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The CBC in Pediatrics: A closer look. David Hilmers March 19, 2007. Objectives. How do we get a CBC? What are the artifacts that can cause erroneous values? What do the indices mean? What information can we obtain from CBC beyond HgB and Hct? Some example cases. Coulter Counter.

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The cbc in pediatrics a closer look l.jpg

The CBC in Pediatrics: A closer look

David Hilmers

March 19, 2007


Objectives l.jpg
Objectives

  • How do we get a CBC?

  • What are the artifacts that can cause erroneous values?

  • What do the indices mean?

  • What information can we obtain from CBC beyond HgB and Hct?

  • Some example cases.



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How does a Coulter Counter Work?

  • Blood is suspended in a weak electrolyte solution

  • Drawn through a narrow aperture separating two electrodes through which electric current flows

  • Voltage between electrodes creates “sensing field”

  • As particles pass through the field they increase the impedance between electrodes

  • Change in impedance is recorded

  • Change in impedance is directly proportional to volume of particle (MCV)

  • Analyze distribution of particles to get a size distribution (RDW)

  • Can distinguish platelets, RBC’s, WBC’s, reticulocytes

  • Measures hemoglobin (by optical densitometry), RBC count, MCV, RDW, all else is calculated


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Other Indices

  • Hct = MCV x RBC

    • Actually, of little value

  • MCH = Hgb / RBC

    • Gives idea whether cells are hypochromic

  • MCHC = Hgb / Hct or Hgb / (MCV x RBC)

    • Gives idea of surface area per unit volume of RBC’s


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Artifacts in Electronic Cell counting

  • Cold aggluntinins (such as from Mycoplasma)

    • Decrease RBC count, increase MCV, MCH

  • Hyperglycemia causes cells to swell

    • Increases MCV and hematocrit and decreases MCHC

  • Hypernatremia also causes cells to swell

    • Increases MCV and hematocrit and decreases MCHC

  • Leukocytosis causes counts to increase and increases the average size of cells

    • Increases hemoglobin, hematocrit, RBC, and MCV

  • Triglyceridemia causes increased hemoglobin reading

    • Increases hemoglobin, MCH, MCHC



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Case #1

  • Newborn infant (term twin B) with the following indices

    • Hgb 10.2

    • Hct 33.2

    • MCV 94.8

    • RDW 14.0

    • RBC 3.5 M

      Could this be iron deficiency anemia? Why or why not?


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Iron deficiency in newborn

  • Most likely due to blood loss, such as twin-twin transfusion

  • Newborn infants will take all the iron that they need from mother even if mother is iron deficient

  • Average amount of iron in body at birth is 250 mg (80 ppm)

  • At 6 months iron concentration will decrease to 60 ppm and infant becomes at risk for iron deficiency, especially if not taking iron-enriched foods or formula

  • Remember to supplement exclusively breast-fed babies at six months with iron


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Impact of iron deficiency anemia on mental development

  • In one study, infants with Hgb < 9.5 at 8 mos had decreased locomotor and hand-eye coordination

  • Infants with low ferritin levels, later had decreased language ability, and a 3.3 times increase in the odds of having an IQ < 70 by age 5


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Case # 2

  • You are given the following CBC from a newborn African-American male infant:

    • Hb 14.9

    • MCV 93

    • MCH 31

    • MCHC 33

    • RDW 14

    • RBC 5.7

    • Retic 4

    • Platelets 220

    • Spleen 1 cm

    • T bili 8.9, day 3

  • What is your diagnosis, if any?


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Alpha thalassemia

  • Predominant hemoglobin at birth is hemoglobin F composed of alpha and gamma chains

  • Hemoglobin A consisting of alpha and beta chains is not predominant until 6 months of life

  • Iron deficiency is not present at birth

  • Therefore, low MCV (<98) at birth is almost always due to alpha thalassemia

  • In African Americans is almost always benign, consisting of single gene deletion (1 of 4)

  • In Asians, however, may be more serious with multiple gene deletions. Should be investigated.

  • May be only opportunity to easily detect alpha thalassemia since after 6 months, can only detect beta thalassemia on HgB electrophoresis (elevated hemoglobin A2). Would need to do genetic studies to discover alpha thal.


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What is a low MCV?

  • By age 1 lower limit of normal

  • MCV = Age (yrs) + 70


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Case #3

  • Newborn Caucasian baby boy, born via C-section

    • HgB 17

    • MCV 107

    • MCH 32

    • MCHC 33

    • RDW 14

    • RBC 5.3

    • Retic 4

    • Platelets 220

    • Spleen not palpable

    • Infant pale HR 200, weak pulses


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Blood loss

  • Baby had bled out during delivery

  • Not hemodiluted yet

  • Needs circulatory support


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Case #4

9 month old Caucasian boy.

Hb 9.7

MCV 76

MCH 33

MCHC 38

RDW 18

RBC 4.7

Retic 8%

Platelets 340

Spleen 1 cm palpable

Bilirubin 18.7 on day of life 3

What is going on?


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Hereditary Spherocytosis

  • Caused by loss of spectrin and/or ankyrin giving cytoskeletal instability and surface area loss

  • Best test is osmotic fragility test

  • When MCHC is high, gives perspective on surface area to volume of cells. Highest when spheres present.

  • Other possible diagnostic use of MCHC is with autoimmune hemolytic anemia which causes the generation of microspherocytes


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Case #5

  • 18 month old Caucasian male with Tetralogy of Fallot

    • Hb 17.2

    • MCV 66

    • MCH 30

    • MCHC 32

    • RDW 17

    • RBC 5.8

    • Retic 1.7

    • Platelets 110

    • Spleen palpable 2 cm

  • What is the diagnosis and what does this child need?


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Fe deficiency in patients with polycythemia

  • Needs iron or will stroke out!!!

  • Iron deficiency state gives higher viscosity

  • Combination of polycythemia and iron deficiency can cause stroke


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Case #6

  • You are following a 16 year old male who is a top-notch cross-country runner, who has been feeling tired and not up to par this year

  • His indices are:

    • Hgb = 11.7

    • Hct = 35%

    • MCV = 80

    • MCH = 28.9

    • RDW = 16

  • What is your diagnosis and why?


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Jogger’s anemia and anemia of highly-trained athletes

  • Boyadijev N. et al: Br J Sports Med 34:200-204, 2000.

  • Compared indices of highly trained pubescent athletes with controls

  • Athletes had lower HgB, RBC count, and MCV than controls

  • Additionally, there is a phenomenom called “runner’s anemia” with blood loss from continued microtrauma, usually asx, but may have increased fatigue

    • Get plasma expansion with running and hemolysis from pounding of feet on pavement and hemoglobinuria

    • Should be considered when mild anemia is well-tolerated by an avid runner but may be symptomatic


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Use of MCV and RDW

  • MCV ↓ RDW ↑

    • Fe deficiency

    • PPV = 97.8%

    • Best test for IDA is CHr (concentration of HgB in reticulocytes), not yet generally available but coming soon

    • Trial of iron can be used as diagnostic tool with 2-3 mg/kg/d of elemental iron (FeSO4 is 20% elemental)

    • Should see retics increasing in 48-72 hours

    • HgB will increase at 0.2-0.3 g/dl per day in first 3 weeks

  • MCV ↓ RDW nl

    • Thalassemia trait

  • MCV nl RDW nl

    • Acute anemia/chronic intercurrent illness

    • Transient erythrocytopenia (TEC)

  • MCV nl RDW ↑

    • Blood loss

    • Hemolytic anemia


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Use of MCV and RDW

  • MCV ↑ RDW ↑

    • Newborn

    • Incr retics

    • B12/folate def

    • Hypothyroidism

    • Liver disease

  • MCV ↑ RDW nl

    • Preleukemia

    • Leukemia

    • Aplastic anemia

    • Diamond-Blackfan syndrome

    • Down’s syndrome

    • Smoking


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Take home points

  • Coulter counter accurate but can give erroneous values under conditions like hypernatremia or hypertriglyceridemia

  • Only measured values are HgB, RDW, RBC, cell counts, and MCV

  • Remember to look closely at MCV/RDW as well as other indices for early diagnosis of major hematologic problems


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