Interpreting the full blood count

Question 1

what is an FBC

Answer 1

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

Question 2

what tube should sample be placed in

Answer 2

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

Question 3

urea and electrolyte analysis

Answer 3

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

Question 4

what is an abnormal result

Answer 4

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

Question 5

normal range

Answer 5

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

Question 6

FBC analyser

Answer 6

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

Question 7

errors in processing a FBC

Answer 7

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

Question 8

components of FBC

Answer 8

• 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

Question 9

analyser techniques

Answer 9

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

Question 10

white blood cell count (WBC)

Answer 10

• 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

Question 11

red blood cell count (RBC)

Answer 11

• 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

Question 12

what is haematocrit (HCT)

Answer 12

fraction of whole blood volume that consists of RBC

Question 13

how is haematocrit measured

Answer 13

multiply mean cell volume by number of red cells per litre

Question 14

haemoglobin concentration (Hb)

Answer 14

• 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

Question 15

what is mean cell volume (MCV)

Answer 15

average volume of red cells (measured in fl)

Question 16

how is MCV measured

Answer 16

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

Question 17

increased MCV (macrocytic anaemia) causes

Answer 17

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

Question 18

decreased MCV (microcytic anaemia) causes

Answer 18

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

Question 19

what is mean cell haemoglobin (MCH)

Answer 19

average amount of Hb in an individual RBC

Question 20

how is MCH measured

Answer 20

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

Question 21

abnormal MCH levels

Answer 21

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

Question 22

platelet count

Answer 22

• 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

Question 23

reticulocyte count

Answer 23

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

Question 24

significance of reticulocyte count

Answer 24

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

Question 25

abnormal reticulocyte count

Answer 25

- **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

Question 26

differential white blood cell counts

Answer 26

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

Question 27

how is a blood film created

Answer 27

- 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

Question 28

what are blood films used for

Answer 28

- 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)

Question 29

normocytic + normochromic

Answer 29

normal sized + colour

Question 30

macrocytic

Answer 30

abnormally large cells

Question 31

microcytic

Answer 31

abnormally small cells

Question 32

hyperchromic

Answer 32

densely packed Hb in cell - appears darker

Question 33

hypochromic

Answer 33

less Hb in cell - appears lighter and paler

Question 34

dimorphism

Answer 34

two populations of RBCs

Question 35

anisocytosis

Answer 35

increased variation in size

Question 36

poikilocytosis

Answer 36

increased variation in shape

Question 37

spherocytosis

Answer 37

spherical RBC lacking central pallor

Question 38

elliptocytosis

Answer 38

elliptical RBC

Question 39

irregularly contracted cells

Answer 39

small dense RBCs not as regular as spherocytes shape

Question 40

sickle cells

Answer 40

crescent shaped RBCs

Question 41

target cell (codocytes)

Answer 41

Hb concentrated at centre and periphery

Question 42

stomatocytes

Answer 42

pale slit in centre of RBC - bowl shaped

Question 43

schistocytes

Answer 43

red cell fragments

Question 44

acanthocyte (spur cell)

Answer 44

RBCs have irregular cell membrane with small number of spiky protrusions

Question 45

echinocyte (crenated cell)

Answer 45

RBCs have irregular cell membrane with large number of spurs

Question 46

agglutination

Answer 46

RBCs clumped together

Question 47

Howell-Jolly bodies

Answer 47

DNA or nuclear fragments in RBCs

Question 48

basophilic stippling

Answer 48

RNA inclusions in RBCs

Question 49

pappenheimer bodies

Answer 49

iron inclusions in RBCs

Question 50

Heinz bodies

Answer 50

clumps of denatured haemoglobin in RBCs

Question 51

blister cells

Answer 51

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