Haemoglobinopathies

Question 1

How is the solubility test used to diagnose sickle cell anaemia?

Answer 1

Predominantly used in the UK.

Detect Hb S in concentrations as low as 20%, in some cases even down to 8%.

HbAS and HbSS precipitate in low O2 tension due to polymerisation.

Haemolysis ESI mixed with a powerful reducing agent.

Normal Hb remains clear, whereas HbSS and HbAS will turn sample cloudy.

Question 2

What are the follow up tests for SCA?

Answer 2

Electrophoresis:
Variant haemoglobins can be differentiated from each other by electrophoresis on cellulose acetate paper.
A = normal adult
SS = sickle cell anaemia patient
AS = patient with sickle cell trait
AC =patient with haemoglobin C trait

HPLC:
HPLC is used to detect, provisionally identify and quantify the different variations of haemoglobin (S, A2 and F) in order to diagnose sickle cell anaemia, relying on the different ionic properties of different haemoglobins. This accurate quantification of Hb A2 can also suitably diagnose the B-thalassaemia trait.

Isoelectric focussing:
- Each variation of Hb has a different migration time.
- It gives good separation of Hb F from Hb A and clinically significant
variant haemoglobins (S, C, D-Punjab, E and O-Arab).
- However, this has NOT been validated for Hb A2 quantification.
- Identification is only provisional and a second line method
should be used for further analysis.

SDEX