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)
