3.2 -interpreting The Full Blood Count Flashcards
What percentage of the population is the normal range inclusive of?
95%. 2.5% of the population will have a greater normal result, 2.5% will have a lower normal result.
What factors affect normal range of FBC?
Age
Sex
Ethnicity
Co-morbidities
What 4 main errors can occur during obtaining pathology results?
Specimen collection (mix up, wrong bottle, pooling samples, poor technique)
Delivery of specimen to labatory (specimen delayed/not delivered, Wrong delivery method/ exposed to denaturing factors on delivery).
Specimen analysis and result reporting (mix up, wrong test performed/requested, incorrect clinical details, inherent test variability, technical error)
Responsive action (results not reviewed, reflex tests not carried out, right result applied to wrong patient)
What is the full blood count?
Panel of tests routinely performed on a blood sample in order to determine whether or not haematological defects are present.
An automated test which can accurately detect RBC, WBC and platelets.
What is spectrophotometry?
Amount of light absorbed by sample proportional to amount of absorbent compound within it. Used to measure haemoglobin. Hypotonic solution to lyse cells
What is flow cytometry?
Determines number of RBC and their size. Pass single file cells across a light beam. Measure the amount of light scattered/displaced.
What is flow cytometry differential?
Measure the sizes of cells.
Forward scatter = size
Side scatter = intracellular complexity
What are 3 FBC techniques?
Spectrophotometry
Flow cytometry
Flow cytometry differential
What is packed cell volume PCV?
Proportion of blood that is made up of RBC, centrifuged blood allows visualisation.
Assess anaemia and polycythemia.
What is EDTA and why is it present in blood sample tubes?
EDTA chelates Ca2+ ions and therefore acts as an anticoagulant. Without a chelating agent the blood sample would clot and be useless for analysis.
How is a white blood cell count determined?
Automated cell counting (interruption of a beam of light or electrical current as a line of single cells flow through a narrow tube) after the red blood cells have been lysed in the sample ( hypotonic solution used to lyse cells)
How is the red blood cell count determined?
Automated cell count without lysis step. White cells will also be counted but because they are so few in number this does not significantly affect RBC count.
What is haemoglobin concentration?
The amount of haemoglobin in blood (g/L)
How is haemoglobin concentration determined?
Determined by lysis of red cells followed by conversion of haemoglobin to a stable form and spectrophotometry.
What is spectrophotometry?
Spectrophotometry is a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution. Amount of light absorbed by sample proportional to amount of absorbent compound within it
What is haematocrit?
the fraction of whole blood volume that consists of red blood cells.
How is haematocrit measured?
Previously this was measured by centrifuging the blood sample and comparing the height of the red cell fraction with the height of the total blood (this would give the Packed cell volume (PCV)). Nowadays, replaced by the calculation of multiplying the average red cell size (the mean cell volume (MCV)) by the number of red cells per litre to give the Haematocrit.
What is corpuscular volume?
Mean cell volume. The average volume of red cells measured in femtolitres (10-15 litres).
How is corpuscular volume measured?
measured automatically by modern analysers (the amount of light or electric current impeded is proportional to the size of the cell)
