Seeking clues for a positive diagnosis of the irritable bowel syndrome.

Despite its high prevalence the irritable bowel syndrome (IBS) lacks acceptable pathophysiological markers and its diagnosis largely depends on the exclusion of underlying organic disease. Systemic acid-base balance, serum electrolytes and the composition of faecal water (electrolytes and organic anions), were studied in thirty-eight diarrhoeal patients out of a series of ninety-three consecutive IBS patients. Only patients with diarrhoea as the predominant symptom were included in the study to evaluate whether this subgroup could provide the clue for a positive diagnosis of the syndrome. Serum electrolytes and systemic acid-base balance were within the normal range. Faecal electrolytes were also normal (Na 26.6 +/- 19.3 SD; K 66.8 +/- 28.3; Cl 19.1 +/- 15.2 mEq 1(-1)), despite the finding of a moderately increased 24-h faecal output. The K:Na ratio was also within the normal range. These data are in agreement with the lack of systemic changes observed in IBS patients even with profuse or longstanding diarrhoea. Both faecal short chain fatty acids and lactic acid were increased in patients vs. controls, but a considerable overlap with normal values was observed (131.4 +/- 62.6 SD vs. 108.5 +/- 58.3 mEq 1(-1). Only lactic acid concentration was significantly higher than in controls (1.3 +/- 1.2 vs. 0.5 +/- 0.2). Despite these findings it is concluded that the subgroup of IBS patients with diarrhoea also appears to lack a pathophysiological marker and does not provide clues for a positive diagnosis of this syndrome.