6. FBC Flashcards
What factors can affect normal range?
Age
Sex
Ethnicity
Co-morbidities
How should abnormal haematology results be interpreted?
Interpret in light of clinical context and previous FBC
E.g. acute/chronic change, explained by disease
Always ask, does it fit with the clinical scenario?
What errors in pathology results can come from specimen collection?
Specimen mix up Wrong blood in tube Wrong bottle Pooling samples Poor technique
What errors in pathology results can come from delivery of specimen to laboratory?
Specimen delayed/not delivered
Wrong delivery method
What errors in pathology results can come from specimen analysis and result reporting?
Specimen mix up Incorrect clinical details Wrong test requested/performed Inherent test variability (measurement uncertainty) Technical error
What are the concurrent parameters in the FBC?
Red cells - indices, RCC, haemoglobin
Platelets - count, size
White cells - count, full differential
What does pink top EDTA do?
Stops blood coagulation
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
Use calibration curve to determine sample concentration
What is flow cytometry?
Hydrodynamic focussing Single file line of cells pass through light beam Impedance counting Forward scatter = size More scatter = bigger cell
What is flow cytometry differential?
Forward scatter is size
Side scatter is mono/polymorphonuclear, intracellular complexity (granules)
Myloperoxidase activity
How is anaemia represented in blood sample?
Depressed hematocrit percentage
How is polycythemia represented in blood sample?
Elevated hematocrit percentage
Can be caused by reduction in circulating plasma volume or increased RBC
What is packed cell volume (PCV)?
Proportion of blood that is made up of RBC
Used to assess anaemia but more often polycythemia
What is RCC used for?
Used for assessment of anaemia and erytrocytosis
- reduced in iron deficiency anaemia
- increased in thalassemia trait
What is the mean cell volume (MCV)?
Mean RBC size, measured using amount of light scattered as they pass in a single file past a laser
Important parameter used to screen cause of anaemia
What is red cell distribution width (RDW)?
Variation in size of the RBC If increased = anisocytsis Used to help assess cause of anaemia - increased in iron deficiency - normal in thalassaemia trait - increased following transfusion
When is a blood film done?
When significant result outside of normal range, significant change within normal range, analyser thinks there are abnormal cells
What is the process of making a blood film?
Small drop of blood spread onto glass slide, 1 cell thick
Fixed with methanol
Stained to enable visualisation under microscope
What does hypochromia look like under microscope?
Less haemoglobin, more white in centre of cell
What does schistiocytes look like under microscope?
Red cell fragments present
What does a vitamin B12 deficiency look like under the microscope?
Oval macrocytes Basophils stippling Howell-Jolly bodies Hypersegmented neutrophil Circulating granulocytic precursors
