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Amongst the haemoglobinopathies, one such condition found predominantly and in varying proportions
in Africa, in the Mediterranean littoral and also in southern India is sickle-cell disease. Collectively
known under this name are the homozygous state, sickle-cell anaemia, and heterozygous combinations of
the sickle-cell gene with genes for other abnormal haemoglobin and for thalassaemia. The heterozygous
combination of normal haemoglobin with sickle-cell haemoglobin is known as sickle-cell trait (AS)
which must not be confused with sickle-cell disease.
The single most important qualitative haemoglobinopathy is sickle-cell anaemia. The most prevalent
quantitative haemoglobinopathy is ∃-thalassaemia, which has a world-wide distribution.
Sickling conditions
Sickling conditions are those in which red cells containing Hb S undergo the sickling deformation on
deoxygenation. Hb S transports oxygen normally, and is harmless except for the effects produced by
sickling of the erythrocytes. The clinical manifestations are the result of intravascular sickling, and if this
phenomenon is prevented there is no evidence of disease. The occurrence of intravascular sickling
depends on the degree of deoxygenation of the haemoglobin, which is largely determined by the oxygen
tension and pH in the various local areas of the vascular system; the tendency to sickling is also affected
by the concentration of Hb S in the red cells, and by the presence of other haemoglobins that may interact
with Hb S. The sickling of red cells in the circulating blood has two major pathological effects:
a) The deformed and elongated erythrocytes are rigid and their cell membrane is damaged; as a result,
the sickled red cells are removed rapidly from the circulation by the reticuloendothelial system,
producing haemolytic anaemia.
b) The misshapen cells lack normal plasticity; they block small blood vessels, impairing blood flow
and the delivery of oxygen, so that ischaemia and infarctions may occur in the tissue served by the
occluded vessels. Vascular occlusions tend to occur in those areas in which conditions of blood
flow and low oxygen tension enhance the tendency of erythrocytes to sickle, notably in the spleen
and bone marrow, although any vascular area may be involved. Local pain, functional impairment,
and other clinical manifestations are attributable to the vascular blockade.
3 von Willebrand’s disease: a congenital bleeding disorder, caused by deficiency of von Willebrand’s factor (factor
VIII-related antigen) and characterized by increased bleeding after trauma and surgery. Called also
angiohaemophilia and pseudohaemophilia. After Erik von Willebrand, Finnish physician (1870-1949).
ICAO Preliminary Unedited Version — November 2009 III-5-5
Sickle-cell disease
Splenic infarctions have repeatedly been reported occurring in flight due to sickling of red blood cells.
Sickle-cell disease, which includes sickle-cell anaemia (SS), sickle-cell haemoglobin C disease (SC),
sickle-cell thalassaemia (STh), sickle-cell haemoglobin D disease (SD) and other pathological genotypes
involving haemoglobin S with other genetic variants, is disqualifying for flying.
Sickle-cell trait
A clear distinction must be made between sickle-cell disease (SS, SC, SD and STh) and sickle-cell trait
(AS). The diagnosis of sickle-cell trait should be based on the following findings (including results from
sickling tests): the patient should not be anaemic, and should have normal red cell morphology, normal
levels of haemoglobin F, and a haemoglobin electrophoretic pattern of haemoglobins A and S in which A
predominates (i.e. the concentration of Hb S is less than 45 per cent of total haemoglobin).
There is no reason to impose any limitations whatsoever on applicants with sickle-cell trait.
REFERENCES
British Committee for Standards in Haematology: Guidelines for the diagnosis, investigation and
management of polycythaemia/erythrocytosis, by the General Haematology Task Force (2005), retrieved
from www.bcshguidelines.com/pdf/polycythaemia.pdf
World Health Organization, Report by the Secretariat, EB 118/5: Thalassaemia and other
haemoglobinopathies. Geneva, 2006
————————
ICAO Preliminary Unedited Version — November 2009
PART III
Chapter 6. URINARY SYSTEM
Page
Introduction .................................................................................. III-6-1
Renal Calculus Disease ................................................................ III-6-2
Overview ................................................................................. III-6-2
Clinical features ....................................................................... III-6-2
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Manual of Civil Aviation Medicine 1(146)
