Regional Laboratory
AllianceRegional Laboratory
Alliance|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Colorectal cancer is the only major cancer that affects men and women almost equally. It is rare in persons under age 40, but the incidence begins to rise substantially after age 50. About 6% of people develop colorectal cancer by 80 years of age and 50% die as a result of the cancer. Three recent randomized, controlled trials have convincingly shown that the mortality rate can be reduced 15 to 35% by screening with fecal occult blood tests (FOBT). As a result of these studies, major professional organizations such as the American Cancer Society, the United States Preventative Service Task Force, the American College of Physicians, and the College of American Pathologists now recommend annual testing of all adults at 50 years of age or older. FOBT was also added to the list of approved Medicare Preventive Service Benefits on January 1, 1998.
Current guidelines recommend screening with a guaiac-based test such as Hemoccult II, which has been classified as waived test by CLIA ‘88. Patients should collect a total of six samples in order to compensate for sampling error since blood is not evenly distributed in stool. Two slides should be prepared from each of three consecutive bowel movements. The collection should be made 24 to 48 hours after eating a meat free diet and avoidance of vitamin C, aspirin, and nonsteroidal anti-inflammatory drugs. Slides need to be developed within 7 days of collection. Longer periods of storage cause weakly positive stools to become falsely negative. The dried stool specimens should not be rehydrated with a drop of water at the time of development because this practice increases the false positive rate up to 16%. A false positive rate of this magnitude leads to too many nonproductive colonoscopic examinations and makes screening impractical.
FOBT is considered positive if even one of the six slide windows turns blue. A middle-aged adult with a positive result on an initial FOBT (performed without slide rehydration) has a 7 to 14% probability of early colorectal cancer (Dukes stage A or B). The probability of early cancer or a large (>1 cm) adenoma is approximately 30%. Cancer detection rates are lower following rescreening. Nonetheless, cancer detection rates are high enough to warrant a complete evaluation of the colon and rectum whenever a person has a positive test either initially or at rescreening. If the results of colonoscopy are negative, FOBT does not need to be repeated for 5 years. If colonoscopy reveals cancer or a high risk adenoma, periodic colonoscopic surveillance is indicated.
A negative result on FOBT does not rule out colorectal cancer, because the sensitivity of the test is only 30 to 50%. FOBT should be repeated either annually or biennially. If symptoms develop that suggest colorectal cancer a more definitive test should be performed to rule out a neoplasm.
In 1994 the National Institutes of Health Consensus Development Conference concluded that Helicobacter pylori (H. pylori) infection represents the major cause of peptic ulcer disease, present in 90% of patients with duodenal ulcer and 80% of gastric ulcers.
Worldwide, the prevalence of H. pylori infection is estimated at 50%. The primary mode of transmission appears to be fecal-oral. In the United States the overall prevalence is 30-40%, with lower prevalence in younger age groups.
Immediately following infection, H. pylori causes acute gastritis. H. pylori is spontaneously cleared by some individuals, but causes persistent infection in most, which leads to chronic active gastritis. Subsequent complications include gastric and duodenal ulcers, and rarely gastric lymphoma, and gastric adenocarcinoma. An estimated 16% of infected individuals in the U.S. develop duodenal ulcers in addition to chronic active gastritis. Infection in early childhood increases risk for later development of gastric adenocarcinoma. Fewer than 5% of infected individuals will develop gastric lymphoma which may give rise to diffuse large cell lymphomas that are refractory to therapy.
H. pylori infection may be diagnosed by invasive (endoscopy) or noninvasive means. Complications including GI bleeding, weight loss, older age, or persistence of symptoms after antimicrobial therapy are indications for endoscopy. From endoscopy, the organism may be identified by culture, biopsy, or rapid urease testing (e.g. CLOtest).
Noninvasive testing includes serology, fecal antigen testing and urea breath testing.
· Enzyme immunoassay (EIA) for IgG antibody to H. pylori is the serologic method of choice for screening in uncomplicated dyspepsia. Serum IgG EIA’s have 90-95% sensitivity and 80-90% specificity. It should be noted that serum IgG assays have markedly reduced sensitivities in HIV-infected patients.
· Several rapid immunoassays have been developed that produce a qualitative result in 4-10 minutes. Compared with serum EIA’s, these whole blood rapid immunoassays have reduced sensitivities (80-90%), but comparable specificities.
· The noninvasive urea breath test (UBT) has excellent sensitivity and specificity for the diagnosis and assessment of patients post therapy (both exceeding 95%) when compared to invasive methods, however due to high cost, this testing is not recommended for routine screening in uncomplicated, untreated patients. UBT is useful in follow-up of patients who continue to be symptomatic despite antimicrobial therapy, and may confirm eradication of H. pylori within six weeks after therapy compared with a 6 to 12 month followup period with serology for IgG antibody.
· The newest FDA-approved noninvasive test is an EIA for detection of H. pylori antigen in stool specimens. Compared to other direct detection tests, the stool antigen test has sensitivity of 93-98% with specificities of 88-96%. Because the test measures H. pylori antigen it may also be of use to confirm eradication within a short period of time following therapy.
The antigen test is now available through Saint Luke’s Regional Laboratories. Fresh stool specimens should be submitted in an airtight container and refrigerated prior to transport. Stool in transport media, swabs, or preservatives are inappropriate for testing. Use of antimicrobials, proton pump inhibitors, and bismuth preparations prior to testing may cause false negative results. Testing will be performed twice weekly in conjunction with H. pylori IgG antibody.