When it comes to the CTA Written Exam you will be asked to have a diagnosis for your chosen client (Section C). You will in fact be asked to detail this diagnosis by using two accepted systems of diagnosis. Usually this will be a TA diagnosis and a classification using DSM1V.
The course will give you a basic understanding of DSM1V and therefore allow you to classify your client using the system. The course will also make reference to ICD10 and how this applies to the UK.