Hematology Tests

Question 1

Some routine hematology tests

Answer 1

• complete blood cell count (CBC) +/- differential

- reticulocyte count

Question 2

Peripheral blood smears

Answer 2

• used for WBC + platelet estimates
• WBC differentials
• assessing morphology of all three cell lines
• ‘checking’ analyzer results
• EDTA anticoagulated whole blood (purple)

Question 3

Measuring Hb

Answer 3

• cyanmethemoglobin is reference method
• sodium lauryl sulfate method
• hemoglobin electrophoresis and HPLC

Question 4

Cyanmethemoglobin method

Answer 4

• whole blood diluted into an alkaline Drabkin’s reagent
  > Hb (Fe 2+) + potassium ferricyanide => methemoglobin (Fe 3+)
  > methemoglobin + potassium cyanide => cyanmethemoglobin (blue)
• measured using a spec (540 nm)
• cyanmethemoglobin is a stable pigment that follows Beer’s law (A proportional to c)
• result compared to a std curve

Question 5

sodium lauryl sulfate method

Answer 5

• SLS lyses RBCs = releases Hb
• SLS reacts with globin and oxidizes Fe 2+ to 3+
• SLS-Hb is measured spec

Question 6

Hb electrophoresis and HPLC

Answer 6

separates the different Hbs based on charge

Question 7

portion of the total blood volume that is occupied by RBCs

Answer 7

hematocrit

Question 8

manual procedure for determining the hematocrit

Answer 8

• capillary tube filled with blood
• tube is sealed and centrifuged
• special ruler used to measure the packed RBC volume

Question 9

Red cell indices

Answer 9

• calculated values
• used to describe the colour and size of RBCs
• MCV, MCH, MCHC

Question 10

mean cell volume

Answer 10

• measurement of avg size (vol) of RBCs
• femtoliters
• 1 fL = 10^-15 L
• normal = 80-100 fL; normocytic
• high = >100 fL; macrocytic
• low = <80 fL; microcytic
• MCV = Ht/RBC

Question 11

MCH

Answer 11

• avg weght of Hb in a RBC; gives clue to red cell size and colour
• picograms
• 1 pg = 10^-12 g
• normal = 26-35 pg
• high = >35 pg; macrocytic
• low = <26 pg; microcytes that are hypochromic (area of central pallor will be larger than normal if hypochromic)
• MCH = Hgb/RBC

Question 12

MCHC

Answer 12

• measure of avg conctn of Hb in each indiv red cell; gives clue to red cell colour
• g/L
• normal = 310-360 g/L = normochromic
• low = <310 g/L
• high = >360 g/L; spherocytes, agglutination, interference
• MCHC = Hgb/Ht

Question 13

modern cell counters aspirate blood directly from an EDTA tube

Answer 13

automated analyzers

Question 14

automated analyzers perform..

Answer 14

• RBC, WBC, and platelet counts + others
• calculates indices
• performs a 5 part (or more) differential

Question 15

optical scatter

Answer 15

• a sample stream is directed through a flow of cell and passes a focused light source
• cells are hit by a laser and interrupt the beam, causing light to scatter
• photodetectors detect the scattered rays
• many detectors at different angles may be used
  > forward scatter = size
  > side scatter = granularity
• histogram to differentiate various cell populations

NOTE: differentiates between cells based on size and light scatter

Question 16

electronic impedance

Answer 16

• detection and measurement of changes in electrical resistance as cells cross an aperture
• cells are suspended in an electrically conductive diluent (salient)
• # voltage pulses = proportional to # of cells
• height of pulse proportional to volume of cell
• histogram (# of cells vs. size of cells)

Question 17

RBC histogram

Answer 17

• MCV calculated using area under the curve
  > narrower the peak on the RBC histogram, the lower the variation in RBC size
• red cell distribution width (RDW) is a calculation in the variation of the RBC size
  > normal range = <15.6%