L6: Full Blood Count Flashcards
(40 cards)
What is meant by normal/reference range?
The range within which 95% of healthy population can be expected to lie.
- Take sample of ‘healthy’ people
- Measure values
- Normal/refernce is 95% of these values (mean +/- 2 standard deviations)
If a result lies within the normal/reference range, does this mean it is normal?
Not necessarily. Could be a huge drop over short period of time, but both starting and end values are within range; would not be normal. Compare to previous results if possible.
State 4 factors that affect normal range
- Age
- Sex
- Ethnicity
- Co-morbidities
Why is reticulocyte count important in anaemia?
If patient has low Hb but high reticulocyte count it shows that body is trying to correct/compensate for the low Hb. If it is not you must investigate why.
Describe how RBC count works/is done in the lab
Automated cell counting (as cells pass single file through beam of ligth or electric current they interupt signal and this is one count)
Describe how WBC count works/is done in the lab
Automated cell counting (as cells pass single file through beam of ligth or electric current they interupt signal and this is one count AFTER RBC LYSIS)
Describe how Hb count works/is done in the lab
Lysis of RBCs followed by conversion of Hb to a stable form and then spectrophotometry (measures the amount of light absorbed which is proportional to the amount of absorbent compound, Hb, in it)
What is haeatocrit?
Fraction of whole blood volume that consists of RBCs
Describe the new and old way of measuring haematocrit in the lab
- New: mean cell volume x number of red cells per L
- Old: centrifuge blood sample & compare height of red cell fraction with heigh of total blood (=packed cell volume)
Define mean cell volume
Average volume of RBC measured in femtolitres
Describe how mean cell volume is calculated in lab
Shine light or electric current at a single line of cells and determine how much light is impeded/scattered; this is proportional to cell volume
Define mean cell haemoglobin
Average amount of Hb in one RBC
Describe how mean cell haemoglobuiin is calculated in lab
Hb in given volume of blood/number of RBC in same volume
Measured in picograms (also equal to femtokilograms)
Describe how platelet count works/is done in the lab
Automated cell counting (as cells pass single file through beam of ligth or electric current they interupt signal and this is one count)
Platelets much smaller hence their interuption of signal is much smaller so they can be easily distinguished between RBC & WBC
Describe how reticulocyte count works/is done in theh lab
Add special stains or fluroscent dye which bind to rRNA
Describe how differential white cell count works/is done in the lab
Automated blood analysers can recognise 5 types of normal WBC
How is a blood film prepared?
- Drop of blood at one end of slide
- Disperse blood using slider to get monolayer of cells
- Dry sample
- Fix in methanol
- Stain (to allow to distinguish different blood types)
- View under microscope
State 3 reasons/situations when blood films are used
- Assess cause of low or high counts
- Look for blood parasites (e.g. malaria)
- Check for abnormalites (e.g. sickle cell, spherocytosis, thrombocytopenic purpura)
Define red cell distribtuion width
Variation in size of RBC
Why must blood samples for FBC always be in a tube containing EDTA (pink top)?
EDTA chelates Ca2+ and acts as an anticoagulant as Ca2+ is very imporant in coagulationof blood. Blood cannot be analysed if it is clotted.
Why, if taking U&E’s, must you not pour blood from an FBC bottle into a U&E tube?
K+ salt of EDTA (which is used in FBC tube) would give very high K+ reading
Define normochromic/normocytic
No abnormal staining, characteristics or sizes
Define anisocytosis
Greater than normal variation in cell size
Define poikilocytosis
Greater than normal variation in cell shape
