Testing for intestinal permeability is a sensitive and accurate way to screen for celiac disease, with fewer false positive and false negative results than other commonly used screens. Intestinal permeability reflects the ability of the intestinal lining to absorb nutrients while keeping undesirable chemical substances out of the body. In patients with celiac disease who are consuming gluten, even small amounts of damage to the intestine will allow certain large chemical molecules to leak into the bloodstream, from which they may be excreted by the kidneys into the urine. The available permeability test requires that the individual drink a solution which contains two sugars, neither of which is metabolized or changed in the body. One sugar is usually mannitol, which is readily absorbed from the intestine and excreted in the urine. The other sugar is lactulose, which is hardly absorbed at all under normal conditions. Any lactulose that is absorbed is excreted unchanged in the urine within 5 to 6 hours. Both sugars are safe to be taken, even by small children. When a person with celiac disease drinks the lactulose/mannitol mixture, an excessive amount of lactulose will appear in the urine, unless the person is on a strict gluten-free diet. If the person has enough celiac disease to create malabsorption, then the mannitol level in urine will be low. The ratio of lactulose to mannitol in urine is the most sensitive index of active celiac disease. An elevated lactulose to mannitol ratio in urine may be due to conditions other than celiac disease, such as intestinal infection, severe food allergy or Crohns disease, but a normal ratio indicates either that the person does not have celiac disease or is in complete remission due to strict adherence to a gluten-free diet. Information about this test can be obtained from the one laboratory that presently offers it, Great Smokies Diagnostic Laboratory in Asheville, NC. Their number is 1-800-522-4762.