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MEH > Interpreting the full blood count > Flashcards

Interpreting the full blood count Flashcards

1
Q

what is an FBC

A

panel of tests routinely performed on blood sample to determine prescne of haematological abnormalities - performed on automated analysers

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2
Q

what tube should sample be placed in

A
  • containing k-EDTA
  • it chelates calcium ions so acts as an anticoagulant
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3
Q

urea and electrolyte analysis

A

never pour blood from FBC tube into UE tube as K+ of k-EDTA will provide extremely high K+ reading

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4
Q

what is an abnormal result

A
  • falls outside the normal range of values
  • drastically different to a previous result
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5
Q

normal range

A
  • only includes 95% of normal helathy population
  • changes with age, sex, ethnicity and co-morbidities
  • interpreted alongside good history and examination
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6
Q

FBC analyser

A
  • closed system
  • easy to maintain
  • cope with high numbers of samples
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7
Q

errors in processing a FBC

A

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

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8
Q

components of FBC

A
  • 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
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9
Q

analyser techniques

A

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

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10
Q

white blood cell count (WBC)

A
  • 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
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11
Q

red blood cell count (RBC)

A
  • 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
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12
Q

what is haematocrit (HCT)

A

fraction of whole blood volume that consists of RBC

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13
Q

how is haematocrit measured

A

multiply mean cell volume by number of red cells per litre

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14
Q

haemoglobin concentration (Hb)

A
  • 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
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15
Q

what is mean cell volume (MCV)

A

average volume of red cells (measured in fl)

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16
Q

how is MCV measured

A

use beam of light/current and assess amount that is bloked by red cells

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17
Q

increased MCV (macrocytic anaemia) causes

A

>100 fl
- megaloblastic anaemia
- liver disease
- alcohol, smoking
- haemolytic anaemia
- hypothyroidism
- drugs (HIV drugs, hydroxycarbamide, methotrexate)
- myelodysplasia
- myeloma

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18
Q

decreased MCV (microcytic anaemia) causes

A

< 80 fl
- iron deficiency anaemia
- thalassaemia
- anaemia of chronic disease

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19
Q

what is mean cell haemoglobin (MCH)

A

average amount of Hb in an individual RBC

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20
Q

how is MCH measured

A

divide Hb concentration by number of red cells in a given volume

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21
Q

abnormal MCH levels

A
  • increase: macrocytic anaemia, vitamin B12/folate deficiency
  • decrease: microcytic anaemia, iron deficiency, thalassaemia
22
Q

platelet count

A
  • 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
23
Q

reticulocyte count

A
  • measurement of immature RBCs
  • stains and dyes that bind to rRNA used
24
Q

significance of reticulocyte count

A
  • useful in evaluating different kinds of anaemia
  • measure of how bone marrow is working
25
Q

abnormal reticulocyte count

A
  • 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
26
Q

differential white blood cell counts

A
  • recognise numbers of different white cells
  • neutrophils, lymphocytes, basophils, eosinophils, monocytes
  • counted manually on blood film if abnormalities detected
27
Q

how is a blood film created

A
  • 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
28
Q

what are blood films used for

A
  • 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)
29
Q

normocytic + normochromic

A

normal sized + colour

30
Q

macrocytic

A

abnormally large cells

31
Q

microcytic

A

abnormally small cells

32
Q

hyperchromic

A

densely packed Hb in cell - appears darker

33
Q

hypochromic

A

less Hb in cell - appears lighter and paler

34
Q

dimorphism

A

two populations of RBCs

35
Q

anisocytosis

A

increased variation in size

36
Q

poikilocytosis

A

increased variation in shape

37
Q

spherocytosis

A

spherical RBC lacking central pallor

38
Q

elliptocytosis

A

elliptical RBC

39
Q

irregularly contracted cells

A

small dense RBCs not as regular as spherocytes shape

40
Q

sickle cells

A

crescent shaped RBCs

41
Q

target cell (codocytes)

A

Hb concentrated at centre and periphery

42
Q

stomatocytes

A

pale slit in centre of RBC - bowl shaped

43
Q

schistocytes

A

red cell fragments

44
Q

acanthocyte (spur cell)

A

RBCs have irregular cell membrane with small number of spiky protrusions

45
Q

echinocyte (crenated cell)

A

RBCs have irregular cell membrane with large number of spurs

46
Q

agglutination

A

RBCs clumped together

47
Q

Howell-Jolly bodies

A

DNA or nuclear fragments in RBCs

48
Q

basophilic stippling

A

RNA inclusions in RBCs

49
Q

pappenheimer bodies

A

iron inclusions in RBCs

50
Q

Heinz bodies

A

clumps of denatured haemoglobin in RBCs

51
Q

blister cells

A

empty pocket at edge of RBC consistent with oxidative haemolysis + G6PDH deficiency

MEH (26 decks)

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