Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1308 page)

   
D
-xylose results can be normal in malabsorption syndromes caused by pancreatic insufficiency.

   False-positives can occur with decreased renal function, dehydration/ hypovolemia, surgical blind loops, decreased gastric emptying, vomiting.

   Patients should not eat foods containing high levels of pentose, including fruits, jams, jellies, and pastries for 24 hours prior to test.

   Low values can also be caused by inflammation of the lining of the intestine, short bowel syndrome, and infection with parasites, like giardiasis or hookworm.

   Blood
D
-xylose levels are generally considered more reliable than urine levels in children younger than 12 years old.

ZINC (Zn)

   Definition

   Zinc, an essential trace element, is the intrinsic metal component or activating cofactor for more than 70 important enzyme systems, including carbonic anhydrase, the ALPs, dehydrogenases, and carboxypeptidases. It is involved in the regulation of nucleoproteins and the activity of various inflammatory cells and plays a role in growth, tissue repair and wound healing, carbohydrate tolerance, and synthesis of testicular hormones. Zinc intake is closely related to protein intake; as a result, it is an important component of nutritionally related morbidity worldwide. Symptoms attributable to severe zinc depletion include growth failure, primary hypogonadism, skin disease, impaired taste and smell, and impaired immunity and resistance to infection. Subclinical zinc deficiency may significantly increase the incidence of and morbidity and mortality from diarrhea and upper respiratory tract infections. Along with iron, iodine, and vitamin A, zinc deficiency is one of the most important micronutrient deficiencies globally. Several studies have now demonstrated that supplementation of high-risk populations can have substantial health benefits.

   
Normal range:
(see Table 16.89).

TABLE 16–89. Normal Range for Zinc by Age

   Use

   Detecting zinc deficiency

   Assist in confirming acrodermatitis enteropathica