Deciding what is normal and interpreting blood counts Flashcards Preview

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Flashcards in Deciding what is normal and interpreting blood counts Deck (29)
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1
Q

What is the relationship between altitude and normal ranges of Hb?

A

The higher the altitude, the higher the Hb

2
Q

How are reference and normal ranges determined and what’s the differences?

A
  • Reference ranges are determined from carefully defined reference populations, healthy with defined characteristics
  • Normal ranges is a vaguer concept - should represent people that live in the local area and come to the local hospital. Normal DOES not mean healthy e.g. UK high cholesterol is normal but unhealthy
3
Q

1) How can you determine ‘normal’ ranges with data following a Gaussian distribution?
2) Give an example of a data set following Gaussian distribution

A

1)

Take the mean and then do 2 S.D. on either side - this covers 95% of the data

2) Hb

4
Q

Give one example of a data set which does not follow Gaussian distribution

A

WBC count

5
Q

Give some caveats to determining a healthy range using the manipulation of data that follows Gaussian distribution and therefore suggest a good alternative

A
  1. Not all results outside the reference range are abnormal and not all results within the normal range are normal
  2. A result deemed ‘normal’ by this determination may still be unhealthy
  • A health-related range may be more meaningful
6
Q

What is WBC and what is the units for its measurement?

A
  • White blood cell count
  • x109/L
7
Q

What is RBC and what is the units for its measurement?

A
  • Red blood cell count
  • x1012/L
8
Q

What is Hb and what is the units for its measurement?

A
  • Haemoglobin concentration
  • g/L
9
Q

What is PCV and what is the units for its measurement?

A
  • Packed cell volume - the proportion of cells in the blood
  • l/l
  • As a fraction or percentage
10
Q

What is Hct and what is the units for its measurement?

A
  • Haematocrit - the ratio of RBC to blood
  • l/l
11
Q

What is the unit for measurement of platelet count?

A

109/L

12
Q

How are WBC, RBC and platelet count measured?

A

Automated machine counters - either through counting the number of electrical impulses generated when cells flow between a light source and a sensor or when cells flow through an electrical field

13
Q

How was Hb initially measured and how is it measured now?

A
  • Initially by spectrophotometry - measuring light absorption at various wavelengths
  • Now automated
14
Q

How were Hct and PCV initially measured?

A

Centrifugation

15
Q

How was MCV initially measured and how is it measured now?

A
  • Initially measured by dividing the total volume of red cells by the number of red cells (PCV / RBC)
  • Now determined indirectly by light scattering or interruption of an electrical field
16
Q

You can only measure MCV in a blood film if you what?

A

If you compare to a reference leukocyte

17
Q

Give a mathematical formula for MCH

A

MCH = Hb / RBC

18
Q

Give a mathematical formula for MCHC

A

MCHC = Hb / Hct

19
Q

How do cells with low MCHC appear?

A

Less red

20
Q

What is MCH and what are its units of measurement?

A
  • The absolute amount of Hb in an individual RBC (Hb/RBC)
  • picograms (x10-12)
21
Q

What is the unit of measurement for MCV?

A
  • Femtolitres (10-15)
22
Q

What is MCHC, what does it depend on and what are the units of measurement for MCHC?

A
  • Mean cell haemoglobin concentration - this is the concentration of Hb in a cell
  • MCHC is related to the shape of the cell
  • g/L
23
Q

1) What is polycythaemia?
2) Some markers that indicate polycythaemia?

A
  • Too many RBCs in circulation
  • High Hb, RBC, Hct
24
Q

What is pseudopolycythaemia and what is the difference between this and true polycythaemia?

A
  • Pseudopolycythaemia - decrease in plasma volume - so elevated Hb, RBC, Hct as in polycythaemia
  • In true polycythaemia, there is actual increase in number of circulating RBCs
25
Q

List the causes of polycythaemia (pseudo and true)

A

PSEUDOPOLYCYTHAEMIA

  • Reduced plasma volume

TRUE POLYCYTHAEMIA

  • Increase in circulating RBC due to:
  1. Blood doping or overtransfusion
  2. Appropriately increased erythropoietin - e.g. secondary to hypoxia
  3. Inappropriate increased erythropoietin - e.g. erythropoietin secreting renal tumour, illicit EPO administration
  4. Independent of EPO - e.g. bone marrow disorder ‘polycythaemia vera’
26
Q

1) What is polycythaemia vera - what is it a disease of and what class of disease is it?
2) Apart from elevated Hb, RBC and Hct, give one sign that may present with polycythaemia vera

A

1) Bone marrow - myeloproliferative neoplasm
2) Splenomegaly

27
Q

What might you suspect to be the cause of polycythaemia in the following patients:

1) A young, healthy athlete
2) A breathless, cyanosed patient
3) A patient with splenomegaly

A

1) Blood doping or illicit EPO use
2) Probably due to hypoxia causing increased erythropoietin
3) Polycythaemia Vera

28
Q

Why could true polycythaemia be a problem?

A

It can lead to hyperviscosity of the blood and in turn lead to vascular obstruction

29
Q

How to treat true polycythaemia?

A
  • If no physiological reason or if hyperviscosity is extreme - use venesection to remove blood to thin the blood
  • If there is an intrinsic bone marrow disease, drugs can be used to reduce the production of RBCs by the bone marrow