6.2 - Blood Count and Films Flashcards
reference ranges (in general)
- results outside of the normal ranges are abnormal
- normal range only includes 95% of the population
- some people’s ‘baseline’ is normal for them, despite it being slightly below the ‘normal’ reference
- significant fall in value can also be abnormal, even if the drop still sits within the reference range
- normal range changes with…
age, sex, co-morbidities etc - abnormal haematology results often reactive rather than reflective of an underlying haematological disorder
- interpret results in light of clinical context and previous FBC
what are some errors in lab results
technically not on LOs
specimen collection
- specimen mix-up
- wrong bottle
- pooling of samples
- poor technique
delivery of specimen to lab
- specimen delayed or not delivered
- wrong delivery method eg some samples need to be in ice or in the dark
analysis and result reporting
- specimen mix-up
- incorrect clinical details
- wrong test requested
- inherent test variability (due to how analysers work)
- technical error
responsive error
- results are not reviewed
- right result applied to wrong patient
what must the blood be anticoagulated with
k-EDTA
this stops blood coagulation
carrying out a FBC: the analysers
- automated
- closed system
- able to cope with high numbers of specimens
- greater accuracy
- results for essential parameters, eg red cells, platelet count and size, and white cells
analyser technique - spectrophotometry
- amount of light absorbed by sample proportional to amount of absorbent compound within it
- used to measure the amount of haemoglobin
- more haemoglobin, the more light absorbed, the less light transmitted
- hypotonic solution to lyse cells
- uses calibration curve to measure sample concentration
analyser technique - flow cytometery
- for measuring cell count and characteristics
- hydrodynamic focussing
- single file line of cells pass through light beam
- impedance counting: every time it detects a cell, it disrupts light
- can measure the ‘forward scatter’ ie how the light is refracted, in order to measure the size of cell
what tests can be carried out for white blood cells
- flow cytometery to determine size and complexity
- ‘side scatter’ measures how complex cells are, eg mono/polymorphonuclear and presence of granules
- WBC count can be increased for numerous reasons
- 5 part differential: neutrophils, eosinophils, basophils, lymphocytes and monocytes
what is PCV / Hct
PCV = packed cell volume
Hct = haemocrit
- both measure the same thing
- proportion of blood that is made up RBC
- this can be visualised using centrifugation
- used to asses polycythaemia (excessive RBCs)
- guides diagnosis and treatment
what are the 4 main components of blood
- plasma
- white blood cells
- red blood cells
- platelets
what is Hb
Hb = haemoglobin
- measured in g/L
- concentration of haemoglobin in blood (not quanitity)
reference ranges vary between labs but generally less than….g/L in….
- 135 in adult men
- 115 in adult women
- 110 in children
- 150 in newborns
note that lab parameters affect results
- eg turbid plasma where there is high lipid content in blood (eg just after McDonald’s) which absorbs light as well as haemoglobin… causes Hb overestimate
- eg in vitro haemolysis causes Hb underestimate
what is RCC
RCC = red cell count
- number of RBC in given volume of blood
- measured by impedance counting
- units are x10^12 / L
- used for assessment of anaemia and eryhtrocytosis…
microcytic anaemia
- RRC is reduced in iron deficiency anaemia
- increased in thalassemia trait
erythrocytosis
- if RCC is elevated, more likely to be true polycythaemia
- spurious polycythaemia ★ caused by decreased plasma volume, RCC won’t be increased
★ changes in plasma volume causes problems, not cells
what is MCV
and give some examples of when it might be increased or decreased
mean cell volume
- the most important parameter to determine cause of anaemia
- measured in fL
increased in…
- megaloblastic anaemia
- liver disease
- alcohol and smoking
- haemolytic anaemia (due to larger size of reticulocytes)
- hypothyroidism
- drugs (esp HIV drugs, hydroxycarbamide, methotrexate)
- myelodysplasia
- myeloma
reduced in
- iron deficiency anaemia
- thalassaemia
- anaemia of chronic disease
patient history is important
what is RDW
red cell distribution width
- measured by %
- variation in size of RBC
- if increased = anisocytosis
- used to help assess cause and timeline of anaemia…
→ increased in developing/recently treated iron deficiency ★
→ normal in thalassaemia trait
→ increased during haemolysis (reticulocytes)
★ iron deficiency makes RBCs smaller, causing developing iron dificiency, which causes a wider distribution in width, and this causes an increase in RDW
what is RDW
red cell distribution width
- measured by %
- variation in size of RBC
- if increased = anisocytosis
- used to help assess cause and timeline of anaemia…
→ increased in developing/recently treated iron deficiency ★
→ normal in thalassaemia trait
→ increased during haemolysis (reticulocytes)
★ iron deficiency makes RBCs smaller, causing developing iron dificiency, which causes a wider distribution in width, and this causes an increase in RDW
what is MCH
mean cell haemoglobin
- measured in pg
- average measure of the amount of Hb in each RBC
- calculated by Hb ➗ RCC
- used in assessment of anemia
usually…
- reduced in iron deficiency
- reduced in thalassaemia
- reduced in haemoglobinopathy
- increased in macrocytic anaemias
- normal in mixed deficiency (averages out reduction and increase)
what is reticulocyte count
- reticulocytes are immature blood cells
- should be high sometimes
- measurement of the number of young erythrocytes
- identified using size and RNA content
- units are x10^9 / L
increased in
- haemolytic anaemia
- recent blood loss ★
- response to iron, vit B12, folate replacement
- response to EPO
- recovery from bone marrow suppression
reduced in
- haematinic deficiency
- bone marrow faliure
- parovirus infection
★ recent blood loss: hopefully should be increased reticulocyte count, as it shows that bone marrow is pushing RBCs down maturation
same with anaemia….
high RC shows that bone marrow is trying to recover from this
what is a blood film and why are they used
- FBC result is abnormal, it is flagged
- eg results outside of normal ranges, abnormal cells (immature cells, parasites, unidentifiable)
- blood film reviewed by biomedical scientist, who passes onto haematologist if any concerns
- medical comments at the end often suggesting additional tests
- results in a delay in authorisation
what does microcytic and macrocytic mean
used in MCV (mean cell volume) tests
microcytic = small
macrocytic = large RBC
what is anicytosis
used in MCV (mean cell volume) tests
means there is an increased variation in size of red blood cells
causes for this on previous cards
what does hypochromic and hyperchromic mean
used in MCH (mean cell haemoglobin) tests
hyperchromic = dense, more Hb in given volume
hypochromic = pale, less Hb
what is dimorphism
used in mean cell volume (MCV) and mean cell haemoglobin (MCH) tests
means that there are two distinct populations of red cells in the blood film… ie two different appearances of cells. eg post transfusion
what cells are polychromatic on blood film
reticulocytes
they appear purple due to two different stains and two different colours
what does poikilocytosis, spherocytosis and elliptocytosis mean
poikilocytosis is an abnormally shaped RBC
spherocytosis is a spherical shaped RBC
elliptocytosis is an elliptical RBC
what is an irregularly contracted cell
- small and dense RBC
- not as regular in shape as spherocytes
- lack central pallor
- haemoglobin appears condensed and irregularly distributed in the RBC
what are common words used to describe spiculated cells
spiculated = spiny
- echinocytes
- acanthocytes
- keratocytes
very subtle differences between these
what are schistocytes
red cell fragments
what are sickle cells
crescent or sickle shaped cells seen in sickle cell disease
what are target cells
RBC with dark area in the middle of the area of central pallor
looks like a bullseye target
what are blister cells
and when might they be present
empty pocket at the edge of the red cell
consistent with oxidative haemolysis/G6PD deficiency
some examples of RBC inclusions
FOR REFERENCE ONLY, not in LOs
- howell-jolly bodies are DNA/nuclear fragments
- basophilic stippling are RNA inclusions
- pappenheimer bodies are iron inclusions
- heinz bodies are denatured haemoglobin
- haemoglobin H inclusions are beta chain tetramers found in severe alpha thalassaemia
