Deciding What is Normal and Interpreting Blood Count

Question 1

What is a reference range?

Answer 1

a range derived from a carefully defined reference population.

Derivation:
- These are derived by collecting samples from healthy volunteers with defined characteristics.

• The volunteers are then analysed using the SAME instruments and techniques that will be used for patient samples – to ensure variables are kept to a minimum

Question 2

What are the units for the following: 
WBC
RBC
Hb
MCV
MCH
MCHC
Platelets

Answer 2

WBC - x10^9/L

RBC - x10^12/L

Hb - g/L

MCV (mean cell volume) - fl (PCVX1000 / RBC)

MCH (mean cell haemoglobin) - pg (Hb/RBC)

MCHC (mean cell haemoglobin concentration) - g/l
platelets - x10^9/L (Hb/Hct)

*PCV = packed cell volume

HCT = haematocrit ratio

Question 3

What’s the difference between MCH and MCHC?

Answer 3

The MCH is the ABSOLUTE amount of Hb in an individual RBC.
- In micro/macrocytic anaemias, the MCH tends to parallel the MCV.

The MCHC is the CONCENTRATION of the Hb in the RBC – i.e. will change with the shrinkage or growth of the cell, while the MCH will not change

Question 4

How are MCV, MCH and MCHC measured?

Answer 4

MCV - total volume of RBCs in a sample divided by the total number of RBCs in a sample - PCV/RBC.
- Now determined indirectly by – light scattering OR interruption in an electrical field

MCH - Amount of Hb in a given volume of blood divided by the number of RBCs in the same volume - Hb/RBC

MCHC - Amount of Hb in a volume of blood divided by the proportion of sample represented by RBCs - Hb/PCV, Hb/Hct.

• Measured electronically, most accurately using light scattering.
• High MCHC could indicate irregularly contracted cells of spheroidal cells

Question 5

How do you interpret a blood count?

Answer 5

1. Is there leucocytosis or leucopenia?
   a. If so, why?
   b. Which cell line is abnormal? Any clinical history clues?
2. Is there anaemia?
   a. If so, is there any clues in the blood count?
   b. Are the cells large or small? Any clinical history clues?
3. Is there thrombocytosis or thrombocytopenia?
   a. If so, is there any clues in the blood count?
   b. Any clinical history clues?

Question 6

What is polycythaemia?

How can you evaluate it?

Answer 6

too many RBCs in circulation.

In polycythaemia, the Hb, RBC and Hct are ALL INCREASED compared with normal subjects of the same age/gender.

Evaluation:
- Clinical history & Physical examination – splenomegaly, abdominal mass or cyanosis could be relevant.

• Compare the above with the appropriate normal range.
• The Hb, RBC and Hct will all be higher in a neonate, lower in children than adults and lower in women than in men.

Question 7

What is pseudopolycythaemia?

Answer 7

the same symptoms of polycythaemia can be present but due to a decrease in plasma volume (so increase in concentration). I.E. burns draw plasma to the surface.

Causes:
- Blood doping – adding blood to your own – too much blood.

• Medical negligence – i.e. gave too much blood in a transfusion - Can then give venesections to remove excess blood.
• Erythropoietin: Physiological high levels of erythropoietin – increased blood cell production in response to hypoxia at altitude/ Illicit erythropoietin – inappropriate administration to artificially raise RBC count / Tumour erythropoietin – renal or ectopic tumour secretes erythropoietin.
• Abnormal function of bone marrow – inappropriate increased erythropoiesis WITHOUT erythropoietin - This is called polycythaemia vera – classed as a myeloproliferative neoplasm - This can lead to hyperviscous blood and vascular obstruction.

Question 8

What is the treatment of polycythaemia?

Answer 8

Blood removal – venesection

Drugs – for intrinsic bone marrow disease, drugs can reduce production of RBCs in bone marrow