ADHS-Diagnosemethoden: Verfahren, Tests und diagnostische Kriterien

ADHD - Diagnostic methods - Introduction

Author: Ulrich Brennecke
Review: Dipl.-Psych. Waldemar Zdero (08/2024)

An ADHD diagnosis is traditionally determined using questionnaires, interviews and tests. In principle, several different instruments should be used. This means that several questionnaires, several tests and a personal interview by the diagnostician are essential for a good diagnosis.
The agreement between questionnaires and tests is limited despite the validity and reliability of the respective tests being checked.
Symptoms of ADHD also occur in other disorders. A study of 10 disorders found that 60% of the symptoms occurred in at least half of all disorders and were assessed in the respective disorder-specific questionnaires and tests.¹

ADHD is typically diagnosed by the number of relevant symptoms. This increases the diagnostic accuracy of ADHD.² This model was exemplified by Barkley:

Non-affected people often have 1 to 2 of 18 symptoms on average (around 5%)³
On average, people with ADHD often have 12 of these 18 symptoms (around 66%)³
The online screening of the ADxS.org symptom test is based on this model. It queries 45 symptoms, but is not medically validated and is not used for medical diagnosis.

Neuropsychological tests⁴ or individual biomarkers are too imprecise to diagnose ADHD. We suspect that, similar to the rating scales for symptoms of ADHD, which are based not only on a single symptom but on the cluster of symptoms common in ADHD, a test cluster of a group of neuropsychological tests or measurement of a group of biomarkers typical of ADHD could result in adequate test accuracy. Since ADHD is a syndrome, i.e. a multitude of different causes that manifest themselves in common symptoms, biomarkers should only be able to either measure the mechanisms that mediate the common symptoms (although here too, with the dopamine and noradrenaline systems alone, there are several similar, because functionally redundant, systems) or recognize individual causes of the syndrome, but barely all of them. Against this background, it is surprising that the improvement of the detection rate through individual biomarkers continues to be pursued instead of researching the appropriate combination of different biomarkers that, in their entirety, enable ADHD diagnostics. There are individual approaches that pursue this idea.⁵⁶⁷

The agreement in the recognition of ADHD symptoms between different diagnosticians was found to be 0.68 in one study. The agreement in the recognition of changes in ADHD symptoms was 0.73.⁸

Sensitivity: People with ADHD are correctly recognized as people with ADHD

Example: Sensitivity of 85 %: Of the persons with ADHD, 85 % are correctly identified as people with ADHD and 15 % are incorrectly identified as people without ADHD (false negative). 15% of people with ADHD are not recognized.

Specificity: Non-ADHD persons are correctly recognized as non-ADHD persons

Example: Specificity of 91 %: Of the non-affected persons, 91 % are correctly identified as non-affected and 9 % are incorrectly identified as people with ADHD (false positive). Of the subjects assessed as having ADHD, 9% are not actually affected

As sensitivity and specificity are directly negatively correlated (a cut-off that causes a high sensitivity also triggers a low specificity), both values must be shown as a function of each other. This is not yet fully implemented in the following table.

Kappa: Comparison of observed agreement between raters with the expected agreement in the case of random agreement (1 would be perfect)

AUC: Area under the curve; selectivity 0.5 = 50 % = coincidence; 1 = 100 % = perfect

0.5 - 0.6 / 50 % - 60 %: very poor
0.6 - 0.7 / 60 % - 70 %: poor
0.7 - 0.8 / 70 % - 80 %: acceptable
0.8 - 0.9 / 80 % - 90 %: good
0.9 - 1.0 / 90 % - 100 %: excellent

The accuracy of clinical questionnaires should not be overestimated. Even very renowned standard tools should not be misunderstood as an objective benchmark.
A significance of 80 % and a specificity of 80 % are assumed to be appropriate.⁹ These values are barely achieved by a single test for ADHD. A combination of several tests is therefore required to diagnose ADHD.
However, sensitivity and specificity are not the only relevant criteria for a questionnaire.

There are studies that attempt to create a screening from 2 questions of the ASRS-18.¹⁰¹¹
In view of the fact that ADHD is a syndrome that is fed by a variety of different causes, we view these trends with great concern.

An exaggeration may make it clear: You could create a perfect questionnaire with just one question, with a sensitivity of 100% and a specificity of 100% if answered truthfully. The question is: “Do you have ADHD?”
This satire aims to illustrate that the fewer questions are asked, the more meta they are and therefore the more difficult it is for people with ADHD to answer them than questions that are aimed at life facts, of which many more are needed for a reliable assessment.
In a nutshell: We are very skeptical as to whether it is good for science that more and more studies on ADHD rely exclusively on self-report on the 6 questions of the ASRS, and we view this development with concern.

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