Tag Archives: selective testing criteria

“Quality, not quantity…”

Whenever I am thinking about a new test Y, which is superior to the old (incumbent) one X, but costs more money, then the first thing I do is calculate the “disease budget”. i.e. I will find out the cost of our current test to diagnose that condition (and any other related tests) and multiply it by the number of tests we do to get the total amount of money spent on that specific disease/infection.

I can then work out how many tests we can perform with new test Y, and consider implementing selective testing criteria in order to focus testing on those patients that most require it.

Short of getting more money from lab funders for the “disease budget”, which is occasionally necessary, but very difficult to achieve , this is one of the few ways that we can introduce better (but more expensive) tests into our armoury. (Another possible route is utilising other disease budgets which have become redundant, i.e. rotavirus testing dramatically decreased due to childhood vaccination, so the money used for rotavirus testing could be used to fund the diagnosis of another faecal pathogen.)

We know that a combination of poor sensitivity and long turnaround times affects a lot of the traditional tests that we currently use in the microbiology department.

But it is not good enough to simply say, “These new tests are just too expensive for our budget”.

We owe it to our patients to play the system and work out ways of getting better, albeit more expensive tests on to the menu.

I prefer to use good tests well, on the right patients, and where real-time results can make real-time differences to patient management.

When strict clinical “qualifying” criteria are set up for certain tests, there will always be a few grumbles from requestors “Why can’t my patient get test Y”. This is when the 3Es, empathy, education, and explanation of the criteria are required. Even then, you can be sure that you will never keep everybody happy…

It is very rarely that we, in the microbiology department, audit how often the hundreds of results that we report out actually make a real time difference to the patients.

I suspect we shy away from this type of audit because the results would probably scare the living daylights out of us, and our funders…

Quality, not quantity.



“Cutting off the fat whilst keeping the flesh”


Reducing inappropriate or unnecessary testing is generally a good idea. Not only does it free up finances which can then be used on other more useful tests, it also improves the positive predictive value of the test in question by increasing the prevalence in the tested population.

But how exactly do you reduce inappropriate testing? Well you can look at guidelines from other centres or research papers published in journals. But in my opinion the best evidence to support reducing inappropriate or unnecessary testing is to collect your own localised data. This is particularly the case if you want to reduce unnecessary testing by introducing specific testing criteria based on certain patient or laboratory parameters.

For example if you want to restrict Hepatitis A testing to those patients with a significant ALT increase, then you need to look at the range of ALT values for all your patients with a genuine positive Hepatitis A result.

If you want to restrict Trichomonas testing to all those patients under a certain age, then you need to examine the age related prevalence rates for Trichomonas in your particular population.

The risk with cutting off the fat however is that you always risk cutting off a little bit of the flesh, i.e. you may miss the occasional positive where the patient has fallen outside the pre-determined testing criteria for that particular infection.

The key is in deciding whether the criteria or the cut-off level for testing that you have set are acceptable, and to do this you need to take into account as a minimum the severity of disease, the consequences of a missed diagnosis, the opportunity/potential to make the diagnosis at a later date. This is why you would never dream of restricting testing for syphilis in community age groups over a certain age, just because the prevalence in this cohort is so low. Because if you miss the diagnosis of syphilis the consequences could be a lot worse than if you missed a trichomonas infection…..

But possibly the most important factor to take into account when trying to adopt selective testing criteria is to consult with and gain approval from requestors, and in particular specialists in that particular area of testing. Thus it is a good idea to have good working relationships with the Infectious Diseases department and for that matter all your other users as well.

The requestors generally understand the situation. they will often be budget holders in their particular area/institution and understand exactly what you are trying to achieve. If you are reasonable, rational and communicative, only rarely will they stand in the way of what you are trying to achieve.

And the flesh and fat analogy works well in my opinion. If you try to cut off too much fat, then you will start removing the flesh as well, and you will only end up hurting the patient….