Red blood cell indices

Question 1

manual hematocrit

Answer 1

• centrifuge whole blood
• HCT = packed red cell column height : total height

Question 2

Hemocytometer

Answer 2

• etched glass chamber with raised sides exactly 0.1 mm in depth
• surface area of 9 mm²
• 1 large square has a volume of 0.0001ml
• RBCs, WBCs, and platelets counted manually

Question 3

MCV =

Answer 3

Hct x 10 / RBC

(MCV expressed in fL)

Question 4

MCHC =

Answer 4

Hgb/Hct x 100

Question 5

Automated red cell indices methods

Answer 5

• Methods
  
  • impedance
  • optical
  • radiofrequency
  • conductivity
• lowest precision for platelet count
• incapable of counting bands
• not great at counting basophils
• offers flags (blasts, nRBCs, immature granulocytes)
• high sensitivity, low specificity

Question 6

automated hemoglobin measurement

• method
• interference?

Answer 6

• cyanohemoglobin/hemoglobin cyanide (HiCN) method
  
  • lysed blood dissolved in a solution of potassium ferricyanide and potassium cyanide
  • oxidizes Hb to hemoglobin cyanide (HiCN)
  • concentration of HiCN measured by spectrophotometry
  • absorbance at 540 nm reflects the amount of hemoglobin
  • detects all forms of hemoglobin except sulfhemoglobin
  • lipidemia and paraproteinemia can falsely raise the hemoglobin measurement

Question 7

automated cell counts

• method
• size of particles (RBC, WBC, platelets)
• RBCs versus leukocytes
• platelets

Answer 7

• impedance counting
• particles 36 - 360 fL are counted as red cells
  
  • leukocytes are within this size range; usually their effect is negligible unless count very high
• following red cell lysis, particles > 36 fL coutned as leukocytes
• platelets are counted as particles <36 fL
  
  • falsely low platelet counts may result if platelets are large or clumped

Question 8

automated MCV and RDW measurements (also MPV and platelet distribution, Hct, MCHC)

Answer 8

• Determined with stats
• Red cells distribute in a Gaussian fashion according to size
  
  • Mean of this distribution is the MCV
  • RDW is the coefficient of variation in the curve
• MPV and platelet distribution width can be calculated in a similar way
• from there Hct and MCHC are calculated

Question 9

high MCHC

• range
• is indicative of

Answer 9

• 32-36%
• spherocytosis
• cold agglutinins
• lipemic specimens

Question 10

Counting reticulocytes

• difference between reticuloctye and mature RBC
• techniques
• absolute retic count =
• corrected retic count =
• reticulocyte production index (RPI)

Answer 10

• differentiation of reticulocytes from mature red cells based upon abundance of ribosomal RNA in the reticulocytes
• Techniques: manual counting and automated (optical light scatter and flow)
  
  • supravital dye (methylene blue or azure B) highlights RNA
• Absolute reticulocyte count = % reticulocytes x RBC count
• Corrected reticulocyte count (CRC)= % reticulocytes x Hct/45
• Reticulocyte production index (RPI) = CRC x 1/maturation index

Question 11

Answer 11

Question 12

Answer 12

Question 13

Answer 13