Test Background The sickle cell test is available as part of haemoglobinopathy screening.
Hb S is an abnormal haemoglobin caused by a single point substitution of valine for glutamic acid in position 6 of the β-globin chain. The homozygous state, sickle cell anaemia, is characterised by the formation of sickle red cells and moderate to severe anaemia. Sickle cell trait, the heterozygous state, is very common, with no associated haematological abnormalities. In vivo sickling occurs only at very high altitudes and at low oxygen pressures.
The sickle solubility screen provides a quick and reliable method of detecting this abnormal haemoglobin. The test is based on the principle that Hb S, in its reduced state, is less soluble in concentrated phosphate buffers than nearly all other haemoglobins (the exceptions being the rare Hb C Harlem and Hb C Georgetown).
A sickle screen is required for patients in high risk groups, especially prior to a general anaesthetic and if there is no prior haemoglobin electrophoresis result with imminent surgery expected. If surgery is planned for more than one week away, haemoglobin electrophoresis results should be performed instead of a sickle screen.
Please note: unlike the haemoglobin electrophoresis, the sickle screen test does not differentiate between the sickle cell trait and the sickle cell anaemia state (or variants of this). All samples with requests for sickle screening tests will be followed up with haemoglobin electrophoresis and additional haemoglobin studies if deemed appropriate.
Clinical Indications Sickle screens are performed prior to emergency surgery or where full haemoglobinopathy testing will not be available prior to anaesthesia.
Sample Required 4 mL EDTA (lavender top) adults
0.5 mL EDTA (lavender top) paediatrics
Sample Volume 0.5 mL adult tube
0.2 mL paediatric tube