What is diagnosis and why do we use it?

Diagnosis and the scientific ideology of reductionism go hand-in-hand. Reductionism is the belief that everything can be explained by the sum of its parts, i.e. that it can be reduced to one type of knowledge. So for psychiatry this means “that aspects of meaningful human behaviour can be fully explained in terms of ‘non-meaningful’ entities such as genes, neurotransmitters and ultimately atoms and molecules” (Bracken & Thomas, 2009, p 14). Diagnosis is a reductionist practice, where a label or diagnosis is said to represent an illness with a biological aetiology.  

Johnstone (2008), in explaining the purpose of diagnosis, writes first about how it functions in general medicine. She states that it is used as an essential first step to determine the appropriate treatment and then goes on to detail a list of other preferred, but not essential, criterion that are often also fulfilled. These include; that it gives information to patients and families who want to know what condition they are suffering from, gives details of prognosis, allows professionals to communicate in shorthand, provides a basis for research, informs aetiology, and signposts patients and their families towards appropriate services and resources. 

How suited then, is diagnosis to the field of psychiatry where medical causes, such as ‘biochemical abnormalities’ and ‘genetic vulnerabilities’, are still only working theories, rather than established facts (Bentall, 2009; Johnstone, 2008)? Psychiatry, as with natural sciences such as chemistry, biology and physics, relies upon the ability to use valid and reliable categories or units as a way of testing hypotheses and developing theories. In medicine the ability to define and classify different illnesses allows for hypotheses about prognosis, aetiology, and treatments that can then be tested (Johnstone, 2008). In summation, the medical model and psychiatry needs classification of its units of study, to act as objective truths, so that it can then engage in scientific thinking, but does our understanding of distress need, or benefit from, it’s classification?