BOF: General (Haemoglobinopathy)

Which ONE of the following statements regarding the sickle solubility is FALSE?

a) Can produce false positive results in anaemic patients

b) Can produce false positive results in patients with high plasma protein levels

c) Is a clinically useful test in isolation before emergency anaesthesia

d) Is almost always positive in cases of sickle cell trait

e) Rules out homozygous sickle cell disease if negative at birth

Answer:

e) Rules out homozygous sickle cell disease if negative at birth

Explanation:

The sickle solubility test is usually not indicated before 6 months of age, as negative results may be misleading with the persistence of HbF. In the context of emergency anaesthesia or surgery, a negative sickle solubility test may well be clinically useful, as it indicates that any HbS is present at a very low level. Assays for sickle solubility routinely detect HbS concentrations of 20% or lower, and so is almost always positive in cases of sickle cell trait. Anaemic samples can produce false positive results as larger volumes of blood are assayed; such samples should be concentrated or washed in the laboratory.

Reference:

Ryan, K., Bain, B.J., Worthington, D., James, J., Plews, D., Mason, A., Roper, D., Rees, D.C., de la Salle, B. & Streetly, A. (2010). Significant haemoglobinopathies: guidelines for screening and diagnosis. British Journal of Haematology, 149, 35–49.