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Yr 2 MCD - Haem > 2 - Deciding What is Normal & Interpreting Blood Count > Flashcards

2 - Deciding What is Normal & Interpreting Blood Count Flashcards

1
Q

What factors can affect ‘normal’ blood ranges?

A
  • Age
  • Gender
  • Ethnic Origin
  • Physiological Status (e.g. pregnancy or not)
  • Altitude
  • Nutritional Status
  • Cigarette Smoking
  • Alcohol Intake
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2
Q

What happens to normal ranges of haemoglobin in blood at higher altitudes?

A

People living at high altitude have, on average, a lot more haemoglobin in their blood (g/l).

Hypoxia causes erythpoiesis, and therefore increased erythropoietin synthesis. Therefore, there is more haemoglobin in the blood due to having more RBCs.

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3
Q

What is the overall difference between a normal or reference range?

A

A reference range is derived from a carefully defined reference population.

  • specific criteria (e.g. nutritional status, age etc)
  • controls
  • study different populations

A normal range is a much vaguer concept.

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4
Q

How is a reference range determined?

A

Samples are collected from healthy volunteers with defined characteristics and circumstances (e.g. may also need to define time of day, fasting or not, rest/activity etc)

They are analysed using the instrument and techniques that will be used for patient samples

The data are analysed by an appropriate technique

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5
Q

What is an appropriate statistical technique for determining reference ranges?

A

NORMAL DISTRIBUTION
Data with a normal (Gaussian) distribution can be analysed by determining the mean and standard deviation and taking mean ± 2SD as the 95% range

DIFFERENT DISTRIBUTION
Data with a different distribution must be analysed by an alternative method

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6
Q

What kind of distribution does haemoglobin concentration in blood show?

A

Normal (Gaussian) Distribtution

  • as long as sample size is appropriate
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7
Q

What kind of distribution does WBC count show?

A

It is not normally distributed. It’s a logarithmic distribution.

  • tail at higher end
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8
Q

What are some caveats to the usefulness of reference ranges?

A
  • Not all results outside the reference range are abnormal
  • Not all results within the normal range are normal
  • A result within the 95% range determined from apparently healthy people may still be bad for your health (e.g. serum lipids in Western populations). In these cases, it’s better to have health-related ranges instead of a normal range.
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9
Q

What are the units for different measurements taken in a full blood count (FBC)?

A 
WBC = x10^9/l
RBC = x10^12/l
Hb = g/l (some textbooks use g/dl)
PCV = l/l
Hct = l/l 
MCV = fl
MCH = pg
MCHC = g/l (some textbooks use g/dl)
Platelet count = x10^9/l
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10
Q

How are WBCs, RBCs and platelets counted?

A

In large automated instruments. Done by enumerating electronic impulses generated when cells flow between a light source and a sensor or when cells flow through an electrical field

Used to be counted visually, using a microscope and a diluted sample of blood.

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11
Q

How is Hb measured?

A

Initially measured in a spectrometer, by converting haemoglobin to a stable form and measuring light absorption at a specific wave length (peak).

Now measured by an automated instrument but the principle is the same

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12
Q

How are PCV or Hct measured?

A

Initially measured by centrifuging a blood sample.

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13
Q

What does PCV stand for?

A

Packed Cell Volume

A measurement of the proportion of blood that is made up of cells.

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14
Q

How is MCV measured?

A

Initially calculated by dividing the total volume of red cells in a sample by the number of red cells in a sample, i.e. by dividing the PCV by the RBC

Now determined indirectly by light scattering or by interruption of an electrical field

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15
Q

What is the formula for MCV?

A

MCV (fl) =

PCV (l/l) x1000/RBC (x10^-12/l)

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16
Q

Rather than utilising advanced methods of calculating MCV, how else can it be recognised?

A

By looking at a blood film and noticing that blood cells are larger than normal.

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17
Q

How do you calculate MCH?

A

Amount of haemoglobin in a given volume of blood

divided by

Number of red cells in the same volume.

(i.e. the Hb divided by the RBC)

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18
Q

What is the formula for MCH?

A

MCH (pg) =

Hb (g/l) / RBC (x10^-12/l)

19
Q

How do you calculate MCHC?

A

Amount of haemoglobin in a given volume of blood

divided by

Proportion of the sample represented by the red cells

(i.e. the Hb divided by the PCV or haematocrit)

20
Q

What is the formula for MCHC?

A

MCHC (g/l) =

Hb (g/l) / Hct (l/l)

21
Q

What is the difference between MCH and MCHC?

A

The MCH is the absolute amount of haemoglobin in an individual red cell

In microcytic and macrocytic anaemias, the MCH tends to parallel the MCV

The MCHC is the concentration of haemoglobin in a red cell

22
Q

How do you interpret a blood count?

A 
To start with learn to interpret:
- WBC and differential
- Hb
- MCV
- Platelet count
Always look at the absolute count and not the percentage.

When you have mastered that, look at the other measurements also.

The correct interpretation may also require examination of a blood film.

1.
Is there leucocytosis or leucopenia?
If so, why?
Which cell line is abnormal?
Are there any clues in the clinical history?

2.
Is there anaemia?
If so, are there any clues in the blood count?
Are the cells large or small?
Are there any clues in the clinical history?

3.
Is there thrombocytosis or thrombocytopenia?
If so, are there any clues in the blood count?
Are there any clues in the clinical history?

23
Q

How would you interpret polycythaemia?

A

Refers specifically to too many red cells in the circulation.

The Hb, RBC and PCV/Hct are all increased compared with normal subjects of the same age and gender

24
Q

What are the causes of polycythaemia?

A 
PSEUDO
Reduced plasma volume
= Dehydrated
= Shock
= Chronic reduction in plasma volume

TRUE
Increase in total volume of red cells in the circulation
= Blood doping or overtransfusion
= Appropriately increased erythropoietin
= Inappropriate erythropoietin synthesis or use
= Independent of erythropoietin

25
Q

How do you evaluate polycythaemia?

A

Start with a clinical history and physical examination (splenomegaly, abdominal mass or cyanosis could be relevant)

Next compare with an appropriate normal range (needs to be relevant to age of patient).

Note: the Hb, RBC and Hct are higher in the neonate than at other times of life, lower in children than in adults and lower in women than in men.

26
Q

Why might an overtransfusion occur?

A

Due to medical negligence.

27
Q

What could cause erythropoietin to be appropriately raised in cases of True Polycythaemia?

A
  • People living at altitude.
  • In a response to hypoxia.

EXCEPTION:
Residents of the Tibetan plateau have a 85% prevalence of a mutation that reduces the erythropoietin production in response to hypoxia

28
Q

What could cause erythropoietin to be inappropriately raised in cases of True Polycythaemia?

A
  • Illegal erythropoietin usage

- Renal/Other tumour secretes erythropoietin

29
Q

What could cause erythropoietin independent cases of True Polycythaemia?

A

This condition is an intrinsic bone marrow disorder called polycythaemia vera.

It is erythropoeitin independent or largely independent.

It is classified as a myeloproliferative neoplasm

Can lead to ‘thick blood’ which is known as hyper viscosity. This can lead to vascular obstruction.

30
Q

How can polycythaemia be treated acutely?

A

If there is no physiological need for a high haemoglobin, or if hyperviscosity is extreme, blood can be removed to thin the blood

If there is intrinsic bone marrow disease (polycythaemia vera), drugs can also be used to reduce bone marrow production of red cells

31
Q

What is important to consider when interpreting a blood count?

A

Interpret it in the context of the clinical history and physical findings.

32
Q

Give some examples of how clinical context can help with interpreting a FBC that shows polycythaemia?

A

A young healthy athlete
- be very suspicious

A breathless cyanosed patient
‒ probably due to hypoxia

An abdominal mass
‒ it could be carcinoma of the kidney

Splenomegaly
‒ a pointer to polycythaemia vera

33
Q

If using a perfectly ideal statistical test, what results would you expect?

A

Two distinct Gaussian curves defining the ranges of certain values for sick and well people.

In practice, there is always overlap in ranges despite the health status of individuals.

34
Q

What is another name for Full Blood Count (FBC)?

A

Complete Blood Count

35
Q

What does each abbreviation on a FBC stand for?

A 
WBC = White Blood Cells
RBC = Red Blood Cells
HB = Haemoglobin
HCT = Haematocrit
MCV = Mean Cell Volume (Mean Corpuscular Volume)
MCH = Mean Cell Haemoglobin
MCHC = Mean Cell Haemoglobin Concentration
RDW = Red Cell Distribution 
PLT = Platelets
MPV = Mean Platelet Volume
NE = Neutrophils
LY = Lymphocytes
MO = Monocytes
EO = Eosinophils
BA = Basophils
36
Q

What is RDW in a FBC a measure of?

A

RDW = Red Cell Distribuion

It’s a measure of anisocytosis

37
Q

In what condition would you get a reduced MCH with normal MCHC?

A

Someone who is hemizygous for thalassemia

38
Q

In what condition does MCHC fall particularly?

A

In iron deficiency anaemia

Useful for suggesting the diagnosis

39
Q

What red cells have higher MCHC but normal MCH?

A

Spherocytes

40
Q

In polycythaemia vera, what can often be noticed on abdominal palpation?

A

Splenomegaly

41
Q

What would be the difference in a centrifuged blood sample between a normal sample and a Polycythaemia Vera sample?

A

Normal
: Hct = 30-40%

Polycythaemia Vera
: Hct = 80-90%
: Viscous blood

42
Q

What can be some serious complications of polycythaemia vera?

A

Vascular Obstruction

  • red hands
  • gangrene
  • MI
  • stroke
43
Q

Why can drugs given to patients with polycythaemia vera for reducing bone marrow activity be beneficial in other manners?

A

Reduce red blood cell production
- decrease hyperviscosity

May also reduce too much platelet production
- reduce risk of thrombosis

44
Q

What does the degree of blood thinning needed for each patient with polycythaemia depend on?

A

Amount of storage iron

  • continue thinning blood until storage iron is depleted
  • then it is easier to control the condition

Yr 2 MCD - Haem (12 decks)

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