[Strategies for investigating non-assimilation. A critical status]

This review reevaluates the rational basis for choice of diagnostic strategies in patients with suspected malassimilation. Prospective evaluation of diagnostic tests must fulfil several requirements for a correct assessment of their clinical value. Very few studies meet such requirements, resulting in unnecessary investigations as well as overlooked cases with a negative impact on patients and society. This problem includes evaluation of assimilation of macronutrients (carbohydrate, fat, protein) as well as micronutrients (e.g. vitamin B12), and it is further complicated by the occurrence of conditions with occult (compensated) malassimilation. Malassimilation of carbohydrates may be physiological (starch, fructose, sugar alcohols etc., in certain ethnic groups lactose) as well as pathological. In both instances chronic gastro-intestinal distress may arise in sensitive individuals. The diagnosis is based on tolerance tests, combined with blood tests or breath tests (hydrogen excretion). The latter is considered the most reliable, but the available evidence for choice of tests is not solid. Similar reservations apply to conditions of bacterial overgrowth of the small intestine, which may lead to diffuse malassimilation. The frequency and clinical importance of this condition is in all probability underestimated. Screening for coeliac disease may be achieved by several serological tests (reticulin-, gliadin-, endomysial antibodies), of which IgA-endomysial antibodies seem superior. Comparative studies are often flawed in design, however, and permeability tests may also eventually find their place in the test battery. There is thus a strong need for more evidence-based diagnostic strategies in patients with suspected malassimilation.