndrome, spillage of lymphoproliferative solid tumors, metastatic malignancies
- To diagnose effects 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 scatter grams from automated hematology analyzers provide valuable information regarding common hematological conditions. It is important that operators and the end users should 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:
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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
Hematocrit Hemoglobin RBC count MCV MCH MCHC Platelets | Newborn Normal range 42–68 % 15.4–24.5 g/dL 4.1–6.2 million/µL 103–106 µ3 36–38 pg 34–36 % 100000–300000/µL or mm3 | SI unit 0.42–0.68 L/L 9.6–15.3 mmol/L 4.1–6.2 × 1012/L 103–106 fL 2.24–2.37 fmol 21.10–22.34 mmol/L 100–300 × 109/L |
Hematocrit Hemoglobin RBC count MCV MCH MCHC | Up to One Year of Age Normal range 29–41 % 9.0–14.5 g/dL 3.6–5.5 million/µL 78 µ3 25 pg 32% | SI unit 0.29–0.42 L/L 5.6–9.1 mmol/L 3.6–5.5 1012/L 78 fL 1.55 fmol 19.86 mmol/L |
Hematocrit Trimester 1 Trimester 2 Trimester 3 RBC count Trimester 1 Trimester 2 Trimester 3 | Pregnancy Normal range 35–46 % 30–42 % 34–44 % 4.0–5.0 million/µL 3.2–4.5 million/µL 3.0–4.9 million/µL | SI unit 0.35–0.46 L/L 0.30–0.42 L/L 0.34–0.44 L/L 4.0–5.0 × 1012/L 3.2–4.5 × 1012/L 3.0–4.9 × 1012/L |