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Haematology > deciding what is normal > Flashcards

deciding what is normal Flashcards

1
Q

what is reference range *

A

range derived from a healthy reference population population

carefully derived

includes results from 95% of the healthy population`

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2
Q

what is normal range *

A

looser derivation than for reference range

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3
Q

what affects normal

A

age

gender

ethnic origin

physiological status - preg

altitude - affect Hb

nutritional status - difficult because not normal to be malnourished so do you include them?

nutritional status

smoking - affect WBC

alcohol - RBC larger and more

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4
Q

how is Hb conc affected by altitude *

A

higher = hypoxia = more erythropoitin = higher conc of Hb

have to derive reference range for people at that altitude

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5
Q

how is a reference range derived *

A

from a carefully defined reference population depending on age, gender etc

eg non-smokers

samples collected from healthy volunteers with defined characteristics

they are analysed using the instrument and techniques that will be used for pt samples because diff instruments wouldmake different results

the data are analysed using approproate techniques

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6
Q

how is a normal range defined *

A

much vaguer

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7
Q

what is an appropriate statistical technique to determine reference ranges *

A

data with normal (Guassian) distribution can be analysed by determing the mean and standard deviation and taking mean +/- 2SD as the 95% range

data with a different distribution must be analysed differently

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8
Q

what is teh distribution for Hb *

A

Gaussian

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9
Q

what is the distribution for WBC, what does this mean for stat investigations *

A

non-gaussian - tail of upper results

log distribution - replot with log = guassian

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10
Q

summarise caveats for determining the reference range *

A

not all normal results fall in reference range

not all results in normal range are normal - need to know if normal for person

a ‘normal’ result might still be bad for your health - a health related range may be more meaningful than a 95% range made using epi studies

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11
Q

what is the purpiose of a normal range *

A

to separate the normal people from thsoe that have something wrong with them - ideally there would be no cross over

bad if there is lots of cross over

in practice there will be a small amount of cross over

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12
Q

WBC = *

A

white blood cell count in given vol x10(9)/l

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13
Q

RBC = *

A

red blood cell count in a given vol of blood x10(12)/l

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14
Q

Hb *

A

haemoglobin conc g’l

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15
Q

MCV *

A

mean cell vol fl

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16
Q

MCH *

A

mean cell Hb pg

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17
Q

MCHC *

A

mean cell Hb conc g/l

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18
Q

platelet count *

A

number of platelets in a given vol of blood x10(9)/l

19
Q

how do you do a WBC, RBC and platelet count

A

used to be counted visually with a microscope and diluted blood

now automated - enumerating electronic impulses generated when cells flow between a light source and a sensor or when cells flow through an electric field

20
Q

how do you measure Hb

A

used to be by spectrometer by convertingHb to stable form (cyanmethaemoglobin) and measuring light absorption at a specific wave length

now automated - same principle

21
Q

how do you measure Hct

A

initially by centrifuging a sample

see % of column occupied by RBC

buffy coat is layer of white cells on top

now automated

22
Q

how do you calculate mean cell vol

A

initially by dividing HCT by RBC

now indirectly by light scattering/interruption of an electric field - larger cell scatter light more/more electrical disruption

23
Q

how do you work out mean cell Hb

A

amkunt of Hb in guven vol of blood/RBC in same vol

24
Q

how do you work out the mean cell Hb conc

A

Hb/Hct

25
Q

what is the difference between the MCH and MCHC *

A

increased MCV = increase MCH therefore normal MCHC

decreased MCV, = decrease MCH = normal MCHC

however if iron deficiency - the MCHC also decreases - cant make enough Hb

MCH is the absolute amount of Hb in individual red cell - measures average amount of Hb in individualred cell

in micro/macrocytic anaemia MCH parallels MCV

MCHC is related to the shape of the cell eg in spherocytosis - MCH stays the same, MCHC increases because same Hb in smaller vol

26
Q

illustrate scatter graphs for MCHC for

  • severe thalasssaemia
  • normal
  • hereditory spherocytosis *
A

–

27
Q

what blood film feature is associated with a low MCHC *

A

hypochromia

28
Q

process for interpreting a blood count *

A

is there leucocytosis/leucopenia? Why? Which cell line is abnormal, if reduced normally it is neutrophils? any clues in clinical history - eg infection

is there anaemia? any clues in blood count for anaemia? large or small cells? clinical history?

is there thrombocytosis or thrombocytopenia? any clues in blood count? clinical histry? eg high WBC and platelet suggest leukaemia

may also need to interpret blood film - eg this will allow you to see that sickle cell is the cause of the anaemia and the high platelet count because sickle cell reduces spleen function

29
Q

define polycythaemia *

A

literally means too many cells - but refers specifically to too many red cells in the circulation

the Hb, RBC, and Hct are all increased compared to someone of same age and gender (men higher Hb than women, adults higher than children)

30
Q

what are the causes of polycythaemia *

A

pseudo - reduced plasma vol - number of cells normal but the conc of Hb is high

true - increased total vol of red cells in circ - bloodd doping/over transfusion, appropriately raised erythropoitin becasue of hypoxia, innappropriate erythropoeitin synth or use, independant of erythropoeitin

31
Q

how do you interpret polycythaemia *

A

clinical history - splenomegaly indicate haemological abnormality meaning increased red cells, abdo mass indicate kidney secreting erythropoeitin inappropriately, cyanosis (blue) indicate hypoxia

compare with a normal range for appropriate altitude

Hb Hct and RBC are higher in neonate that children or adults

32
Q

how can polycythaemia be genuine or only apparent *

A

if it is due to decreased plasma vol, and high Hb is the only condition - might be becasue of dehydration - apparent polycythaemia

if there is an increase in number of circulating red cells - true polycythaemia - perhaps because of neoplastic condition - marrow make too many red cells

33
Q

what suggests blood doping

A

having blood from 2 different groups

too high Hb

34
Q

how can medical negligence cause polycythaemia *

A

give too much blood as a transfusion for the weight of the pt, and dont wait to see effect of 1st transfusion before repeating

cause v high Hb and so hypertension

35
Q

How can polycythaemia be caused by appropriately increased erythropoietin *

A

when live at altitude - need higher erythropoeitin and Hb because PO2 is lower

clubbing of fingers and cyanosis (blue colour) are signs of hypoxia

hypoxia due to cyanotic heart disease or severe chronic lung disease

36
Q

what is the risk of polycythaemia, why dont all people at altitude have polycythaemia *

A

it increases blood viscocity therefore chances of heart attack or stroke

so tibetan pop have a mutation that reduces erythropoeitin production in response to polycythaemia

37
Q

when is the cause of polycythaemia illicit *

A

when erythropoetin iss given to haematologically normal people

38
Q

when is endogenous erythropoietin inappropriate *

A

renal cysts/certain tumours inappropriately secretes erythropoetin = increase in Hb = polycythaemia

39
Q

how can abnormal function of the bone marrow cause polycythaemia *

A

inappropriately increased erythropoeisis that is independant of erythropoeitin

condition is an intrinsic bone marrow disorder - polycythaemia vera

it is classified as myeloproliferative neoplasm

there is a mutation in stem cells giving them a growth advantage = more red cells

this can lead to hyperviscosity = vascular obstruction = gangrene

40
Q

how can you treat polycythaemia *

A

if no need for igh Hb or ther eis high viscocity - remove the blood (venesection)

if there is intrinsic bone marrow disease, drugs can be used to reduce bone marrow production of red cells - in polycythaemia vera

41
Q

describe how different clinical info might help you interpret polycythaemia

  • young healthy athelete
  • breathless cyanosed patient
  • an abdominal mass
  • splenomegaly
A

athelete - suspicious

breathless - due to hypoxia

abdo mass - carcinoma of kidney

splen - pointer to polycythaemia vera (because more blood cells need to be fintered by the spleen)

42
Q

what factors can affect haematological variables *

A

altitude

smoking

alcohol

wether ambulent or resting

whether a tourniquet has been applied for a long time before taking sample

43
Q

when is polycythaemia physiological *

A

newborn

44
Q

what are the classifications of polycythaemia and examples *

A

physiological - newborn

appropriate erythropoetin secretion - when live at high altitude/hypoxic because of cyanotic heart disease, or severe chronic lung disease

inappropriate erythropoeitin secretion - eerythropoeitin abuse by atheletes or erythropoeitin produced by cysts or tumours

not due to erythropoeitin but due to intrinsic bone marrow disease - polycythaemia vera

Haematology (11 decks)

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