Understand the relative contributions of clinical laboratory tests and other diagnostic studies in the evaluation of the patient for a disorder of the gastrointestinal tract.
Learn the appropriate selection of diagnostic tests required to establish a diagnosis of ulcer disease from Helicobacter pylori infection.
Select the most appropriate tests for evaluation of suspected celiac disease, and learn the situations where results may be misleading.
Understand the causes of both upper and lower gastrointestinal bleeding.
Describe the recommended approaches to screening for colon cancer, and the benefits and limitations of laboratory tests for this purpose.
Most diseases of the gastrointestinal tract can be directly visualized by endoscopy or from a histopathologic review of a biopsy obtained during the endoscopic procedure. In addition, many gastrointestinal tract disorders can be identified with various imaging studies. This accessibility of lesions for direct examination and biopsy, and the availability of imaging studies, has limited the need for clinical laboratory tests in identifying most gastrointestinal disorders. However, imaging studies are often expensive, and endoscopic procedures are both expensive and invasive. Laboratory tests aid in the diagnosis and management of patients with a number of gastrointestinal disorders. Infectious diseases involving the gastrointestinal tract are numerous, and are discussed in Chapter 5. The clinical laboratory plays an important role in identifying pathogenic microorganisms of the gastrointestinal tract.
The clinical laboratory also plays a role in the evaluation of dyspepsia (abdominal discomfort caused by acid), and/or ulcer disease, particularly that induced by Helicobacter pylori infection; in the recognition and monitoring of celiac disease; identification of gastrointestinal bleeding and the causes for it; and in the detection and genetic profiling of colorectal cancer. Laboratory tests for these disorders are presented in this chapter.
DYSPEPSIA, ULCER DISEASE, AND H. PYLORI
According to the American Gastroenterological Association (AGA), dyspepsia is defined as chronic or recurrent pain or discomfort centered in the upper abdomen. There are several common causes of pain the upper abdomen. Reflux of acid into the esophagus, referred to as gastroesophageal reflux disease [GERD] can cause abdominal discomfort. There is great variability in incidence between countries among those with upper abdominal symptoms who are found to have peptic ulcers. Other causes for abdominal pain include gastritis related to use of nonsteroidal anti-inflammatory agents, and functional dyspepsia, in which no obvious pathology is present in the stomach.
The major cause of peptic ulcer disease is infection with H. pylori. The infection is most likely to occur in childhood, especially if the children are living in low socioeconomic conditions. In developed countries, H. pylori infection prevalence increases with age. Not all patients with H. pylori infection develop ulcer disease, as many suffer from dyspepsia without ulcers. The infection initially produces an acute gastritis that lasts 1 to 4 weeks. Once infected, however, chronic active gastritis ...