MEH 6 - Blood Films

Question 1

How are normal references ranges/abnormal results determined?

Answer 1

• Normal reference range on bell curve includes 95% of health population. 2.5% below this, and 2.5% above this are the “abnormal range”
• However, results within the normal range can also be abnormal - if there is a significant drop in value.
• Remember, normal range changes w/age, sex, ethnicity etc.

NB: Always treat the patient, not the result.

Question 2

Are abnormal haematology results reactive or reflective of an underlying haematological disorder?

Answer 2

• Usually reactive than reflective - ie.: usually being caused by underlying haematological disorder.
• Interpret in light of clinical situation, patient history and previous FBC results.

Question 3

What are the 4 potential sources of errors in pathology results? Give examples of each.

Answer 3

1) Specimen collection - e.g.: specimen mix up, pooling samples, poor technique
2) Delivery of specimen to lab- e.g.: specimen delayed/not delivered properly
3) Specimen analysis + result reporting - e.g.: wrong test performed, inherent test variability, technical error
4) Responsive action - e.g.: result not viewed, right result applied to wrong patient etc.

Question 4

What is a full blood count (FBC) test and its essential parameters?

Answer 4

• An automated test, essential parameters are red cells, platelets and white cells.

Question 5

What analyser techniques are used to obtain an FBC?

Answer 5

1) Spectrophotometry - amount of light absorbed used as a measurement, after hypotonic solution used to lyse cells. Use calibration curve to determine sample concentration.
2) Flow cytometry - used mostly to count number of red cells + determining their size. Single file line of cells, forward scatter measures size. Also used to look at intracellular features. Side scatter is used to look at this.

Question 6

What is “packed cell volume” (PCV)?
What is it used to assess?
What is the normal haematocrit range in men and women?

Answer 6

• HCT = haematocrit (proportion of blood made up of RBC’s)
• Used to assess anaemia, but more often polycythaemia (PCV is increased/needs to be reduced).
• 37-47% for women, 42-52% for men

Question 7

What are the general reference ranges for Hb in men and women?
What can affect Hb measurements?

Answer 7

• > 135g/L men, >115g/L women

- Turbidity of plasma, in-vitro haemolysis.

Question 8

What is the red cell count (RCC)

What is this measurement used to assess?

Answer 8

• Number of RBC’s in a given volume of blood

- Anaemia + erythrocytosis

Question 9

What is mean cell volume? (MCV)
What is it an important parameter for?
In what situations is MCV high + low?

Answer 9

• Mean size of RBC’s
• Important parameter to screen cause of anaemia
• High in megoblastic anaemia, liver disease, alcohol drinkers/smokers, myeloma etc.
• Low in iron deficiency anaemia, thalassaemia.

Question 10

What is mean cell haemoglobin? (MCH)

What is it used for assessment of?

Answer 10

• Average measure of the amount of Hb in each RBC

- Used in assessment of anaemia, reduced in iron deficiency, but normal or increased in macrolytic anaemias.

Question 11

What is mean cell haemoglobin concentration (MCHC)?

When is this count useful?

Answer 11

• Mean concentration of Hb in RBC’s (Hb/MCV x RCC)

- Laboratory identification of cold agglutinins - generally one of the least useful parameters.

Question 12

What is red cell distribution width (RDW)?

What is it used to assess?

Answer 12

• Variation in the size of RBC’s

- Used to assess cause of anaemia, increased in iron deficiency

Question 13

What is reticulocyte count a measurement of?

When is it increased/decreased?

Answer 13

• Measurement of the number of young erythrocytes (identified by its size + remaining RNA content)
• Increase in haemolytic anaemias, blood loss, response to EPO etc
• Decreased in haematinic deficiency or bone marrow failure

Question 14

Define the following terms in relation to RBC’s:

• Microcytic
• Macrocytic
• Hypochromic
• Hyperchromic

Answer 14

• Microcytic = small RBC (MCV)
• Macrocytic = large RBC (MCV)
• Hypochromic = pale, less Hb
• Hyperchromic = dense, more Hb in given volume

Question 15

Give a description of the following inclusions that can be found in erythrocytes:

1) Howell-Jolly bodies
2) Basophilic stippling
3) Pappenheimer bodies
4) Heinz bodies
5) Haemoglobin inclusions

Answer 15

1) DNA/nuclear fragments
2) RNA inclusions in cells
3) Iron inclusions in cells
4) Denatured Hb
5) also denatured Hb, look like golf ball cells

Question 16

What are the 5 differential parts of a WBC count?

Answer 16

Neutrophils, Eosinophils, Basophils, Lymphocytes, Monocytes,

Question 17

What is the most frequent aberrant parameter?

Answer 17

Platelets