HemeSelect and a combination of HemeSelect with Hemoccult II Sensa accurately screened for colorectal cancer
ACP J Club. 1996 May-June;124:74. doi:10.7326/ACPJC-1996-124-3-074
Allison JE, Tekawa IS, Ransom LJ, Adrain AL. A comparison of fecal occult-blood tests for colorectal-cancer screening. N Engl J Med. 1996 Jan 18;334:155-9. [PubMed ID: 8531970]
To determine the diagnostic accuracy of Hemoccult II, Hemoccult II Sensa, HemeSelect, and the combination of Hemoccult II Sensa and HemeSelect in screening for colorectal cancer.
Blinded comparison of the results of Hemoccult II, Hemoccult II Sensa, and HemeSelect with histopathologically confirmed colorectal neoplasms identified in the 2 years after screening.
Kaiser Permanente Medical Center in Oakland, California, USA.
8104 persons, aged ≥ 50 years (59% women), who received a personal health appraisal and consented to participate in a screening program for colorectal cancer. 96% of the patients completed a 2-year follow-up.
Description of Tests and Diagnostic Standard
For 1 week before the appraisal, participants were to follow a special diet, and 3 days before testing, they were to begin collecting specimens. 3 separate stool specimens were applied to 3 cards, each containing the 3 fecal occult-blood tests: Hemoccult II, Hemoccult II Sensa, and HemeSelect (SmithKline Diagnostics, San Jose, California). A positive Hemoccult II or Hemoccult II Sensa test was defined as one in which the blue color diffused into a 0.5-cm margin around the specimen within 1 minute after application of the developer. The absence of a blue color was interpreted as negative. Samples that showed agglutination at a dilution of 1:8 during HemeSelect testing were interpreted as positive. The absence of agglutination was interpreted as a negative test. The result of the combination test was considered positive when a positive Hemoccult II Sensa result was confirmed by a positive HemeSelect result. Test performance was evaluated by identifying patients who were found to have histopathologically confirmed neoplasms in the 2 years after screening.
Main Outcome Measures
Sensitivity and specificity.
At least 1 fecal occult-blood test was positive in 1312 patients (16%). Neoplasms were detected in 142 patients. Test characteristics for detecting carcinoma with Hemoccult II, the combination test, HemeSelect, and Hemoccult II Sensa, are displayed in the Table.
HemeSelect and a combination test of HemeSelect used to confirm positive Hemoccult II Sensa results were superior to Hemoccult II screening for colorectal cancer.
Sources of funding: Northern California Kaiser Foundation Hospitals Community Service Program and SmithKline Diagnostics.
For article reprint: Dr. J. E. Allison, Department of Medicine, Kaiser Permanente Medical Center, 280 West MacArthur Boulevard, Oakland, CA 94611-5693, USA. FAX 510-596-7017.
Table. Hemoccult II, Hemocult II Sensa, and HemeSelect alone and together for the diagnosis of colorectal cancer*
|Hemoccult II Sensa||79%||87%||6.08||0.24|
*LRs defined in Glossary and calculated from data in article.
Death from colorectal cancer can be prevented by screening with Hemoccult II (1), but this test is not particularly sensitive for cancer (although a series of yearly tests may overcome this drawback) and detects only large polyps at best. False-positive results are common, as many as 50 for every case of cancer detected, which leads to many diagnostic colonoscopies. We need a screening test that is more sensitive and more specific than Hemoccult II.
This study compared Hemoccult II with 2 alternative tests for fecal occult blood: Hemoccult II Sensa and HemeSelect. The authors studied a large, screened population but had to depend on an imperfect standard—2 years of follow-up—for the true presence or absence of colorectal neoplasm. To the extent that polyps and cancer present at the time of screening did not either cause a positive screening test or become symptomatic in that interval—and many would not—the study overestimated sensitivity. The authors found that Hemoccult II Sensa is more sensitive than Hemoccult II, but at the expense of specificity. HemeSelect, based on a different principle (it detects hemoglobin, not peroxidase activity), is not as sensitive as Hemoccult II Sensa but is almost as specific as Hemoccult II. Taking the cost of HemeSelect and its diagnostic accuracy into account, a combination test seems best: the most sensitive test (Hemoccult II Sensa) first; then the more specific test (HemeSelect) on those who test positive. HemeSelect, which is more expensive, would be needed only for a small proportion of the screened population. Most of the cost of colorectal cancer screening programs is in the diagnostic work-up of patients with false-positive screening results (2).
If the new screening test is truly more accurate than Hemoccult II, its effectiveness need not be confirmed by randomized controlled trials. Hemoccult II screening is known to save lives but can do so only by detecting neoplasms, thus triggering diagnostic work-up and treatment. This study does not provide enough evidence to change clinical policy, but it adds to the evidence that we can do better than screening with Hemoccult II alone.
Robert H. Fletcher, MD, MSc
Harvard Medical SchoolBoston, Massachusetts, USA