Fecal Occult Blood Tests Reduce Colorectal Cancer Mortality

Clinical Question

Should physicians use fecal occult blood testing to screen for colorectal cancer?

Evidence-Based Answer

Fecal occult blood testing reduces colorectal cancer mortality by 16 percent. Annual testing and rehydration of samples increases testing sensitivity but also increases the number of false-positive results.

Practice Pointers

Colorectal cancer is the third most common cancer in the United States, affecting 46 out of 10,000 women and 63 out of 10,000 men. U.S. Preventive Services Task Force and American Cancer Society guidelines recommend multiple options for screening average-risk patients. These options include annual fecal occult blood testing, flexible sigmoidoscopy, home fecal occult blood testing plus flexible sigmoidoscopy, colonoscopy, and double-contrast barium enema.1,2 Average-risk patients are those with no history of rectal bleeding, adenomatous polyps of the colon, or inflammatory bowel disease. There are specific screening guidelines for patients who have a family history of colorectal cancer or genetic cancer syndromes. Most higher-risk patients require a colonoscopy for initial screening.2

This Cochrane review included four randomized controlled trials (329,642 total patients) of fecal occult blood testing to screen for colorectal cancer. Outcomes included test sensitivity and reduction in all-cause and colorectal cancer mortality.

The review showed that fecal occult blood testing reduces colorectal cancer mortality by 16 percent (relative risk = 0.84; 95% confidence interval [CI], 0.78 to 0.90). Rates of patient compliance to testing ranged from 59 to 75 percent. Test sensitivity was highest in rehydrated samples, with 82 to 92 percent sensitivity for colorectal cancer or adenoma. Nonrehydrated samples had a sensitivity of 55 to 57 percent. Colorectal cancers were also detected earlier in the screening group. The positive predictive value of the fecal occult blood test (percentage of patients with a positive test who actually had cancer) ranged from 0.9 to 18.7 percent. Fecal occult blood testing did not reduce all-cause mortality.

Fecal occult blood testing is a cost-effective, noninvasive screening method for colon cancer. Although endoscopy has higher specificity for colorectal cancer, screening recommendations for colonoscopy and flexible sigmoidoscopy are based on case-control studies. In fact, there is no direct evidence that endoscopic screening reduces all-cause or colorectal cancer mortality.1 These tests also require more patient preparation and have a higher risk. Fecal occult blood testing remains a good screening option for average-risk, compliant patients.

Adenosine vs. Calcium Channel Blockers for Supraventricular Tachycardia

Clinical Question

How do the safety and effectiveness of adenosine (Adenocard) and calcium channel blockers compare in the treatment of supra-ventricular tachycardia?

Evidence-Based Answer

Adenosine and verapamil (Calan, Isoptin SR) are equally effective for treating acute supra-ventricular tachycardia in adults. Patients treated with adenosine have a higher rate of minor, transient adverse effects than patients treated with verapamil; however, rare but serious adverse effects may be more common with verapamil, especially in children. Although both agents are appropriate options, adenosine is generally the preferred initial agent.

Practice Pointers

Paroxysmal supraventricular tachycardia is usually caused by the development of a reentry circuit from anterograde and retrograde conduction through the atrioventricular node. In hemodynamically stable patients, initial management is focused on interrupting or modifying conduction in the atrioventricular node with vagal techniques (e.g., Valsalva maneuver, carotid artery massage, facial immersion in cold water). These techniques will terminate approximately 20 to 25 percent of episodes.1 If paroxysmal supra-ventricular tachycardia persists, adenosine and the nondihydropyridine calcium channel blockers verapamil and diltiazem (Cardizem) have been widely used for the condition.

This Cochrane review, which included eight studies and 577 total patients, found that adenosine and calcium channel blockers are equally effective in patients with paroxysmal supraventricular tachycardia. Only one study included children. Treatment groups in all studies were balanced in age and physiologic characteristics. However, most studies did not provide sufficient information about allocation concealment, blinding, and intention-to-treat analysis.

Minor adverse effects were more common in patients receiving adenosine, although the effects were typically short-lived. Conversely, major adverse effects, although uncommon, occurred only in patients treated with verapamil. These effects included two cardiac arrests (both occurred in children) and three episodes of hypotension.

Because of adenosine's rapid onset, short half-life, and favorable safety profile, the American College of Cardiology, American Heart Association (AHA), and European Society of Cardiology recommend adenosine as the preferred agent for the pharmacologic management of paroxysmal supraventricular tachycardia.2 The AHA Advanced Cardiac Life Support guideline recommends initially administering a 6-mg adenosine bolus over one to three seconds followed by a 20-mL saline flush.1 If this does not convert the rhythm, a 12-mg bolus should follow; a second 12-mg bolus may be given if the first is ineffective.1 Before adenosine is administered, patients should be counseled about the common adverse effects associated with the drug.

Nondihydropyridine calcium channel blockers should be second-line agents or used in patients with contraindications to adenosine. If the patient initially improves with adenosine therapy, but paroxysmal supraventricular tachycardia quickly returns, verapamil and diltiazem may be useful because of their longer half-lives. Ultimately, good clinical judgment based on the patient's characteristics, comorbidities, and preferences should guide the choice of agents.