The question often arises as to which Lyme test guarantees diagnostic value.
The initial answer is that no test can establish a diagnosis, because that is done by a doctor, even according to the latest recommendations, primarily on the basis of the clinical picture.
However, there are tests that can reliably support the diagnosis because they have undergone the appropriate research and approvals.
Tests that detect infection
It is important to know that there are basically two types of tests for Lyme disease. One type can detect infection (and, in the best case, its level), i.e. whether there are pathogens in the sample. This provides a yes or no answer. However, the fact that the infection is present does not necessarily mean that it causes symptoms. An example of such a test is when we have a sore throat and our GP takes a swab. The sample is then placed on various culture media in the laboratory and examined to see if anything has “grown”. Basically, the laboratory gives a yes or no answer for the pathogen in question. It is then up to the doctor to decide which bacteria are contributing to the symptoms. In the case of Lyme disease, most tests fall into this category, providing information such as the level of immune response, but cannot be used to make a diagnosis.
Tests that can determine the diagnosis
The other type of test is when the method is able to provide a reliable result about the patient’s condition in a clinical situation – as if the test were the only thing used to make the diagnosis. There are methods that are theoretically incapable of doing this in a real-life situation. For example, it is known that neither serological IgM nor IgG results correlate completely with whether a patient is healthy or sick, especially after successful treatment or in seronegative cases. Genetic methods (PCR) currently fall into the former category because they only show that the pathogen is present, but it is not necessarily proven that it causes disease.
In order to obtain reliable diagnostic results, much more than theoretical compliance is required. The usual “performance evaluation test” in such cases is generally a clinical study. For this, a clinical research plan is usually required to be published in advance and cannot be changed later. The research must have a sufficient number of subjects and provide evaluable statistics, with a minimum of 60-70 subjects per group and a 95% confidence level. The research must be coordinated and conducted by an independent organisation. The research must be approved in advance and the results must be reported to and accepted by the authority. If the research is successful and the statistics show sensitivity and specificity in line with the original objectives, official approval can follow.
The end of the regulatory approval process is approval by the FDA in the US and IVD CE marking in Europe. European approval requires locally conducted research, which is particularly important given the varying nature of Lyme disease across continents and even countries. Research data is usually published in internationally recognised journals and presented at conferences, but this is not mandatory – often, the results only appear in sponsored articles.
Is the test reliable?
Compliance with the above diagnostic criteria can confirm that the test is indeed “diagnostic”. If there is not a sufficient number of independent studies behind it, or if it is not approved, the test cannot provide “diagnostic” value.
There are tests that serve both purposes and also provide information on the level of infection and positive-negative categories.
Before attempting to interpret the test results, please check what European research and authorisation underpin its use. If this is not indicated on the result, ask your service provider for the document certifying IVD CE registration.
