lecture 2 Flashcards
what does CBC stand for? what does it include?
CBC stands for complete blood count, includes:
- WBC count
- RBC count
- platelet count
- hemoglobin
- hematocrit
- MCV, MCH, MCHC
- RDW
- differential (automated/manual)
what is the name of the commonly used automated system?
model S coulter counter
what does the microhematocrit method determine? and what is the amount expressed as?
- determines maximum packing of the RBCs
- expressed as PCV, or Hct
what are the specimen requirements for a microhematocrit method?
- blood anticoagulated with EDTA or heparin
- use non-anticoagulated capillary tubes
- venous or capillary blood can be used
- special capillary tubes (coated with heparin) can be used to fill blood directly from the puncture site
why do we use non-anticoagulated capillary tubes?
- to avoid over-anticoagulation
- excess of anticoagulant can cause cell shrinkage
- lead to falsely low values
we use heparin, citrate, and EDTA for the whole blood used in the microhematocrit method (T/F)
false, we don’t use citrate
what are the pieces of equipment used in the microhematocrit method?
- non-graduated glass capillary tubes (can be lined with heparin for use with capillary blood or without heparin with previously anticoagulated venous blood)
- seal (clay) to seal one end of the tube
- special microhematocrit centrifuge
- Since the capillary tubes are not graduated, a special reading device is used to measure the % of packed RBCs (gives Hct directly as %)
what does the buffy coat consist of?
leukocytes and platelets
is the wintrobe method still used? and why?
- large amount of time & specimen required
- inaccurate due to the big amount of trapped plasma (greater than that found in the microhematocrit technique)
how does the macrohematocrit method measure hct/pcv?
- filling a wintrobe tube with whole blood
- centrifuging it for 30 minutes
- PCV was read from a scale on the tube
what is another name for the macrohematocrit technique?
wintrobe method
automated hct key points
- hct is obtained by an electronic cell counter
- it is calculated from the rbc count and mcv
- not directly measured
- not affected by the trapped plasma
- value will be lower than the value obtained from centrifugation
what is hemoglobin determination used for?
- measures the amount of hemoglobin in blood
- to see how much oxygen is being carried by RBCs
- used to screen for anemia…
relation between the oxygen-carrying ability of blood and Hb concentration
The oxygen-carrying ability of blood is directly proportional to its hemoglobin concentration
the number of RBCs indicates blood’s oxygen content (T/F)
false, the number of RBCs doesn’t indicate blood’s oxygen content because some cells may contain more Hb than others
what is the composite of hemoglobin in blood?
- oxyhemoglobin
- carboxyhemoglobin
- methemoglobin
- sulfmethemoglobin
what is carboxyhemoglobin composed of?
Hb combined with carbon monoxide
how to measure hemoglobin accurately in blood?
we should prepare a stable derivative containing all hemoglobin forms present
which hemoglobin derivative is abnormal? and why?
- sulfmethemoglobin
- not capable of transporting oxygen
(it is formed by the action of some drugs and chemicals such as sulfonamides)
+ methemoglobin (oxidation of Hb iron)
when is methemoglobin formed?
oxidation of Hb iron from the ferrous to the ferric state (incapable of carrying oxygen)
what is the name of the stable derivative? and what is it composed of?
- cyanmethemoglobin or hemoglobin cyanide
- composed of all hemoglobin forms except for sulfmethemoglobin
what is the process of forming cyanmethemoglobin?
- mixing a predetermined quantity of blood with potassium ferricyanide (K3 Fe (CN) 6) and potassium cyanide (KCN)
- potassium ferricyanide converts the Hb iron from the ferrous state (Fe++) to the ferric state (Fe+++) to form hemiglobin or methemoglobin (Hi)
-This combines with potassium cyanide to form Hemoglobincyanide (HiCN)
how does cyanmethemoglobin determine hemoglobin concentration?
Cyanmethemoglobin produces a color that is measured in a colorimeter, spectrophotometer (wavelength of 540nm), or automated instrument. The color relates to the concentration of hemoglobin in the blood
relation between absorbance and Hb concentration
absorbance is directly proportional to the concentration of Hb
C=A/K, what is K?
k is the constant for spectrophotometer
what is the concentration of Hb expressed as?
g/dl
what is the equation to calculate Hb concentration?
C=A/K
what are the RBC indices?
MCV, MCH, MCHC
what can be used to determine/calculate the RBC indices?
RBC count, Hb, Hct
what is the MCV? what is it expressed as?
- MCV (mean corpuscular volume) is the average size or volume of a single RBC
- expressed in femtoliters (fl)
- 1 ft= 10^-15 l
- previously expressed in micro m^3
what is the equation of MCV?
MCV = Hct (%) x 10 / RBC (10^12/L)
what is the normal range of MCV?
between 80-94 fl
MCV indicates whether the RBCs will appear:
Microcytic (if the MCV < 80 fl)
Normocytic (if MCV within normal range).
Macrocytic (if the MCV is > 100 fl)
MCV may fall within the normal range in the presence of microcytic and macrocytic cells at the same time (T/F)
true (however the RDW will be high)
what is the MCH? what is it expressed as?
- MCH (mean corpuscular hemoglobin) is the average weight of Hb per RBC
- expressed as picograms
- 1 pg= 10^-12 g
- previously expressed as micro micro g
what is the equation of MCH?
MCH = Hb(g/dl) x 10 / RBC (10^12/L)
what is the normal range of MCH?
27-31 pg
MCH indicates whether the RBCs will appear:
- Hypochromic (MCH<27pg)
- normochromic (normal range)
- high (MCH>31pg)
the MCH may be as low as 20pg or less in hypochromic microcytic anemia (T/F)
true
MCH is not affected in macrocytic anemias (T/F)
false, MCH is high in macrocytic anemias since the RBCs are larger and carry more Hb
when describing anemias, MCV, MCH, and MCHC, are most commonly used (T/F)
false, MCHC is rarely used while MCV, MCH are more commonly used
when describing anemias, MCV, MCH, and MCHC, are most commonly used (T/F)
false, MCHC is rarely used while MCV, MCH are more commonly used
what is MCHC? what is it expressed as?
- MCHC (mean corpuscular hemoglobin concentration) is the concentration of Hb in average RBC
- expressed as g/dl
- previously expressed as %
what is the equation of MCHC?
MCHC = Hb (g/dl) x 100 / Hct %
or
MCHC = MCH x 100 / MCV
what is the normal range of MCHC?
30-35 g/dl
values of MCHC <30 g/dl indicates hypochromia while >40 g/dl indicate high MCH (T/F)
false, MCHC cannot be >40 g/dl since RBCs cannot accommodate more Hb than 37 g/dl
(indicates malfunctioning of the instrument or error in calculation)
MCH and MCV vary together, and MCH and MCHC vary together (T/F)
false, MCV and MCHC vary together
in spherocytosis we have decreased MCV and elevated MCHC (T/F)
true
in megaloblastic anemia, the MCV is high but the MCHC is normal (T/F)
true
if MCV and MCH are low (microcytic and hypochromic), what type of anemias are classified?
- fe deficiency anemia
- thalassemia
if MCV and MCH are normal (normocytic and normochromic), what type of anemias are classified?
- ACD (anemia of chronic disease)
- structural hemoglobinopathies
if MCV and MCH are high (macrocytic), what type of anemias are classified?
megaloblastic anemia
what is RDW? what is it expressed as?
- RDW (red cell distribution width) measures the variation in RBC size
- expressed as %
what is anisocytosis?
anisocytosis –> elevated RDW
what does RDW help us determine?
- RDW is used along with other RBC indices, especially MCV to help determine the causes of anemia.
- Elevated RDW provides a clue for heterogeneous red cell size (anisocytosis) and/or the presence of 2 red cell populations
what types of anemias have a dimorphic RBC population?
- sideroblastic anemia
- fe deficiency anemia
- megaloblastic anemia
what laboratory tests are performed with an electronic cell counter?
- automated Hct
- RDW
what is the equation of RDW?
RDW (%) = 1 SD of the RBC Volume x 100/MCV
what is the reference range of RDW?
11-15%
in what condition is RDW useful?
- Elevated RDW helps in the diagnosis of early nutritional deficiency (iron, folate, vitamin B12 deficiency) as it becomes elevated earlier than
other RBC parameters. - distinguishes between uncomplicated iron deficiency anemia (elevated RDW, low MCV) and uncomplicated heterozygous thalassemia (normal RDW, low MCV)
what is the level of RDW in iron deficiency anemia? and why?
- Erythropoiesis is severely disrupted resulting in high RDW (anisocytosis)
- each developing erythrocyte grabs whatever Fe is available, some get more, most get less!
- => RBCs tend to vary in size.
what is the level of RDW in thalassemia? and why?
- normal RDW
- each erythrocyte has the same genetic defect, each makes the same reduced amount of hemoglobin
- each RBC is about the same size.
