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Home > Dr JB Lim's Corner > Is Beta-Thalassemia Minor a health hazard to an airline pilot?
Is Beta-Thalassemia Minor a health hazard to an airline pilot?
Flying - Dr JB Lim's Corner
Thursday, 06 December 2007 18:47

Hi Capt Lim,

I have Beta Thalassaemia Minor and am wondering if I am fit for a career as a commercial pilot with Singapore Airlines. Perhaps you may want to ask Dr Lim Ju Boo who has kindly offered to answer certain specific medical questions on your behalf.

Thank you.

Warmest regards,

James Tan

Hi James,
Dr JB Lim has written a very comprehensive and detailed reply to your query on Beta-Thalassaemia Minor. You can personally email to thank him for sharing his expertise on this subject. I am attaching his reply below.
So now, you can submit your application to Singapore Airlines and leave the decision to the discretion of the Company doctor.
KH Lim.

Dear Capt Lim,

Thank you for your enquiry on behalf of the visitor to your website visitor who wanted to know about the risk of taking up a career as an airline pilot when he ‘suffers’ (inherits) beta-thalassemia minor, a genetic blood disorder. Before I answer that, let me explain in as simple a language as possible, a little about what these groups of diseases are all about. Then we can decide for ourselves if this disorder is really a health problem, or a liability to an airline that employs him. Scientific logic will tell us whether this inherited blood disease is a hazard to flying. Please read on.

What is Thalassemia? 

Thalassaemia is not one disease, but a group of inherited (genetic) diseases of the blood in which there is a fault in the manufacture of red blood pigment called haemoglobin or Hb for short. Hb is the red pigment found in the erythrocytes or red blood corpuscles (RBC). This helps carry oxygen to the tissues. Hb is synthesized in the bone marrow, and is then integrated into the RBC. In patients with thalassaemia, the RBC produced become very fragile, and becomes easily broken up (haemolysed). This leads to a kind of anaemia called haemolytic anaemia. Many types of thalassemia have been recognized due to a defect in the haemoglobin synthesis.

The most common type of thalassemia is beta thalassemia minor. This is caused by a decreased in the production of a type of haemoglobin called Hb A. This haemoglobin is the most common type that is the main Hb fraction from birth to death. All haemoglobins have two parts – the iron part called heme, and the protein fraction called globin. The Hb of normal individuals has two pairs of globin or protein chains, namely the alpha and the beta chains. In thalassemia, the synthesis of either alpha or beta chains is reduced, causing the ratio between alpha and beta chains to be unbalanced. This affects the quality of the haemoglobin produced, and thus its ability to carry oxygen to the tissues. In short, the victim becomes anemic. In beta thalassemia, the defect is in the production of the beta chain. Abnormal haemoglobin production in this disorder originates from the inheritance of a defective genes, the most common is the gene responsible for the production of beta globins.

A defect in this leads to beta-thalassemia. If an individual inherits a defective gene for this particular disease, he or she is said to have acquired ‘beta-thalassemia minor’ or ‘thalassemia trait’ which is never severe. But if both parents have thalassemia traits, and each defective genes comes from each parent, the offspring will suffer from a much more severe condition called beta-thalassemia major. Statistically, if two persons with beta thalassemia minor marry, and have children, a quarter of their offsprings will develop beta-thalassemia major, one half will acquire the minor form, and the other quarter will have none of these.

Beta-thalassemia Major

Beta-thalassemia major is sometimes called Cooley’s anaemia, named after the American paediatrician Thomas Cooley who first described it in 1925. In Cooley’s anemia, a child born is homozygous (having the same genes) for beta thalassemia. This causes a marked deficiency in beta chain synthesis and the production of normal Hb A.

Thalasssemia major is therefore a very serious disease. Initially a baby born with thalassemia major does not seem to have any problem. The baby looks normal alright. The predominant Hb at birth is a foetal haemoglobin called Hb F, and this has two alpha chains similar to Hb A The two gamma chains is unlike the normal Hb A. Although it has no beta chain, the presence of foetal Hb protects the baby from the effects of thalassemia major. But within the first three to six months after birth, the baby begins to show signs of severe haemolytic anemia, which progressively becomes more and more severe. The infant fails to develop normally (medically termed as “failure to thrive”), and has frequent feeding problems due to lack of haemoglobin and oxygen. The infant becomes short of breath, becomes jaundiced, and he is easily fatigued. There is also enlargement of the spleen due to rapid destruction of the RBC within this organ. The child experiences frequent fevers, diarrhea and gastrointestinal problems. In order to compensate for the shortened life span of the RBC (RBC normal life span is about 90 days), the bone marrow – the site of erythropoiesis (production of RBC) greatly expands, and may grow abnormally. So does the enlargement of the skull. Normal growth is arrested, and the child dies in early childhood if not treated with regular blood transfusion. Although blood transfusion will allow the child to grow normally, this also has its own problem.

The problem arises mainly in iron deposits into the internal organs, muscles, liver, heart etc. They eventually become overloaded with iron – a condition known as haemosiderosis which can lead to cirrhosis of the liver. Cirrhosis is a condition in which the liver becomes leathery and non-functioning. It may also lead to hepatoma (primary cancer of the liver). The iron deposit may also affect the heart, causing damage to the myocardium (heart muscles). Chelating compounds may be given to reduce the iron overload. An alternative route is to remove the spleen (splenectomy) if too much RBC are destroyed there, and if the spleen is enlarged. A bone marrow transplant is yet another option to consider. In contrast, those with beta thalassemia minor lead normal life.

An infant will grow up to be an adult, and can take up almost any occupation or profession he likes, provided (maybe) it is not so strenuous and oxygen-demanding, bearing in mind that the affected person has mild anaemia. Besides mild anaemia, and an asymptomatic presentation (no symptom), almost none of the complications experienced in the more severe beta-thalassemia major is featured in the minor form. All the person experiences is slight anaemia with no symptom. This anaemia is not different from the simple iron (nutritional) deficiency anaemia found in most menstruating young females. Mild anaemia in thalassemia traits does not require any treatment. It does not disrupt normal life, interfere with job, or occupation. The affected person merely shows a ‘trait’ or ‘a tendency’ towards certain characteristic features of the disease. Alpha-thalassemia:
The incidence of alpha-thalassemia is fortunately very much less common than the beta type. Here there is a severe reduction of the alpha globins. The lack of haemoglobin is just not compatible with life, and the infant dies within hours of birth. There is no question of the infant growing up to be an adult and wanting to be an airline pilot or hold any profession or job.


The diagnosis for any form of thalassemia is haematological (blood) profiling (blood tests), but for more differential diagnosis (diagnostic-specific), a haemoglobin analysis will differential the type of thalassemia by looking at the pattern of the globins fractions separated by electrophoresis in the laboratory.
Racial Origin and Geographical Distribution

Thalassemia is a disorder very common among races and in families originating in the Mediterranean region, South East Asia and in the Middle East. Hence it is not a surprise your enquirer is among those affected in this region of the world. Additionally, beta-thalassemia is the most common type throughout these geographical areas.
Oxygen Tension and Anemia
On the question whether or not this inherited disorder will affect his career as a pilot with SIA, or with any airlines, the chances it should not. Why should it be? The anemia and the trait are so mild. Reason this out. We expect the barometric pressure in the cabins of all airplanes to be normal or near normal. This implies the partial oxygen pressure in the cabins about 20.9 % which is the same as that at sea level. The normal atmospheric pressure at sea-level is 760 mm Hg and the oxygen saturation of the blood (haemoglobin) is about 96-98 %. If we look at the data on the oxyhaemoglobin dissociation curve – the curve that shows the ability of the haemoglobin to combine with oxygen under different (partial) pressures we can see the amount of haemoglobin being saturated with oxygen at different partial pressures. Let us translate these data in a mock-up scenario inside an aircraft that suddenly loses pressure.

What happens? First of all, there is always a contingency for an oxygen mask been dropped for everybody – for the passengers, flight attendants and pilots as well. Second, the physiological effects of an ‘oxygen want’ (hypoxia) applies for everybody – whether or not he is anemic, or has thalassemia. The physiological effects are the same, including for normal pilots without thalassemia. The effects will greatly vary from the amount of oxygen tension in the cabin, and the altitude of the aircraft during the pressure loss. But I believe the incidence of the cabin suddenly losing its pressure  is very rare indeed, unless there is a blast on board to allow all the pressurized air to escape.I am sure Capt Lim will concur with me that this rarely happens. So that sort of risk may be discounted. As I said, in an emergency, the effects of hypoxia applied to everybody even to those with normal haemoglobin levels. Back to the oxyhaemoglobin dissociation curve, and the effects expected, when the oxygen partial pressure drops to 19 % compared to 20.9 % at sea level, there are some physiological effects which are hardly noticeable. At 16 % (581 mm Hg) when the haemoglobin blood saturation drops to 92 %, impaired thinking, attention and reduced coordination may be visible. At 14 % oxygen level (523 mm Hg), when the oxygen blood saturation drops further to 90 % everybody, including a pilot with normal haemoglobin levels, and are not anemic, will suffer abnormal fatigue upon exertion, becomes emotionally upset, has faulty judgment and poor coordination.

When the partial oxygen tension reaches 12.5 % (450 mm Hg) the blood oxygen saturation will reach a critical 83 % level where a pilot without an oxygen mask to deliver oxygen under pressure, will experience very poor judgment, and coordination, He will experience difficulty in breathing (dyspnoea), his heart rate goes up (tachycardia) - a compensatory response, altered vision, nausea and vomiting. He will be unable to respond to any emergency. There is a shorten period of ‘useful consciousness’, the period the casualty can remain conscious to be useful to others, such as helpful to another victim of hypoxia, say a child who is more adapted to stay conscious for a longer time.Should the cabin pressure dropped further, so much so that the oxygen partial pressure is less than 10 % (equated to less than 387 mm of mercury), the blood Hb saturation will be < (less than) 70 %. In such event, there will convulsion, loss of consciousness and death. Given these emergency medical scenarios of oxygen want and deprivation, we may ask if such risk does actually happen in practice, let alone every day in an aircraft ? Obviously no. All modern aircrafts are fitted with emergency contingencies like having an oxygen demand system on board, and the ability of the pilot to lower the altitude immediately. I am not a pilot, but I am sure Capt KH Lim will agree with me on this point. Safety and preventive measures are all part of the features of a modern passenger aircraft. These scenarios very, very, rarely happen to the pilot or the passengers.

Emergency Situations

Even if such a rare and unusual emergency occurs, the physiological effects will be the same for everybody, whether or not he is the victim of anemia, or has traits of beta-thalassemia minor. One would expect an anemic individual to be worse off in sudden oxygen-deprived conditions. This, I suspect is what most people with a little scientific-medical background would reason out, and would expect. On the contrary, it may be just the opposite. An individual who chronically suffers from anemia, is more likely to be more adaptable to lower oxygen tension conditions. First of all, because of his chronically reduced oxygen-carrying capacity to deliver adequate oxygen to the tissues, his body will trigger feedback / compensatory mechanisms to override this. His bones and skull are larger to produce more bone marrow. His erythropoietic turnover is much more enhanced. There is also a much greater RBC count in the blood, and the RBC size is also much larger (shown by an increased number of immature megaloblasts in circulation).

In sufferers of thalassemia, the spleen may also be enlarged (splenomegaly) due to destruction of RBC. But at the same time, its holding capacity is also larger than normal to contain extra amounts of undestroyed RBC and blood kept on hold. In a hypoxic emergency, the spleen is bound to contract to discharge all those extra blood and RBC into the circulation to meet that emergency. The body of a pilot who has no blood abnormality, the body physiologically ‘takes for granted’. His body may not be as well prepared as one whose body suffers from some deficiency. A deficient body is more well adapted to changes than one which is considered ‘normal’. In short, a blind man compensate his disability in sight by an increased sense of hearing, and the sensitivity of his touch and feelings. The body adjusts to all these changes all the time.

Menstruating Young Women and Anaemia

But as I already said, I do not think the cabin pressure in a good aircraft is chronically below the normal atmospheric pressure. While should it be when the pilot can control the pressure, unless I am wrong, and Capt Lim can be kind enough to correct me. Even if the pressure drops a little, it does not make any difference to the mental and physical performance of the pilot. I have already listed the various effects above. The condition of a beta-thalassemia minor ‘patient’ is exactly like a young women who is slightly anemic due to the normal monthly menstrual loss of iron. But she is piloting a plane.

Does that make any difference? You can answer this yourself by analyzing the lengthy explanation I have given about the role of haemoglobin in this inherited disorder, and a young women whose Hb is slightly below the norm, but she is running about doing all sorts of job.   Rest assured nothing will happen to anybody whether he is a passenger or a pilot, and that he / she is only anemic. If it is dangerous to fly if one is anemic, then all females of menstruating age who are normally anemic, should not be flying about at all in an airplane. That would be hazardous to career and health would it be? That includes all the air stewardess who must all be grounded for such irrational ‘medical’ reasons. Does that make sense? Of course not. Anemic females are flying all over this globe – millions of them every year. Nothing happens to them.

Employers Making Demands

This is as far as the medical logic and explanation is concerned. Notwithstanding what I said, every airline will have their own individual guidelines on conditions to accept pilots for employment. There is no set standards in the medical condition required. Each employer / airline will have their own criteria to recruit pilots for employment to meet their own requirements and needs. Each will have their own and individual criteria and guidelines. Malaysia Airlines may have one set, Singapore Airlines another set, British Airways another set, Quantas yet another, and so on. No two employer / company have the same rules and requirements. Each caters for their own needs. Some are more lenient, others are more demanding.
However, there are certain medical conditions which must be met internationally for all pilots. For example, a pilot must not have a history of mental disease, or has uncontrollable high blood pressure, or has a history of epileptic fits or psychomotor seizures. Imagine a pilot prone to epileptic seizure every now and then. How would you like to be in his aircraft especially during the crucial take off and landing. Personally, if I know the pilot who is going to fly me has a history of epilepsy or is prone to heart attack, or CVA (cerebral vascular accident or stroke) and who is in the cockpit, I would immediately take another flight. I just don’t want to be in that plane. Similarly, one of the international medical requirements for a pilot is that he must have good eye sight, and he must not be blind or deaf. Imagine the pilot who cannot see the runway, or he is colour blind, and cannot differentiate the coloured signal lights, let alone he is blind, and cannot even see the airport or his plane. Imagine an airline company employing a pilot who also deaf, and cannot hear anything on his earphone during his radio communications with the control tower. It is dreadful even to think about it, let alone sit in his plane for ‘safety’. Which airline will employ such a pilot? Such requirements are mandatory, and overrides all other medical criteria demanded by an employer. Capt Lim is in a better position to tell you all the stringent requirements he has to undergo. I think such medical requirements are very obvious, and they apply internationally.  

Other Minor Demands
What I am trying to say here is that, there are minor or other unrelated health conditions a pilot may suffer which have no relevance to his occupation. For instance, a pilot may suffer from lactose intolerance. This condition is not a threat to his flying. All he needs is just to avoid drinking cow’s milk, unless he doesn’t mind the inconvenience of going to the toilet every hour or so for his diarrhea. The picture may be slightly different if he has a history of recurrent bronchial status asthma (a very severe and prolonged form of asthmatic attack). That will be terrible to have such a pilot on board. A pilot who is chronically tired and sleepy all the time, or is irrational in his thinking, and is unable to make sound judgment, is just not medically fit to be on the job. Similarly, no airline will employ a pilot who hallucinates or ‘hear voices’ (other than sound technical language through his ear-phones with the control tower). Certain of these medical / health requirements are quite mandatory and standard procedure everywhere. Other than that, they may want you to declare other illnesses under “others”. Every airline / employer may like to add these at their own discretion. Some employer are sticky, others are more flexible. It actually depends on each airline.However, until today, I have not come across any medical examination forms for employment purposes which listed ‘beta-thalassemia minor’ as one of the disorders to look out. It may be relevant for marriage and parenthood counseling, but not for piloting a plane, as far as I know.

Every medical examination for employment purposes are different. There is no such ‘standard’ forms where the examining physician needs to fill up. It is up to the discretion of the medical examiner and the recruitment board on what to include. Some may like to include ‘thalassemia’ in the employment form for whatever their reasons. It is up to them. No one can stop or argue with them. It is the employers’ right. Employees either accepts the agreement or leave it, even if the demands and reason(s) have no relevance to their work. Each company constructs their own forms in whatever way they seem fit. I have seen forms which are so simple, just 2-3 tests, while others, demand a very long (and unnecessary) conditions to look for. Some are as short as just looking for high sugars or high cholesterol in the blood with any other clinical examination. Some companies, especially insurance companies have a team of medical advisers sitting in their acceptance board. Some just get a few doctors from outside on a part time ad hoc basis. It is their absolute right how they like to choose their conditions – health or otherwise. But so far, I have not seen ‘thalassemia’ as part of a normal medical examination in any examination forms, for work or for play. The only exception I have seen were in the research forms which I shall explain below this paragraph.

My Professional Experience

I was then working in the various Divisions of Nutrition, Clinical Research, Community Medicine, Behavioural Sciences, and Rural Health for 25 years (1969 -1964) at the Institute for Medical Research (IMR), Ministry of Health. During my work in these various departments, we went out conducting health surveys among hundreds of thousands of people in various parts of the country. We examined them, we take various measurements, we take their blood, urine and stool, we questioned them, we take their history, we examined their diet, and we recorded all the information about their health status – hundreds of thousands of people were involved in every Government health projects. In such massive exercise for health studies, we always device our own medical / health and examination forms and requirements. . We invent and device examination and survey forms ourselves according to our own needs.There is no such thing as a common and standard medical exam form to fill up. If we suspect there is a particular health problem in that area, and that can affect their well-being, or national productivity, we just include them in our forms. Others, we just throw them away. There are tens of hundreds of diseases a human being can suffer from, and it is just not possible to examine and screen every one of them for every person. It would be sheer madness to do that. That is what we do from our side, working together as a team of medical and health experts for the Government.

The Scientist-Physicians I Knew

On the other hand, I also knew a couple who was also working in the same Medical Institute as myself. This husband & wife team was an internationally well-known physician and haematologist who was working in the area of thalassemia. I knew them as we were colleagues, but working in a separate department at the IMR. The couple, especially the wife, was an internationally renown Indonesian Chinese Consultant Haematologist (a medical doctor who specializes in blood disorders). They have published a lots of research papers on thalassemia, and naturally their interest is only on thalassemia. When she conducted her own medical examination on a population, she was only interested in screening for thalassemia, and threw away all the other types of medical examination or attend to the health needs in other areas in the population. They were not interested in the rest of the other medical problems at all. They were super-specialists with an international reputation, specializing only on one type of disease. The couple has since died. It was the husband-wife right to determine what was more important to them as they were such eminently renown researcher-scientist and physicians put together. Similarly, within our own departments at IMR, we have our own team of medical expertise and scientists. We create our own forms, and requirements on what health conditions to look for. They were left entirely to our discretion, and no outside doctor or researcher had the right to comment or interfere with that.. No one can challenge what we needed to do.

The Rights of An Employer

Similarly, no one can challenge what Singapore Airlines or any airline wants in their pilots recruitment drive. Even if beta-thalassemia minor has nothing to do with flying, but if they insist on including it on some ill advice by their company’s doctor who thinks it should be included, then it is their right for whatever their reasons. No one can say yes or no. Normally in my work experience at the IMR, a team of us – all medical experts, research scientists, and other health-care professionals employed by the Government will work together as a team. We discussed problems together, and we designed our own requirements. We would decide on what to include, and what to throw out. We know the problem better, and we made the decision ourselves. No one can interfere. So does the airline as an employer. It is their right whether or not to include beta-thalassemia as a health hazard to their company. Obviously this would not be the case with beta-thalassemia major where an untreated child life span can only reach up to childhood, let alone grow up to adult stage where he can hope to be a pilot. In the case of alpha-thalassemia,  it is even worse as I have pointed out. The victim’s life-span is only hours away, or just days after birth. There is no question of him becoming a pilot, or undergo any medical examination at the whims and fancy of the employer. The victim would be lucky to live beyond neo-natal age (after one year). But in the case of beta-thalassemia minor, a normal life-span, normal life, and almost any occupation can be expected. It is absolutely not a problem at all..

No Problem After All
So what’s the problem dear Captain? Ask your enquirer to go ahead and apply for a job as a pilot with Singapore Airlines or with any airline. But as I said, the ultimate decision lies with the company, and not with your friend’s condition, which in my opinion is no health threat at all. I hope I have been of help to your website visitor, Captain Lim. Please do feel free to contact me again if you need further opinion or information  

Yours sincerely,

JB Lim  
BSc, MD, PG Dip Nutr, MSc, PhD Med (Lond)
FRSH (Lond), FRSMed (Lond), DSc (Int Med)


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