From anemia to zoonosis, the benefits of medical screening need to outweigh the drawbacks
DRUG BUST by Alan Cassels
(zo•on•o•sis) n. a disease passed from animals to humans.
The best and most useful medical screening takes people with no symptoms and puts them through a safe and simple test that can accurately locate a disease in an early enough stage to stop it from hurting or killing them. After all, that’s why you screen people – to prevent them from being hurt. Any medical screening program intended for entire populations of healthy people needs to be studied well to ensure the benefits outweigh the harms. Unfortunately, few medical screening tests fill this bill.
But some do. How about the screening of blood?
If you are a blood donor in Canada, as I am, you know if you want to donate, you will be put through a rigorous, demanding and sometimes embarrassing medical screening program that drills down into the very core of what it means to be perfectly healthy. Don’t get me wrong; I’m not against this. Lax blood-screening protocols in the past led to thousands getting tainted blood – a scandal that still resonates in the medical community.
The good folks at Canadian Blood Service screen you for almost everything: your past, where you’ve lived, which diseases or medical procedures you’ve had, who you’ve had sex with and so on. They also screen your current state of health and the nurse will check your temperature, blood pressure and pulse. Your donated pint of red stuff will be tested for seven different diseases, including hepatitis, HIV, West Nile virus, syphilis and others. They are extremely careful about the purity of the blood supply.
The screening procedures blood donors go through is like the flip-side of standard medical screening: instead of looking for something that might hurt you, blood donor screening is all about the health of your neighbour, the soul who receives your blood.
One aspect of this screening I find particularly fascinating is the test for low iron. Once the blood donor clinic has ascertained who you are, they poke your finger and squeeze a drop of blood into a little vial of blue liquid. If the drop of blood sinks like a stone, you’re OK. If not, you’ve probably got low iron. A machine has now replaced the blue vial, but if you’ve got low iron, you’ll be barred from donating and told to go see your doctor.
I was totally surprised when this happened to me a few years ago. Here I was, feeling all hale and hearty, with none of the symptoms of low iron, such as tiredness, shortness of breath, etc. A quick trip to the lab determined my iron levels were borderline at 125 grams/litre and my doctor reassured me that, in the absence of symptoms of slow blood loss, which can sometimes go unnoticed, I didn’t need to worry.
Anemia is so common that about 15 percent of blood donors are turned away because of it. It can be caused by either not absorbing enough iron into your blood or excreting blood, possibly the result of stomach ulcers, polyps and even colon cancer. Blood loss can be very gradual and you may not notice it until you’ve had your hemoglobin checked.
Is ‘screening’ for iron deficiency a useful medical test? Obviously, if you have any symptoms whatsoever your doctor will send you for more sensitive lab work to see if iron deficiency is suspected. But what about the general population? Should we all get checked out even if we feel well?
There may be some things in favour of population testing for low iron, but, in practice, it doesn’t happen in the context of a big program. Doctors generally manage it on their own, especially in patients with symptoms. Measuring hemoglobin levels is one of a few rare screening tests that can actually leave little doubt as to what is being measured.
In some parts of the world, anemia constitutes a major public health problem. As much as half the population of some countries might be suffering from anemia. Iron deficiency anemia was part of a discussion by a World Health Organization (WHO) study group in 1958 and it was only after that meeting that the WHO adopted criteria for blood hemoglobin levels below which a person is likely to be suffering from anemia.
According to the WHO, women of childbearing age screened for anemia have the highest incidence of the condition. Women are more likely to be anemic than men because of the iron loss that happens through menstruation. In most countries, routine maternity care includes ‘screening’ the blood of pregnant women to make sure iron deficiency, which could harm their developing fetus, is not present.
Beyond menstruation, however, there are other ways to become anemic. Blood diseases as well as other diseases, particularly those caused by parasites, are often the culprits.
The WHO’s 1968 publication Principles and Practices of Screening for Disease created what is likely a seminal document recognizing the many problems with screening. It concluded anemia is “probably one of the more acceptable conditions for screening under present circumstances; it is highly prevalent, can be sufficiently accurately detected and, when due to primary iron deficiency, responds excellently to treatment.”
The level of iron in your blood is a marker for disease and certainly in the developing world there are a whole range of potential causes.
But back to the developed world.
My research into medical screening over the last year has led me to conclude the “test early, test often” axiom is only justified for a few worthwhile, well-studied and valuable screening programs while most of those programs are harmful and prevent few deaths.
Which leads me to the “what if?” question: What if, instead of a world where screening harms people inadvertently while searching for more and more elusive diseases, we had something different? What if we used very simple technology to find the markers of deadly diseases that could be intervened at an early stage, before they went on to hurt people – better yet, if the diseases in question affected a huge swath of humanity suffering untold (but highly preventable) miseries?
This brings us to zoonoses, which are diseases passed from animals to humans. In Canada, you can easily pick up parasites like roundworm or hookworm from a pet, but other sexy and rarer zoonotic diseases such as monkeypox, anthrax and rabies get much more attention. In the western world, we don’t screen for zoonotic diseases, but shouldn’t we be doing it in the developing world?
The WHO’s stance is “iron deficiency affects more people than any other condition, constituting a public health condition of epidemic proportions.” Further, “the numbers are staggering: 2 billion people – over 30% of the world’s population – are anemic, many due to iron deficiency, and in resource-poor areas, this is frequently exacerbated by infectious diseases.”
Other than HIV and tuberculosis, the major diseases afflicting mankind and the ones with the greatest death toll are zoonotic diseases. Malaria (transmitted by mosquitoes), hookworm (a worm that lives in the intestine and causes anemia) and schistosomiasis (a parasite carried by freshwater snails) afflict literally billions of people around the world, causing high levels of anemia in many places on the globe.
Iron deficiency may be the true silent killer, exacting more of a toll in terms of illness, premature death and wasted human energy than anything else we know. Millions of people are home to parasites, literally sucking their blood. They become anemic and struggle to consume enough protein-rich food, functioning at only a fraction of their normal energy level. And guess what? The poorest and the least educated among us are most vulnerable to iron deficiency.
Would more screening help? In the developing world, almost more of anything would help, but, at the very least, systematically educating the population about iron deficiency would be simple. We know the tests for iron deficiency are quick and cheap and solutions revolve around controlling infection and improving nutrition.
Iron deficiency literally sucks the energy and vitality out of development.
Forty years ago, the famous Dr. Julian Tudor Hart coined the term the “Inverse Care Law,” which, in its elegant simplicity, states, “the availability of good medical care tends to vary inversely with the need for it in the population served.” Which is to say, the more urgent our medical needs are, the less likely they are to be met.
I propose the ‘Inverse Screening Law’ is alive and well too, where huge sums of money are spent on useless and harmful population screening while almost nothing is spent on screening and treating anemia, a condition suffered by billions in our global community.
Alan Cassels is a drug policy researcher at the University of Victoria. Read more of what he’s writing about atwww.alancassels.com