Practical 2: Exam Notes

Question 1

What does a white blood cell count determine

Answer 1

The concentration of white blood cells in the patient’s blood

Question 2

What does a differential wbc count determine

Answer 2

The percentage of each of the five types of mature wbcs

Question 3

Why might a WBC count be elevated

Answer 3

Infection

Allergy

Systemic illness

Inflammation

Tissue injury

Leukaemia

Question 4

Why might a WBC count be low

Answer 4

Viral infections

Immunodeficiency states

Bone marrow failure

Chemotherapy

Leukaemia

Question 5

What is a blood film

Answer 5

A monolayer of blood cells distributed with minimum distortion on a glass slide

Question 6

What stain is used for blood films?

Answer 6

Wright Stain (Romanowsky stain)

Question 7

What is the principle behind the Wright stain

Answer 7

its a polychromatic stain consisting of buffered solutions of methylene blue and eosin

Question 8

Define anisocytosis

Answer 8

Variation in rbc size

Question 9

Define poikilocytosis

Answer 9

Variation in rbc shape

Question 10

What is a Howell-Jolly body

Answer 10

DNA remnant

Question 11

What is basophilic stippling

Answer 11

Denatured RNA

Question 12

What are siderotic granules

Answer 12

Granules containing iron

Question 13

What are Heinz bodies

Answer 13

Oxidised denatured haemoglobin

Question 14

Define ESR
(2)

Answer 14

The time taken for RBCs to settle out of the plasma in an anticoagulated blood sample which is left standing upright

The rbcs settle out of plasma under the influence of gravity when allowed to stand for a period of time

Question 15

What are schistocytes and when might you see them?

Answer 15

Fragments of rbcs

Seen in thalassaemia or megaloblastic anaemia

Question 16

In what diseases would ESR be used as a means of monitoring the condition?
(3)

Answer 16

Systemic lupus erythematosus

Temporal arthritis

Systemic vasculitis

Question 17

How does disease affect ESR?
(2)

Answer 17

Normal rbcs are negatively charged which keeps them separated from each other

In disease this negative charge is reduced -> consequent formation of rouleaux which will fall quicker

Question 18

What is the basis of mononucleosis detection?

Answer 18

Tests are based on the detection of heterophile antibodies

Question 19

What are heterophile antibodies?

Answer 19

Antibodies produced against poorly defined antigens and that they are generally “weak” antibodies with broad specificity for carb antigens that can react with molecules found on the surface of nonhuman erythrocytes

They may be the consequence of polyclonal B-cell infection by EBV

Question 20

What stain do we use for our WCC and what is the principle behind this stain?
(4)

Answer 20

Turk’s solution

Turks solution contains a stain (gentian violet) and 6% acetic acid

Gentian blue stains the wbcs

Red cells are destroyed by the hypotonic solution plus acetic acid

Question 21

How do you use the haemocytometer?
(4)

Answer 21

Count the wbcs you see in the four outer corners of the haemocytometer

Add them all together to give you N

(N x 20)/ 0.4 ul = ul

(N x 20 x 10^6) / (0.4) = L