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PTD - 230

Test Directory - Faecal Reducing Substances

Clinical Indications

Patients with carbohydrate malabsorption either cannot absorb a sugar or do not have the enzyme to break down a sugar. In lactase (converts lactose to glucose and galactose) deficiency lactose is not digested and absorbed but ferments to lactic acid with production of gas. This causes abdominal pain and diarrhoea which may be persistent and severe especially in young children.

Stools from patients with carbohydrate malabsorption are characterised by being liquid, frothy and acidic. Faecal pH has not been found to be reliable as a screening test for sugar malabsorption.

Faecal reducing substances using the (now obsolete) Clinitest tablet method were in use, but results were uninterpretable; positive results are seen in normals and negative results in patients with disaccharidase deficiency. Often dietary restriction of lactose is necessary as an empirical test or alternatively, the hydrogen breath test may be required - please contact Gastroenterology department for further information.

Paediatrics: If the baby is otherwise well and the problem is only loose stools then perseverence with feeding may be an option (to see if the problem resolves within a few days) or try an alternative milk based formula for a trial period. If there is evidence to suggest cow's mild protein intolerance this requires further testing to confirm and referral to a paediatric dietician / paediatrician if there is other significant evidence of allergy. If the problem is persistent or is more than just loose stools then the infant requires referral to a paediatrician/paediatric gastroenterologist.

Request Form

Combined Pathology Blood form (Yellow/Black)


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Lab. Handling

Processing: FRS and store at 4C in the separating fridge (CB39).

Version 1.0 / May 2014                                                                                                           Approved by: Consultant Biochemist