To test or not to test …

You would think that being able to test for a disease or a condition is always a good thing, and we should do whatever tests we can to be certain we are making the right decisions or giving the best care. You would be right, sort of. It is pretty much always better to be able to test than not to have that option. For example, there is no test for multiple sclerosis (MS) and it would be rather useful if there was. Or maybe sepsis is a better example. Sure there are things we can test to help us diagnose MS or sepsis, but there is no definitive test that indicates either of these conditions. In the case of sepsis, not getting to the diagnosis quickly can have very bad consequences.

What about where we do have a test? Is it always beneficial to do it? Look at a tension pneumothorax as an example. It is certainly possible and definitive to do a chest X-ray to confirm that the trauma victim has a tension pneumothorax, but most trauma professionals would agree that if you haven’t treated it before you got as far as doing a chest X-ray, your knowledge and skills need serious attention.

Another example of testing perhaps being less useful than we might think was when my wife was pregnant with our third child. She declined an amniocentesis test because when she asked why it should be done, the health practiitoner told her that is was so she could choose to terminate the pregancy if there were defects noted. Since she was not prepared to consider that possibility unless her life was endangered, she declined the test, and copped quite a bit of pressure from well-meaning people for it. To add weight to her decision, the test was not without its own risk of causing miscarriage, so why do it when there’s no benefit?

The question I always ask is, “What will we gain by doing this test/procedure/intervention?” When I was learning to be a Nurse Practitioner, and working in a busy Emergency Department on night shift, I adopted the approach that tests are only useful if the result will change my management of the patient. This was particularly relevant on night shift, because we had to call in the hospital scientist to do pathology tests after hours, or the on-call radiographer to do X-rays. Where the results were unlikely to to make any difference to the management of the patient before morning, the decision was to leave the tests until then. Of course you had to have confidence in your clinical decision making to know when it was OK to wait, and when tests really did need to be done immediately. One of the useful techniques I used was to make a note of these decisions and review them the next day to see if I missed anything. Of course I made mistakes, but over time, I became less reliant on testing for everything just because I could.

Let’s move on the topic of the times – COVID testing using the PCR (polymerase chain reaction) method in a pathology laboratory. It is a triumph of science that we have a safe and reliable test for COVID-19 infection, even in people who are completely well. In the 1918 influenza pandemic, there was no test other than people getting sick and dying, and no-one knew who the asymptomatic carriers of infection were. So it would appear that we have a fantastic tool to help beat the COVID-19 pandemic that our forbears did not have. Therefore it would appear obvious that getting everyone tested would be a good thing. But is it?

I think the answer is multi-threaded. On one thread, it is absolutely beneficial to know the COVID-19 infection status for as many people as possible during an outbreak, so blanket testing is necessary. On another thread, testing takes time and resources, so we need to weigh up whether the benefits are enough to justify the costs, and they usually are. A third thread is the dissemination of results, where a timely result will make a significant difference to such activity as contact tracing and quarantining or isolation of positive cases. This is where we run into problems. Let’s look at a case study:

Day 1: Wastewater testing in our community finds virus fragments specific to the virus which causes COVID-19. This test tells us that someone in the wastewater catchment area has COVID-19, or that someone with COVID-19 was in the area recently. It does not tell us who that person was. So we begin testing everyone in the community who has any symptoms that might be due to COVID-19.

Day 2-5: Testing continues and results of these tests are received within 2-3 days. Some postive cases are found. Contact tracing commences and testing is ramped up to include all residents of the community. Results begin to slow, and some even go missing.

Day 6-14: Testing of the entire community is undertaken, with some people such as frontline health staff and police being tested repeatedly. Results begin to take over a week to arrive, and some never arrive. This is where the incredible value of testing as a pandemic control tool begins to lose ground. Unless the results are available quickly enough to make a difference, then people begin to ask what’s the point. And they are right. Here we have one of the best tools we have being blunted by lack of timely output.

Travellers wishing to leave the area initially needed to have a PCR test no more than 72 hours before entering some other jurisdictions, but it took over a week to get the result by which time it was invalid. It was and is currently not possible to get a result within 72 hours as the pathology laboratories are overwhelmed with the volume of testing. We absolutely do not want to abandon testing, so how can we fix the problem?

One solution is to formalise Rapid Antigen Testing (RAT) for travellers and asymptomatic people who are not close contacts. It takes 15 minutes rather than over a week to get the result, and is safe and reliable. Some jurisdictions will not accept a negative RAT for entry but still require the negative laboratory test within the 72 hours prior to entry. This in effect means that no-one can enter that jurisdiction as they have to obtain a test result that is unobtainable in that time frame. Part of the issue may be that the RAT is self-administered and human nature being what it is, some COVID positive people may game the system to get across borders. If border control could somehow include supervision of RATs for travellers, or clever technicians work out an electronic means of doing this, it would reduce the risk of misuse. Using the RAT for widespread community testing of well people would give much more timely results, with only the unwell or those with a positive RAT needing the laboratory test. This would help ease the enormous pressure on pathology laboratories, allowing them to focus on testing close contacts, people in quarantine and isolation, and people who have a positive RAT. That will resharpen our tools for bringing the pandemic under control.

Going back to my opening points about testing, COVID-19 testing is only useful if we know the results of the test in a timely manner. Where results are so delayed that they are meaningless, resources are being spent needlessly. Rapid Antigen Testing may give us a way forward to get back timely test results, which will make the whole COVID-19 testing regime less frustrating for clinicians, community members, and travellers. PCR testing via a pathology laboratory is still vital but I think it should be reserved for where it is most needed, and the RAT used as the first line of testing in the community for most people.

Disclaimer: This post is entirley my own thoughts and ideas and does not represent the position of my employer or the government of the jusrisdiction I live and work in. I am not an epidemiologist or a pathology scientist, so welcome any comment if I have misunderstood the issues.

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