Health Surveillance - Why & How.

Health Surveillance can be confronting for an organisation. There are a number of groups that offer it, and there are just as many opinions on what is required for your organisation to meet its legislated and ethical requirements.

Health surveillance is used to identify those at increased risk of developing an occupational health disorder,  and detect adverse health effects at an early stage so the worker may be protected from further injury, either by control of the process or by removal from exposure. Health surveillance is not a control measure in itself, though it is a very important component in assessing whether an organisation’s control measures are effective. 

There are specific chemical exposures that have legislated requirements for surveillance under Work Health and Safety laws throughout Australia. Most of these, and the recommended tests, are listed here. This is prescriptive and advises on the minimum requirements. The tests that are recommended are based on best practice .

How do you determine which tests are used as part of health surveillance? You use relevant and validated screening tests. And this is the important factor, the tests must be screening tests, not diagostic tests. What’s the difference? In simple terms:

  • Screening test - a test that is used to identify potential indicators of illness or disease
  • Diagnostic test - a test that is used to confirm the presence of disease.

In other words, a diagnostic test is used by a doctor to confirm what they already think is going on. If a person has retrosternal crushing chest pain and the doc is pretty sure its an AMI , they will get an ECG to see if there are ST segment changes that confirm the AMI. 

A screening test is a different animal. Its purpose is to see if there are changes in the individual’s body that could be due to the exposure in question. And there are important things to consider when you design a screening test. It needs to fit the following criteria:

  1. Safe and acceptable - it MUST be safe and something that society will accept. No one would accept performing a brain biopsy on all workers to ‘check’  if their mercury exposure had caused structural changes in the brain. It’s also not safe to do this en masse in a clinic or on-site. 
  2. Simple and cheap - You want to be able to do it without specialised equipment that requires years of training to be able to use. And each test cant cost thousands of dollars or it will be too prohibitive to do the test on workforces across the country.
  3. Accurate - Speaks for itself.
  4. Sensitive and specific with reasonable PPV - It has to be sensitive enough to pick up the changes in the body, and specific enough that you know that the changes it shows are due to the exposure. To achieve this, you need to know what the exposure does to the body and at what level of exposure it has the effect.

All of this is important because there can be serious consequences if the test that is chosen is wrong. If the test is not sensitive enough to pick up changes in the human body from an exposure you could miss a problem and make workers sick. If the test isnt specific enough then you could incorrectly think that a worker is sick due to an exposure at work, when they either aren’t actually ill or the test results are due to another cause.

This is a problem when a ‘scatter gun’ approach is taken to health surveillance. Someone has advised an organisation with workers who are exposed to isocyanates that every worker should get a chest Xray and a blood test. Now, isocyanates can cause respiratory disease, namely asthma, but a Chest Xray will not show this. And a blood tests are also of no value in diagnosing asthma. 

For the organisation, this is a waste of money. For the worker it is exposure to harm (radiation and being stabbed for a blood test) that is unnecessary. Worse still, what about the poor worker who is found to have a minor change in there Full Blood Count and is then further subjected to a barrage of tests to make sure that the changes aren’t dangerous? What about the worry that they go through thinking that they are sick, and blaming their workplace or colleagues for it? As doctors, we are supposed to follow a set of rules, the first being "Primum non nocere” or "First do no harm”. By doing the wrong test, we are potentially harming people.

So, what seems like a simple process of doing some tests because you have to, becomes quite a specialised process. And that’s before you even get to the stage of interpreting the test results.

The people who are best trained and qualified to advise you on Health Surveillance are Occupational Physicians. Look them up and see what they have to offer.