Lecture on RBC Indices and Anemias

CASE STUDIES

CASE 1

  • Patient Information: 25-year-old patient with a history of fatigue.
    • Lab Results:
    • RBC: 3.7 x 10^6/µl
    • Hb: 8.0 g/dl
    • MCV: 62 fl
    • MCH: 19.0 pg
    • MCHC: 27 g/dl
    • WBC: 5.3 x 10^9/l
    • Platelets: 400 x 10^9/l
  • Impression: Microcytic hypochromic anemia.

CASE 2

  • Patient Information: 30-year-old male patient with fatigue.
    • Lab Results:
    • RBC: 4.5 x 10^6/µl
    • Hb: 11.0 g/dl
    • MCV: 115 fl
    • MCH: 25.0 pg
    • MCHC: 30 g/dl
    • WBC: 7 x 10^9/L
    • Platelets: 350 x 10^9/L
  • Impression: Macrocytic anemia.

CASE 3

  • Patient Information: 23-year-old male patient.
    • Lab Results:
    • RBC: 4.5 x 10^6/µl
    • Hb: 11.0 g/dl
    • MCV: 87 fl
    • MCH: 30.0 pg
    • MCHC: 33 g/dl
    • WBC: 6.5 x 10^9/L
    • Platelets: 350 x 10^9/L
  • Impression: Normocytic normochromic anemia.

DR. MANAN SHAH - POST GRADUATE MD PATHOLOGY

DIAGNOSTIC UTILITY OF RBC INDICES

OBJECTIVES

  • To define and calculate the RBC Indices.
  • To describe the application of RBC indices in diagnosing various disorders.
  • To interpret RBC Histograms.

RBC INDEX

  • Definition: RBC index is a quantitative measurement of red blood cells, amount, and concentration of hemoglobin in them.
  • Historical background: Introduced by Wintrobe in 1929 to define the size (MCV) and hemoglobin content (MCH & MCHC) of red blood cells.

DEFINITIONS

  • Mean Cell Volume (MCV): Measure of average volume of RBCs.
  • Mean Cell Hemoglobin (MCH): Measurement of the average weight of hemoglobin in individual erythrocytes.
  • Mean Cell Hemoglobin Concentration (MCHC): Average concentration of hemoglobin in erythrocytes, expressed as g/dl.
  • Red Cell Distribution Width (RDW): Measure of variability of erythrocyte size.

REASONS FOR RBC INDICES

  • Used to classify erythrocytes by their volume and hemoglobin content.
  • Helps in providing significant information on the appearance of RBCs microscopically, especially for anemia diagnosis.
  • Laboratory professionals correlate the indices with hematocrit (Hct), Hemoglobin (Hb), and RBC count to identify technical issues when they occur.

MEAN CELL VOLUME (MCV)

  • Calculation Formula:
    MCV = \frac{Hct (L/L) \times 1000}{RBC count (x 10^{12}/L)}
  • Classification:
    • Normocytic: 80-100 fl
    • Microcytic: Red cells with reduced volume (<80 fl)
    • Macrocytic: Red cells with increased volume (>100 fl)
  • Note: MCV measures volume; estimation of size of flattened cells measures cell diameter, which are not the same.

MEAN CELL HEMOGLOBIN CONCENTRATION (MCHC)

  • Definition: Average concentration of hemoglobin in a deciliter of erythrocytes.
  • Calculation Formula:
    MCHC = \frac{Hb (g/dl) \times 100}{Hct (L/L)}
  • Classification:
    • Normochromic: 32-36 g/dl
    • Hypochromic: <32 g/dl
    • Hyperchromic: >36 g/dl
  • Hypochromic Definition: If the central pallor is >1/3rd of the cell size.
  • Hyperchromic Definition: Only the erythrocyte hyperchromic with an MCHC > 36 g/dl is the spherocyte.
  • Apparent hyperchromasia is usually due to artifactual increase from hemolysis, lipemia, or large numbers of Heinz bodies.

MEAN CELL HEMOGLOBIN (MCH)

  • Definition: Average weight of hemoglobin (in picograms, 10^-12 g) in individual erythrocytes.
  • Calculation Formula:
    MCH = \frac{Hb (g/dl) \times 10}{RBC (x 10^{12}/L)}
  • Normal range: 28 to 34 pg.
  • Relationship: MCH varies in direct linear relationship with MCV.
  • Cells with reduced volume contain less Hb, and vice versa.

MCH CHANGES

  • Increase in MCH: Possible causes include:
    • B12 deficiency
    • Folic acid deficiency
    • Reticulocyte response
    • Hemolytic anemia
    • Alcoholism
  • Decrease in MCH: Possible causes include:
    • Iron deficiency anemia
    • Thalassemia
    • Anemia of chronic disorders.

CASE 4

  • Patient Information: 25-year-old patient with fatigue.
    • Lab Results:
    • RBC: 3.0 x 10^6 /µl
    • Hb: 8.0 g/dl
    • MCV: 62 fl
    • MCH: 19.0 pg
    • MCHC: 30 g/dl
    • WBC: 5.3 x 10^9/l
    • Platelets: 400 x 10^9/l
  • Impression: Microcytic hypochromic anemia.
  • Differential Diagnosis: Not provided.

RED CELL DISTRIBUTION WIDTH (RDW)

  • Purpose: RDW helps describe RBC population size variations better than MCV alone when significant variation occurs.
  • Coefficient of Variation Formula:
    RDW = \frac{Standard \ deviation \ of \ MCV \times 100}{MCV}
  • Normal Value: 11.5-14.5%
  • Increased RDW: Indicates anisocytosis.

RDW AND MCV

  • Differential Diagnosis Based on RDW and MCV:
    • Normal RDW: Thalassemia carrier, Chronic disease anemia.
    • Low MCV and RDW: Iron deficiency anemia, Sickle-cell anemia.
    • High MCV and High RDW: Megaloblastic anemia, immune hemolytic anemia.
    • Normal MCV and Normal RDW: Sickle-cell trait, hereditary spherocytosis diagnosis.

FURTHER EVALUATION

  • For Iron Deficiency Anemia (IDA):
    • Low serum ferritin levels
    • Increased Total Iron Binding Capacity (TIBC)
    • Decreased transferrin saturation
    • Peripheral blood smear: Pencil cells, anisocytosis.
  • For Thalassemia:
    • Peripheral blood smear: Target cells, basophilic stippling
    • RBC count: Normal/Raised
    • HbA2 levels >3.5%
  • For Sideroblastic Anemia:
    • Increased serum iron
    • Increased serum ferritin
    • Dimorphic anemia and Pappenheimer bodies observed.

CASE 5

  • Patient Information: 26-year-old patient with weakness, chronic PPI abuse.
    • Lab Results:
    • RBC: 3.0 x 10^6 /µl
    • Hb: 11.0 g/dl
    • MCV: 75 fl
    • MCH: 24.0 pg
    • MCHC: 29 g/dl
    • RDW: 17%
  • Impression: Microcytic hypochromic anemia.
  • Possible Vitamin B12 deficiency: Discussion on combined anemia and MCV evaluation.

Combined Deficiency Anemia

  • Overview: Macrocytosis absence in cobalamin/folate deficiency; clinicians should recognize overlapping deficiencies.
  • Objective: Develop predictive models differentiating IDA from combined deficiency.

CASE 6

  • Patient Information: 32-year-old with GI bleed and hemorrhoids.
    • Lab Results:
    • RBC: 3.0 x 10^6 /µl
    • Hb: 11.0 g/dl
    • MCV: 102 fl
    • MCH: 26.0 pg
    • MCHC: 32 g/dl
  • Impression: Macrocytic normochromic anemia.

RETICULOCYTES

  • Definition: Premature RBCs which contain remnants of ribosomal RNA.
  • Role: Indicates erythropoietic activity accurately in a blood smear.
  • Importance: Useful in monitoring response to iron therapy.

RETICULOCYTE COUNT METHODS

Manual Method

  • Romanowsky stain does not visualize reticulocytes effectively.
  • Supravital stains (e.g., New Methylene Blue) are used for clear visual identification.

Automated Method

  • Fluorescent flow cytometry enhances precision in counting reticulocytes.

CORRECTED RETICULOCYTE COUNT

  • Formula:
    Corrected \ retic \ count = \frac{Patient \ hemocrat}{Normal \ hematocrit} \times \% \ reticulocyte
  • Utility: Assesses erythropoietic degree in anemic patients.

STRESS RETICULOCYTES/ERYTHROPOIESIS

  • Explanation: Increase in reticulocytes in severe anemia or when the body requires more RBCs. Similar concept to