How is CFS diagnosed?

There is no laboratory test which can be used to diagnose CFS. Instead, diagnosis relies on careful evaluation of the patient's history and exclusion of other conditions by the doctor. The patient must then fulfil the case definition for CFS. Laboratory tests can be used where indicated to exclude other conditions. Some laboratory tests (eg. immunological tests) can be used as evidence to support the diagnosis, but alone have no diagnostic value in the syndrome. Sophisticated laboratory tests are research tools, and are not used in routine diagnosis of the illness. The patient's history (eg. sudden onset of a 'viral' illness and typical symptoms) often points to the likelihood of CFS.

There are three sets of diagnostic criteria for CFS in use, which are generally similar. The criteria devised and used by the researchers at The Prince Henry Hospital are as follows:

The patient must have:

1) Chronic persisting or relapsing fatigue of a generalised nature, exacerbated by minor exercise, causing significant disruption of usual daily activities, and present for greater than six months.

2) Neuropsychiatric dysfunction including impairment of concentration evidenced by difficulty in completing mental tasks which were easily accomplished before the onset of the syndrome; and new onset of short term memory impairment.

3) No alternative diagnosis reached by history, physical examination or investigations over a six month period.

Researchers have decided that people with the symptoms of CFS must be unwell for a minimum of six months before being given the diagnosis of CFS. While somewhat arbitrary, this requirement recognises the fact that delayed recovery after viral or other infections is very common in the community, and serves to distinguish those with short-term illness from those with longer-term (or chronic) illness, ie. CFS.