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The irritable bowel syndrome is the commonest functional gastrointestinal disorder seen in both primary and secondary care, [1 2] and studies have shown that symptom complexes compatible with the clinical diagnosis of irritable bowen syndrome may be present in up to 30% of the general population. [3 4] Most people with gastrointestinal symptoms never consult doctors about them ; previous studies on dyspepsia, for example, have shown that concern about the possible serious significance of symptoms is a major determinant of consultation behaviour.  This is likely to be true for irritable bowel syndrome also.
Traditionally, irritable bowel syndrome has been a diagnosis of exclusion, made only after organic disease has been ruled out by investigation. Unnecessary investigations not only involve costs to the health services but also may increase diagnostic uncertainty and heighten patients' anxiety. In an attempt at greater precision, Manning and his coworkers reported the prevalence of 15 symptoms in irritable bowel syndrome and compared these with symptoms in patients with organic disease.  They concluded that six cardinal symptoms discriminated the painful variant of irritable bowel syndrome from organic bowel disease. The more of these six symptoms that were present, the more likely it was that the patients had irritable bowel syndrome. Subsequently Thompson examined the discriminatory value of four symptoms--abdominal pain relieved by defecation, abdominal distension, and both looser and more frequent bowel movements with the onset of pain--and concluded that if two or more of these symptoms are present irritable bowen syndrome could be discriminated from peptic ulcer or organic bowel disease.  Talley and colleagues have evaluated the reliability and discriminatory value of the Manning criteria in irritable bowel syndrome by using an objective self report questionnaire.  Their findings suggest that these criteria can discriminate subjects with all forms of the syndrome from healthy controls and also from patients with organic gastrointestinal disease, although a recent study has cast some doubt on the diagnostic utility of the Manning criteria in men. 
There is also interesting evidence of disease associations with irritable bowel syndrome. A substantial number of patients also have abnormalities of bladder detrusor muscle function,  and associations with a variety of urinary and gynaecological symptoms and with headache have been noted. [12 13] Most recently, patients with irritable bowel syndrome and without respiratory symptoms have been shown to have abnormally responsive airways after methacholine challenge, compared with normal controls and patients with organic bowel disease.  The possibility that a generalised smooth muscle abnormality underlies all these conditions is a subject of considerable research and potential therapeutic interest.
Irritable bowel symptoms are common in the general population and in patients with organic disease,  and the predictive value of any criteria will vary according to the prevalence of the disease in the population being assessed. Most people with symptoms will not present for medical care and it is …