Interpreting the full blood count Flashcards
what is an FBC
panel of tests routinely performed on blood sample to determine prescne of haematological abnormalities - performed on automated analysers
what tube should sample be placed in
- containing k-EDTA
- it chelates calcium ions so acts as an anticoagulant
urea and electrolyte analysis
never pour blood from FBC tube into UE tube as K+ of k-EDTA will provide extremely high K+ reading
what is an abnormal result
- falls outside the normal range of values
- drastically different to a previous result
normal range
- only includes 95% of normal helathy population
- changes with age, sex, ethnicity and co-morbidities
- interpreted alongside good history and examination
FBC analyser
- closed system
- easy to maintain
- cope with high numbers of samples
errors in processing a FBC
specimen collection
- wrong blood in tube
- wrong bottle - wrong agents for the test
- pooling samples
- poor technique or heavy handling - triggers clotting cascade
delivery of specimen to laboratory
- specimen delayed, not delivered or lost
- wrong delivery method e.g. temperature
specimen analysis and result reporting
- specimen mix up
- incorrect clinical details
- wrong test requested/performed
- inherent test variability - analysers not 100%
- technical error
responsive action
- result not reviewed
- reflex tests not carried out
- right result applied to wrong patient
components of FBC
- white blood cell count (WBC)
- red blood cells count (RBC)
- haemoglobin concentration (Hb)
- haematocrit (HCT)
- mean cell volume (MCV)
- mean cell haemoglobin (MCH)
- platelet count
- reticulocyte count
- differential white blood cell counts
analyser techniques
spetrophotometry
- amount of light absorbed by sample proportional to amount of absorbent compound - measures Hb
- hypotonic solution to lyse cells
- conversion to universal Hb derivative
- calibration curve
flow cytometry
- single file line of cells through light beam
- impedance counting
- forward scatter = size
- more scatter = bigger cell
white blood cell count (WBC)
- aka leukocytes - immune system cells
- automated cell counting (interruption of beam of light/current as line of single cells flow through tube) after RBCs lysed
- increase: infection, smoking, leucocytosis, imune system disorders
- decrease: damaged bone marrow, antibiotics, chemotherapy
red blood cell count (RBC)
- number of RBC in given volume of blood
- same method as WBC (light beam) without lysis step
- increase: congentinal causes, hypoxia, polycythaemia vera
- decrease: anaemia, bleeding, erythropoietin deficiency
what is haematocrit (HCT)
fraction of whole blood volume that consists of RBC
how is haematocrit measured
multiply mean cell volume by number of red cells per litre
haemoglobin concentration (Hb)
- amount of Hb in blood g/L
- lysis of RBC then conversion of Hb to stable form and colorimeter
- increase: high altitudes, lung dysfunction
- decrease: dietary iron deficiency, vitamin B12/folate deficiency, bleeding, anaemia
what is mean cell volume (MCV)
average volume of red cells (measured in fl)
how is MCV measured
use beam of light/current and assess amount that is bloked by red cells
increased MCV (macrocytic anaemia) causes
>100 fl
- megaloblastic anaemia
- liver disease
- alcohol, smoking
- haemolytic anaemia
- hypothyroidism
- drugs (HIV drugs, hydroxycarbamide, methotrexate)
- myelodysplasia
- myeloma
decreased MCV (microcytic anaemia) causes
< 80 fl
- iron deficiency anaemia
- thalassaemia
- anaemia of chronic disease
what is mean cell haemoglobin (MCH)
average amount of Hb in an individual RBC
how is MCH measured
divide Hb concentration by number of red cells in a given volume
abnormal MCH levels
- increase: macrocytic anaemia, vitamin B12/folate deficiency
- decrease: microcytic anaemia, iron deficiency, thalassaemia
platelet count
- involved in clotting
- measured same way as red and white cells - produce smaller signal so easily distinguished
- increase: thrombocytosis, bone marrow disorders
- decrease: increased platelet destruction
reticulocyte count
- measurement of immature RBCs
- stains and dyes that bind to rRNA used
significance of reticulocyte count
- useful in evaluating different kinds of anaemia
- measure of how bone marrow is working
abnormal reticulocyte count
- increase: haemolytic anaemia, bleeding, response to iron/B12/ folate supplement, response to EPO, recovery from bone marrow suppression
- decrease: haematinic deficiency, bone marrow failure, parvovirus infection
differential white blood cell counts
- recognise numbers of different white cells
- neutrophils, lymphocytes, basophils, eosinophils, monocytes
- counted manually on blood film if abnormalities detected
how is a blood film created
- drop of blood placed on glass slide
- spread until it is one cell layer thick so cells easily viewed under microscope
- air dry the sample
- fix the film with methanol to prepare for staining and protect from infectious diseases
- stain with methylene blue and eosin dyes for clear visualisation
what are blood films used for
- assess causes of low or high counts
- look for blood parasites e.g. malaria, filariasis
- check for abnormalities such as sickle cell, spherocytosis, thrombotic thrombocytopenic purpura (TTP)
normocytic + normochromic
normal sized + colour
macrocytic
abnormally large cells
microcytic
abnormally small cells
hyperchromic
densely packed Hb in cell - appears darker
hypochromic
less Hb in cell - appears lighter and paler
dimorphism
two populations of RBCs
anisocytosis
increased variation in size
poikilocytosis
increased variation in shape
spherocytosis
spherical RBC lacking central pallor
elliptocytosis
elliptical RBC
irregularly contracted cells
small dense RBCs not as regular as spherocytes shape
sickle cells
crescent shaped RBCs
target cell (codocytes)
Hb concentrated at centre and periphery
stomatocytes
pale slit in centre of RBC - bowl shaped
schistocytes
red cell fragments
acanthocyte (spur cell)
RBCs have irregular cell membrane with small number of spiky protrusions
echinocyte (crenated cell)
RBCs have irregular cell membrane with large number of spurs
agglutination
RBCs clumped together
Howell-Jolly bodies
DNA or nuclear fragments in RBCs
basophilic stippling
RNA inclusions in RBCs
pappenheimer bodies
iron inclusions in RBCs
Heinz bodies
clumps of denatured haemoglobin in RBCs
blister cells
empty pocket at edge of RBC consistent with oxidative haemolysis + G6PDH deficiency
