The Institute for Quality and Efficiency in Health Care (IQWiG) has investigated the reliability of diagnosing bronchial asthma in children aged between 2 and 5 years, and the benefit that the test results can have for these patients. IQWiG published its final report in August 2009. According to the report, the available studies do not reveal any diagnostic procedure to be particularly suitable. It also remains unclear whether the treatment given based on the test results can benefit the patients.
The Federal Joint Committee (G-BA) commissioned the Institute to carry out the research. Using IQWiG expertise, the committee seeks an answer to the question whether the existing DMP should be extended to children of preschool age. Until now, it has only been possible to enrol children from the age of 5 upwards on a DMP.
Diagnosis must be certain
Bronchial asthma frequently starts in early childhood, but it is very difficult to diagnose in this age group. Moreover, young children are often free of symptoms by the time they reach school age. On the one hand, the screening should ensure no asthma cases are overlooked, so that appropriate treatment can be given in good time. On the other hand, children that do not actually suffer from chronic asthma should not receive unnecessary treatment and thus be exposed to potential harm. The certainty of the diagnosis is therefore of particular importance.
In the first report already completed, IQWiG investigated whether a reference standard could be derived from clinical practice guidelines, against which the diagnostic reliability of individual methods could be measured. The current optimum and most reliable method for diagnosing or excluding a disease is taken as a reference standard. As this type of test could not be identified, the Institute then investigated the accuracy of diagnostic procedures without using a reference standard.
No recommendation for diagnostic procedures can be derived from studies
In this second part of the commission, IQWiG investigated how suitable the procedures are in differentiating between those children who have symptoms but do not require long-term treatment and those children who develop chronic asthma. This ability to discriminate and predict is particularly important for those children who might have to be enrolled on a DMP.
After analysing a total of 7 studies available at that time, IQWiG came to the conclusion that the literature could not provide any recommendations for an individual method, or a combination of specific methods, that could be used as a criterion for enrolment on a DMP. The superiority of one test over any other could not be established.
This is firstly because there are only a few clinical comparisons dealing with the commission's research question. Secondly, the data contained in them have no validity, because the study and report quality displayed flaws. For example, there is a lack of data on the severity of disease in the patients examined, yet the degree of severity can have an influence on how reliably the test confirms the disease. The analysed studies indicate that a diagnostic algorithm could be used, i.e. a certain sequence in which individual measures can be combined together.
"Linked evidence" method could not be applied
In order to assess the diagnostic procedures, IQWiG also evaluated their efficacy. The tests can only be described as efficacious if they result in a therapeutic benefit, i.e. the patients can benefit from treatment. However, as the search revealed, there are currently no diagnostic studies that could provide a direct answer to the question of test efficacy (Phase 4 diagnostic studies), because this would require a study design that investigates a treatment strategy consisting of a test and an intervention.
If information on diagnostic procedures and therapeutic measures is only available in separate studies (Phase 2 and 3 diagnostic studies, and therapy studies), it is possible to try to synthesize and link them to a certain extent. In this way, at least indirect findings on the clinical efficacy of diagnostic procedures can be obtained. However, this method of "linked evidence" involves certain methodological requirements. As IQWiG and its external experts established, the studies available to date on diagnosing asthma in children under 5 years of age do not contain these requirements. Thus, a reference standard was particularly lacking.
No robust conclusions concerning efficacy possible
Even a modified procedure which, based on the linked evidence criteria, attempts to link the studies without a reference test is not possible. This is in part because the asthma-specific selection criteria are not precisely described in the therapy studies. Furthermore, none of the therapy studies used a selection method whose diagnostic accuracy had already been proven by studies.