abcofcbc

ABC of CBC

Dr. MuKeSh M. DeSaI. M.D.

HaEmAtOlOgY & ImMuNoLoGy CeLl

• • Consultant Hematologist & Oncologist & Immunologist

    • • Sir Harkisondas Nurrotamdas Hospital

      • Balbhai Nanavati Hospital

• • • Chief Division of Immunology

• • Prof of Pediatric Hematology & Oncology

  • Department of Pediatric Hematology Oncology

  • Bai Jerbai Wadia Hospital For Children; Mumbai.

  • E Mail: mmdesai007@gmail.com

Introduction to CBC:

• • A complete blood cell count (CBC) is one of the most common laboratory tests in clinical practice.

  • More than 10% to 20% of CBC is reported as abnormal.

  • Therefore, it is in every pediatrician’s interest to have some understanding of test basics

  • A Pediatrician or Physician should have a structured action plan for interpretation of abnormal CBC results.

  • Today, Modern instruments like the coulter counter can electronically count circulating blood cells like red blood cells (RBCs), white blood cells (WBCs), and platelets,

  • They also provide useful Indices which provide the basis of Classifying Anaemias and also help us in their differential diagnosis.

  • Newer Parameters like MPV (Mean Platelet Volume) help us differentate X linked Thrombocytopenia from AITP.

Principle of Coulter Counter:

• • It generates an electrical pulse when a blood cell passes through a small aperture surrounded by electrodes.

  • Each electrical pulse represents an individual cell, and the pulse height indicates the cell volume.

  • It can therefore register the total cell count as well estimate the average cell volume and the variation in cell size. E.g. It can measure RBC numbers, measure RBC volume i.e. the mean corpuscular volume (MCV) and the RBC distribution width (RDW), respectively.

  • They are also capable of measuring cell content of WBCs and provide automated differential count (ie, 5-part differential).

  • The granulocyte count is fairly accurate and it can also provide absolute values for all blood count i.e Absolute Neutrophil count (ANC), Absolute Lymphocyte count (ALC), Absolute Eosinophil count (AEC).

  • Hemoglobin and hematocrit are the other measured variables by the coulter.

  • From this one can calculate the MCH, MCHC

Limitations of coulter counter:

• • Standardization of Machine is necessary to ensure consistent results

  • When accepting the platelet count and the automated WBC differential count it is always necessary to cross check it by the human eye.

  • E.g: it is possible that the machine may show a platelet count and the Direct peripheral Smear show a Normal platelet count. This condition is known as Pseudothrombocytopenia.

  • This may occur because the anticoagulant EBTA may clump the platelets and hence the coulter would record a decreased platelet count. Thus every low platelet count must be cross checked by peripheral smear before an elaborate investigation for thrombocytopenia is undertaken.

Evaluation of a CBC Report:

• • When interpreting a CBC report a pediatrician will have to focus on the following variables:

    • • Hb:

        • • As a general indicator of anemia or polycythemia.

      • MCV:

        • • A key parameter for the classification of anemias

      • RDW: (RBC distribution width)

        • • A measure of Anisocytosis meaning variation of cell size (a relatively useful parameter in the differential diagnosis of anemia)

      • RBC count:

        • • An increased RBC count associated with anemia is characteristic of the thalassemia trait.

      • Platelet count:

        • • To detect either thrombocytopenia or thrombocythemia.

      • WBC count with differential:

        • • usually gives important clues for the diagnosis of infections, hematological disorders like acute leukemia as well as for the presence of leukopenia and neutropenia.

          • An abnormal WBC count, the pediatrician should immediately ask which WBC type is affected: neutrophils, lymphocytes, monocytes, eosinophils, or basophils as this may provide important clue to a child’s clinical condition and aetiology.

Normal Variables of CBC:

• • While interpreting a CBC a pediatrician must note the normal values of individual parameter for age as they vary with age.

  • This is very important as many gross errors are made when this is not done.

  • Many Pathologists have preprinted normal values for adult in their CBC report hence a pediatrician is well advised to have a normal values of CBC parameters in their clinic and refer to it frequently.

TABLE OF NORMAL VALUES IN CHILDREN

• • Finally, an “abnormal” CBC should be interpreted within the context of a child’s baseline value because up to 5% of the general population without disease may display laboratory values outside the statistically assigned “normal” reference range

  • Differences in the CBC based on race and sex should be considered when interpreting results. Hence it is very important to have normal values for Indian Children available.

  • As a generalization, RBC-associated parameters are lower and platelet counts are higher in women compared with men.

Evaluation of CBC in a Child with Anemia:

• • Important principles of interpretation of CBC in ANEMIA are outlined:

    • • Make sure anemia is present and that the seemingly low Hb is not just a normal variation of Hb for age.

  • Classify anemia on Basis of MCV

    • • Microcytic (MCV, <80 fL or normal for age)

      • Normocytic (MCV, 80-100 fL or normal for age)

      • Macrocytic (MCV, >100 fL or normal for age).

This will help narrows the differential diagnosis in each child with anemia

• • Peripheral Blood Smear evaluation during the initial evaluation of anemia is a great asset in all subtype of anemia.

    • • It helps substantially in the differential diagnosis and provides guidance for further testing.

      • It can help narrow down the investigations in a child and substantially economize the investigations.

• • Microcytic Anemia

    • • The differential diagnoses for microcytic anemia are:

        • • Iron deficiency anemia (IDA)

          • Anemia of chronic disease (ACD)

          • Thalassemia

          • Sideroblastic anemia

          • Pb poisoning

          • Cu poisoning

          • Zinc ingestion

• • The most common cause of the microcytic anemias is IDA,

  • Do a PS and it will give you an important clue

  • Serum ferritin may be done to confirm iron deficiency.

    • • A low serum ferritin level is diagnostic of IDA.

      • Diagnosis of IDA is unlikely in the presence of a persistently normal or elevated serum ferritin level.

  • If the serum ferritin level is normal,

  • One needs to R/o Thalassaemia Minor:

• • Approach to Differential Diagnosis of Microcytic Hypochromic anaemia

D/D of IDA vs Beta Thalassaemia Minor:

• • • Children with chronic microcytosis especially if they belong to a community in whom thalassaemia is more common for e.g. Lohana community;

    • a diagnosis of thalassemia should be considered, and Hb electrophoresis should be done

    • Also look at RBC count if RBC count is > 5.0 x 10 e 9 / L it favours possibility of Thalassaemia Minor

    • Various other computed parameters may help one suspect beta Thalassaemia Minor. One such useful parameter is if the MCV/RBC ratio is < 11 it favours possibility of beta Thalassaemia Minor.

    • RDW may also help differentiate IDA from Beta Thalassaemia Minor in IDA RDW is elevated while in beta thalassaemia minor RDW is within the normal range.

For interpretation of Hb electrophoresis you may require a Hematologist help.

• • Hgb electrophoresis results are normal in the α-thalassemia trait and abnormal in the β-thalassemia trait as well as in other thalassemic syndromes.

  • Concomitant IDA or Megaloblastic anemia may mask the typical abnormality seen in the β-thalassemia trait, which is an increase in Hgb A₂ (α₂δ₂) level from the normal value of 2% to a value of > 3.5%.

  • Acquired microcytic anemia that is not IDA suggest the possibility of Anemia of chronic disease i.e microcytic ACD.

  • A child with disseminated Koch or RA having mild microcytic anemia not responding to iron supplement therapy is a classical example of anemia of chronic disease.

  • These children would benefit from Erythropoietin therapy.

Table of Differential diagnosis of Microcytic hypochromic anemia:

• • Interpretation of Serum Iron Studies report in Microcytic Hypochromic anaemia

Macrocytic Anemia

Causes of Macrocytosis:

• • B12 and folate deficiency

  • Macrocytosis secondary to reticulocytosis

  • Drug induced

  • Constitutional Hypoplastic anemia

  • Myelodysplastic syndrome

  • Liver disease

  • Hypothyroidism

  • Hemolysis

• • B12 deficiency is common in Indian children especially strict vegetarian and they are very commonly associated with severe periungual pigmentation and knuckle pigmentation.

  • It is also important to remember that megaloblastic anemia is very often associated with pancytopenia and their LDH levels are markedly elevated.

  • Bone Marrow evaluation is very important in Macrocytic anemia as this would help rule out Myelodysplastic syndrome.

  • Other investigation which may help is

    • • Thyroid function test

      • Liver function test

      • Depending on clinical condition work up for hemolysis may be necessary.

Normocytic Anaemia:

• • Causes of Normocytic anemia:

    • • Dimorphic anaemia

      • Anaemia of Chronic Illness.

      • Haemolytic Anaemias.

      • Bleeding

      • Anaemia of ESRD (Renal Insufficiency)

• • A child with normocytic anemia exclude potentially treatable causes like nutritional anemia combined iron and B 12 deficiency, bleeding, anemia of renal insufficiency, and hemolysis.

  • Retic count high may provide clue for hemolysis and presence of Hemolysis

  • LDH elevated may help detect hemolysis

  • Elevated creatinine will confirm anemia of renal failure.

  • PBS may help diagnose sickle cell, dimorphic anemia.

  • The differential diagnosis of a normocytic anemia that is not linked to bleeding, nutrition, renal insufficiency, or hemolysis is either normocytic ACD or a primary bone marrow disorder.

Leucocyte Abnormalities:

§ Principles of interpretation of WBC abnormalities

§ Is the WBC count abnormal for age is the first consideration?

§ Which WBC is affected, neutrophil, Lymphocyte, Eosinophils, Monocytes or Basophils?

§ What is the absolute value of these cells? E.g absolute neutrophil count. Always interpret in terms of absolute values and not in term of percentage of cells.

§ Are these WBC normal in morphology or have abnormal morphology; look at the peripheral smear and rule out leukaemia and classify whether this is granulocytosis, monocytosis, and lymphocytosis.

§ What is their trend in the disease process?

Leucocytosis:

Causes of Neutrophilic leucocytosis

Pyogenic infections Drug induced e.g steroids In case of brisk bleeding Systemic onset JRA Periodic fever syndrome Stress Myeloid leukaemia Growth factor use like G CSF. Myeloproliferative disordersPeripheral smear evaluation will help rule out leukaemia and may pick up clues which may suggest infiltration of bone marrow like leukoerythroblastic response.

Important point to note is every leucocytosis does not mean pyogenic infection and there are noninfectious causes of neutrophilic leucocytosis.

Lymphocytosis:

Viral infections Infectious mononucleosis CMV infection Lymphoproliferative disorder Whooping cough KochAddison’s disease.

Lymphocytosis:

PBS should be seen to r/o Acute Lymphoblastic leukaemia

Presence of Atypical Reactive T-cell lymphocytosis suggest viral infection

If the clinical scenario is consistent with viral infection; after the patient recovers, the CBC and PBS should be repeated to see whether the abnormality has resolved.

Extreme Lymphocytosis can be seen with whooping cough and the patient may be often referred to you as a case of acute leukaemia. However peripheral smear show normal looking mature lymphocytes and not abnormal lymphoblast.

Monocytosis:

Enteric fever Koch Recovery from neutropenia Viral infections Primary hemopoietic disorders like JMMLMonocytosis:

Absolute monocytosis that is persistent should be considered a marker of a myeloproliferative disorder (eg, chronic myelomonocytic leukemia) until proved otherwise by bone marrow examination and cytogenetic studies.

A hematology consultation is advisable for further evaluation.

Eosinophilia:

Worms Allergic conditions Tropical eosinophilia Loffler pneumonia Drug induced hypersensitivity syndrome e.g. Carbamezapine Hypereosinophilic syndromes Addisonian crisis Hodgkin’s disease Chrug Strauss syndrome Poly arteritis nodosa Myeloproliferative disorders M4 with eosinophilia Eosinophilic fascittisFirstly exclude causes of “secondary” eosinophilia like parasite infestation, drugs, comorbid conditions such as asthma and other allergic conditions, vasculitides, lymphoma, and metastatic cancer.

Stool test for ova and parasites.

In suspected case of primary eosinophilia Bone Marrow is required

A trial of deworming and a course of hetrazan should be given to all and response followed by measuring the absolute eosinophil count and not by eosinophil percentage as emphasized.

Basophilia

Allergic conditions Myeloproliferative disordersIs extremely rare to see basophilic leukaemia.

This is just a short list and a detailed list can be found in text book.

LEUKOPENIA

Neutropenia

Neutropenia is a sinister problem and requires immediate evaluation

Neutropenia is severe if ANC, <0.5 × 10⁹/L because of the associated high risk of infection.

Causes of severe neutropenia are

Drug induced Post viral Hemophagocytic Syndromes Kostmann syndrome Cyclic neutropenia Leukaemia Aplastic Hypoplastic anemia Autoimmune neutropenia Felty’s Syndrome

Table of Drug commonly associated with Neutropenia.

Sarcoidosis Thymoma Critical illness in ICU Congenital primary Immunodeficiency Syndrome§ SCID

in infancy if a child has lymphopenia you must suspect Severe combined immunodeficiency and it is the easiest diagnosis to make if pediatricians pay attention to Absolute Lymphocyte Count in CBC report.

Like Neutropenia Lymphopenia should be paid attention to and should be routinely seen for when a pediatrician looks at the CBC parameters.