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problem, its cause and natural history. The overriding concern is that the blood must carry sufficient
oxygen to satisfy metabolic requirements at rest, during exertion and anxiety, both at ground level and at
altitude.
ANAEMIA
Anaemia is a condition in which the haemoglobin concentration in the blood is below a defined level,
generally 13 g/L for men and 12 g/L for women, resulting in a reduced oxygen-carrying capacity of red
blood cells. About half of all cases of anaemia can be attributed to iron deficiency; other common causes
include infections, such as malaria and schistosomiasis, and genetic factors, which result in thalassaemias
and sickle-cell disease. In its severe form, anaemia is associated with fatigue, weakness, dizziness and
drowsiness.
In those who fly, the reduced oxygen tension associated with altitude exacerbates the effects of anaemia.
Applicants whose haemoglobin is less than normal should be further investigated. The final assessment
would be dependent on the results of the investigation and the response to the treatment, if any. It is
difficult to specify a threshold value of haemoglobin below which certification can no longer be granted.
There is considerable variability of intolerance according to whether anaemia is chronic or acute as the
body can adapt to anaemia by increasing its production of haemoglobin F and 2,3-DPG1 which enhances
oxygen affinity.
Even so, those with a haemoglobin concentration below 10.5 to 11 g/L should be considered as not
meeting the standards. If the anaemia is caused by thalassaemia minor or any other haemoglobinopathic
trait, and the applicant has full functional capability and no history of crises, a fit assessment is usually
possible.
1 2,3-DPG: 2,3-diphosphoglycerate
ICAO Preliminary Unedited Version — November 2009 III-5-2
GLUCOSE-6-PHOSPHATE DEHYDROGENASE (G6PD) DEFICIENCY
G6PD deficiency is an X-linked recessive hereditary disease featuring non-immune haemolytic anaemia
in response to a number of causes. The classic reaction to consumption of broad beans (Vicia faba) has
led to the commonly used term “favism”, derived from the Italian name of the broad bean (fava).
Almost all patients are male, although some female carriers can be clinically affected. The most common
clinical symptoms are chronic anaemia due to a continuous haemolytic process and haemolytic crises in
response to certain medicines and certain foods, most notably broad beans. Also infections and diabetic
ketoacidosis may give rise to a crisis, and very severe crises can cause acute renal failure. Many
medicines have been linked to G6PD, in particular primaquine, sulphonamides, glibenclamide and nitrofurantoin.
In some parts of the world, a screening test for G6PD is part of the initial medical examination for
certification. However, G6PD deficiency is not necessarily a bar to certification provided the
haemoglobin level is stable and the pilot is well aware of what foods and medicine should be avoided.
ERYTHROCYTOSIS
Applicants with higher than normal haemoglobin should be further investigated.
Traditionally, the term ‘polycythaemia’ has been used about several disorders with an increase in
circulating red blood cells but ‘erythrocytosis’ is a better and more correct term. Applicants with a
persistently raised venous haematocrit (>0.52 males, >0.48 females for > 2 months) should be
investigated by measurement of their red cell mass (RCM). Normally RCM is expressed as mean
predicted value based on surface area. The diagnosis of absolute erythrocytosis is made when an
individual’s measured RCM is more than 25 per cent above their mean predicted value. The term ‘relative
erythrocytosis’, where RCM is within the normal range and plasma volume is reduced, should be reserved
for states of dehydration. ‘Apparent erythrocytosis’ is the term used for those individuals who have a
raised venous haematocrit but with a red cell mass within the reference range.
It is important to distinguish between primary erythrocytosis which is a myeloproliferative disease and
secondary erythrocytosis due to other conditions.
People living at high altitude (e.g. Mexico City) must be expected to have secondary erythrocytosis with
an elevated haemoglobin and haematocrit. In cases of secondary erythrocytosis due to lung disease or
cyanotic heart conditions, the underlying pathology would have a greater bearing on the final assessment
than the erythrocytosis per se.
Primary erythrocytosis, in particular polycythaemia rubra vera, should normally be considered
disqualifying owing to its propensity to thromboembolic complications, cerebro-vascular accidents and
its rapid, unpredictable progression. Depending on the results of a specialist’s report and response to
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Manual of Civil Aviation Medicine 1(144)
