The CBC in Pediatrics: A closer look

1. The CBC in Pediatrics: A closer look David Hilmers March 19, 2007

2. 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.

3. Coulter Counter

4. 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

5. 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

6. 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

7. Summary of Artifacts

8. 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?

9. 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

10. 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

11. 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?

12. 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.

13. What is a low MCV? • By age 1 lower limit of normal • MCV = Age (yrs) + 70

14. 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

15. Blood loss • Baby had bled out during delivery • Not hemodiluted yet • Needs circulatory support

16. 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?

17. 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

18. 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?

19. 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

20. 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?

21. 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

22. 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

23. 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

24. 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