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A false positive urobilinogen reaction may occur with the dipstick method when substances known to react with Ehrlich's reagent such as sulfonamides and p-aminosalicylic acid are present in the urine. Drugs that contain Azo dyes, such as Azo Gantrisin®, have a gold color that masks the reaction, causing a false positive reaction. Atypical color reactions may be obtained in the presence of high concentrations of p-aminobenzoic acid. The dipstick urobilinogen test cannot detect porphobilinogen in a urine specimen. Porphobilinogen is a molecule formed during the synthesis of the heme portion of hemoglobin.

The typical daily diet of most Americans contains approximately 10 to 15 mg of iron. Sources of dietary iron include heme iron from meats and nonheme iron from whole grains and vegetables. Many processed foods, such as breakfast cereal, are fortified with iron. However, the normal individual absorbs only 5% to 15% of dietary iron, or about 1 to 2 mg daily. Females may absorb slightly more iron than males as they require more iron to replace that lost through menstruation and to meet the increased need for iron in pregnancy.Absorption of iron occurs through the mucosal cells in the duodenum (proximal small intestine). Dietary iron that is not absorbed is excreted in the feces. Intestinal absorption provides the means for regulating the amount of iron in the body.The amount of Iron absorbed is normally low because iron is well conserved within the body. Heme iron from senescent erythrocytes is cycled back into the iron pool and reused for incorporation into developing erythrocytes. Furthermore, iron is normally lost from the body only in very small amounts, primarily through desquamation of mucosal cells in the gastrointestinal tract and losses through body secretions, including urine, sweat and feces. Therefore, under normal conditions, very little dietary iron needs to be absorbed to maintain iron homeostasis.(3)