DIFFERENTIATION OF OSMOTIC AND SECRETORY DIARRHEA BY STOOL CARBOHYDRATE AND OSMOLAR GAP MEASUREMENTS

Clinical features and laboratory tests that determine carbohydrate in faeces were evaluated to determine which was best able to distinguish between osmotic and secretory diarrhoea in infants and children. For t his purpose 80 boys aged 3 to 24 months, with acute watery diarrhoea, were studied prospectively. The faecal osmolar gap (FOG) was calculate d as: serum osmolarity - [2 x (faecal sodium + potassium concentration )], Fifty eight patients were classified as having predominantly osmot ic diarrhoea (FOG >100 mosmol/l), and 22 as having predominantly secre tory diarrhoea (FOG less than or equal to 100 mosmol/l). The two group s were comparable in their clinical features on admission, in the resu lts of blood and urine tests, and in the evolution of their diarrhoeal illness. Evidence of steatorrhoea (by positive Sudan III test) and of acid faecal pH on admission were significantly more frequent in patie nts with osmotic diarrhoea. Mean (SD) faecal osmolarity was not signif icantly different between the two groups (319 (80) mosmol/l in secreto ry diarrhoea v 361 (123) mosmol/l in osmotic diarrhoea). Tests for red ucing substances in faeces such as Benedict's test - with and without hydrolysis - and glucose strip, all showed a positive and significant association with osmotic diarrhoea (p <0.05, <0.025, <0.05, respective ly). The presence of excess reducing substances (Benedict's test with hydrolysis >++) on admission was the most sensitive and specific test with the best predictive value for differentiating between the two typ es of watery diarrhoea.