What drugs should be discontinued when preparing the patient for the analysis of feces for occult blood?

For a complete investigation, this test ideally requires three separate faeces specimens collected on three separate days.
If your doctor requests only one specimen, this can also be performed.
All specimens must be returned within five days of the first collection.
If you are taking iron tablets, you may continue this therapy before and during the test period.
Avoid alcohol and the following medications (Indomethacin, Reserpine, Phenylbutazone and Corticosteroids) as these may cause gastrointestinal irritation and subsequent bleeding in some patients. Consult your doctor before ceasing any medication.
Seven days prior to taking the sample, avoid Aspirin or anti- inflammatory drugs.
Two days prior to taking the sample, stop using rectal medicines and tonics.

You are menstruating
You have bleeding haemorrhoids
You are constipated
You have urinary bleeding
You have rectal bleeding

Equipment

3x Sample Tubes - Available from any Australian Clinical Labs Collection Centre or your doctor.

Write your surname, first given name, date of birth, sample number (if multiple specimens), and date and time of collection on the tube.
Collect faeces specimen into a clean container or onto toilet paper. Avoid contamination with toilet water.
Twist the cap on the sampler bottle to open. The sampling probe is attached to the cap.
Randomly insert the threaded end of the sampler into the faecal specimen in at least five different places on the specimen.
Insert sampling probe into the collection tube. Line up the cap with the tube and press to click shut.
Shake tube vigorously to mix specimen in fluid.
Place both sampler tubes (three tubes) into the plastic specimen bag provided.
Keep specimens refrigerated until returned to an Australian Clinical Labs Collection Centre.

Download instructions

Table of Contents Show

What are the types of fecal occult blood tests?
What should I avoid before a guaiac-based FOBT?
What should I avoid before an FIT?
When can I take this test?
How to collect your stool for this test?
What should I expect after the procedure?
Questions to ask your health care team
Related Resources
More Information

The collection staff are required to check your details (surname, first given name, date of birth and date and time of collection on the container label) against the pathology request form to ensure the sample is matched to the doctor’s request. This is done to ensure the safety and security of reporting your test results.

The fecal occult blood test (FOBT) is used to find blood in the feces, or stool. An FOBT finds blood in the stool that you cannot see. Blood in the stool may be a sign of colorectal cancer or another medical problem, such as an ulcer or polyps. Polyps are growths that develop on the inner wall of the colon and rectum.

FOBTs are one type of screening tool that doctors use to find colorectal cancer. Regular colorectal cancer screenings are recommended for people age 45 and older. If you have a family history of colorectal cancer or if you have other risk factors of developing colorectal cancer, your doctor may recommend that you start regular screening earlier. Learn more about the colorectal cancer risk factors.

What are the types of fecal occult blood tests?

There are 2 types of FOBTs, both of which you can do at home:

Guaiac-based FOBT. During the test, you place a stool sample on a test card coated with a plant-based substance called guaiac. The card changes color if there is blood in the stool. Then, you send the card back to your doctor's office or the lab for interpreting. Usually, this test is provided to you by your doctor's office or a laboratory.

Some guaiac-based FOBTs use flushable pads instead of a card. They are available without a prescription at many drugstores. Results are available to the user right away.

Fecal immunochemical test (FIT) or immunochemical FOBT. This test uses a specialized protein called an antibody. This specific protein attaches to hemoglobin, the oxygen-carrying part of red blood cells. A sample of the stool is placed in a tube or on a card and sent away to the doctor or laboratory for testing.

The immunochemical test has some benefits over the guaiac test. But both tests are used and can provide information about blood in the stool.

What should I avoid before a guaiac-based FOBT?

Before a guaiac-based FOBT, you cannot eat some foods or take certain medications. Some substances can cause the test to say there is blood in the stool when there is none. This is called a false-positive result.

If you will be taking the guaiac test, talk with your health care team about your diet and the medications you are taking. There are different tests available, and each one has different recommendations for what to avoid.

Most of the time, your health care provider will tell you to increase your fiber intake. You will also most likely need to avoid:

Certain vitamin supplements, such as vitamin C and iron
Rare red meat, like beef and lamb
Non-steroidal anti-inflammatory drugs (NSAIDs), like aspirin, ibuprofen, or naproxen
Blood-thinning medications

For some guaiac-based FOBTs, you will need to avoid certain fruits and vegetables. Ask your health care team or refer to the instructions on your FOBT to know what to avoid and for how long.

What should I avoid before an FIT?

Before an FIT, you do not need to make any dietary changes but you do need to avoid certain medications. NSAIDs and blood-thinning medications may change the results of your test. Your health care team will let you know what medications to avoid before taking the test.

When can I take this test?

Talk with your health care team about your medical conditions to decide the best timing for your FOBT. For example, the test should not be taken if you have bleeding hemorrhoids, peptic ulcers, or gastritis. You should also not take the test during your menstrual period. These can give a false-positive result.

How to collect your stool for this test?

Your health care provider will give you instructions for how to best collect the stool samples for your FOBT, whether you are doing a guaiac test or an immunochemical test. There are different brand names for FOBTs, and the instructions can vary for each one.

Guaiac-based FOBT. For a guaiac-based FOBT, you will need to collect 3 stool samples. Usually, these samples need to be collected in a clean container. This means that the sample is not mixed with urine or water from the toilet.

Your test package will include an applicator. Use the applicator to put a sample of your stools on the provided cards or slides. Package the cards as directed and mail them back to your health care provider or the laboratory.

Sometimes, the guaiac FOBT will be done with flushable wipes. After a bowel movement, drop the provided wipe into the toilet. The wipe will change color if blood is present in the stool. Record the results for 3 bowel movements and send the information to your health care provider.

FIT. For an FIT, you will need to collect 2 to 3 stool samples. This stool sample can be collected from the toilet using the applicator tool that was included in your kit. You will apply the sample to the container or card provided. Package the samples as directed and mail them to the laboratory.

What should I expect after the procedure?

You can resume your normal activities right after completing the FOBT. After learning the results, talk with your health care team about whether there are any next steps to take.

Questions to ask your health care team

Before having an FOBT, consider asking the following questions:

Why do you recommend this test for me?
What are the differences between the guaiac-based FOBT and the immunochemical FOBT? Which test do you recommend and why?
How often do I need to take this test?
What can I eat or drink before the test?
Should I avoid any foods or medications before the test?
How accurate is the FOBT in detecting blood in the stool?
How accurate is the FOBT in detecting polyps and colorectal cancer?
What is a false-positive result? What is a false-negative result?
When will my test results be ready? Who will explain the results to me?
Do you recommend having another test with the FOBT, such as a flexible sigmoidoscopy exam?
If the results indicate blood in the stool, will further tests, such as a colonoscopy, be necessary?

Cancer Screening

Guide to Colorectal Cancer

More Information

U.S. Centers for Disease Control and Prevention: Colorectal Cancer Screening Tests

1. US Preventive Services Task Force . Screening for colorectal cancer: US Preventive Services Task Force recommendation statement. Rockville, MD: US Preventive Services Task Force; 2008. Available from: www.uspreventiveservicestaskforce.org/uspstf/uspscolo.htm. Accessed 2011 Aug 1. [Google Scholar]

2. Canadian Cancer Society . Population-based colorectal cancer screening. Toronto, ON: Canadian Cancer Society; 2008. Available from: www.cancer.ca/Canada-wide/Prevention/Getting%20checked/Colorectal%20cancer%20screening.aspx?sc_lang=en. Accessed 2012 Aug 1. [Google Scholar]

3. Friedman LC, Webb JA, Richards CS, Plon SE. Psychological and behavioral factors associated with colorectal cancer screening among Ashkenazim. Prev Med. 1999;29(2):119–25. [PubMed] [Google Scholar]

4. Zapka JG, Puleo E, Vickers-Lahti M, Luckmann R. Healthcare system factors and colorectal cancer screening. Am J Prev Med. 2002;23(1):28–35. [PubMed] [Google Scholar]

5. Weitzman ER, Zapka J, Estabrook B, Goins KV. Risk and reluctance: understanding impediments to colorectal cancer screening. Prev Med. 2001;32(6):502–13. [PubMed] [Google Scholar]

6. Manne S, Markowitz A, Winawer S, Meropol NJ, Haller D, Rakowski W, et al. Correlates of colorectal cancer screening compliance and stage of adoption among siblings of individuals with early onset colorectal cancer. Health Psychol. 2002;21(1):3–15. [PubMed] [Google Scholar]

7. Brawarsky P, Brooks DR, Mucci LA. Correlates of colorectal cancer testing in Massachusetts men and women. Prev Med. 2003;36(6):659–68. [PubMed] [Google Scholar]

8. Brawarsky P, Brooks DR, Mucci LA, Wood PA. Effect of physician recommendation and patient adherence on rates of colorectal cancer testing. Cancer Detect Prev. 2004;28(4):260–8. [PubMed] [Google Scholar]

9. Brenes GA, Paskett ED. Predictors of stage of adoption for colorectal cancer screening. Prev Med. 2000;31(4):410–6. [PubMed] [Google Scholar]

10. Vernon SW. Participation in colorectal cancer screening: a review. J Natl Cancer Inst. 1997;89(19):1406–22. [PubMed] [Google Scholar]

11. Hoogewerf PE, Hislop TG, Morrison BJ, Burns SD, Sizto R. Health belief and compliance with screening for fecal occult blood. Soc Sci Med. 1990;30(6):721–6. [PubMed] [Google Scholar]

12. O’Malley AS, Beaton E, Yabroff KR, Abramson R, Mandelblatt J. Patient and provider barriers to colorectal cancer screening in the primary care safety-net. Prev Med. 2004;39(1):56–63. [PubMed] [Google Scholar]

13. Sangster JF, Gerace TM, Bass MJ. Hemoccult II screening for bowel cancer: will family practice patients accept it? Can Fam Physician. 1986;32:289–95. [PMC free article] [PubMed] [Google Scholar]

14. Dent OF, Bartrop R, Goulston KJ, Chapuis PH. Participation in faecal occult blood screening for colorectal cancer. Soc Sci Med. 1983;17(1):17–23. [PubMed] [Google Scholar]

15. Sewitch MJ, Fournier C, Ciampi A, Dyachenko A. Adherence to colorectal cancer screening guidelines in Canada. BMC Gastroenterol. 2007;7:39. [PMC free article] [PubMed] [Google Scholar]

16. Konrad G. Dietary interventions for fecal occult blood test screening: systematic review of the literature. Can Fam Physician. 2010;56:229–38. [PMC free article] [PubMed] [Google Scholar]

17. Rabeneck L, Zwaal C, Goodman JH, Mai V, Zamkanei M. Cancer care Ontario guaiac fecal occult blood test (FOBT) laboratory standards: evidentiary base and recommendations. Clin Biochem. 2008;41(16–17):1289–305. [PubMed] [Google Scholar]

18. Barada K, Abdul-Baki H, El H, 2nd, Hashash JG, Green PH. Gastrointestinal bleeding in the setting of anticoagulation and antiplatelet therapy. J Clin Gastroenterol. 2009;43(1):5–12. [PubMed] [Google Scholar]

19. Beckman Coulter . Hemoccult II® patient instructions. Fullerton, CA: Beckman Coulter; 2005. Available from: http://hemoccultfobt.com/patients/patients_HemoII_Pt_Instr.htm. Accessed 2011 Aug 1. [Google Scholar]

20. Beckman Coulter . Hemoccult II® SENSA® patient instructions. Fullerton, CA: Beckman Coulter; 2005. Available from: http://hemoccultfobt.com/patients/patients_HemoII_Sensa_Pt_Instr.htm. Accessed 2011 Aug 1. [Google Scholar]

21. Cenogenics . TRI-SLIDE insert. Morganville, NJ: Cenogenics; 2008. Available from: www.cenogenics.net/pdf/tri-slide-insert.pdf. Accessed 2011 Aug 1. [Google Scholar]

22. BC Biomedical Laboratories . A test for fecal occult blood. Surrey, BC: BC Biomedical Laboratories; 2007. Available from: www.bcbio.com/pdfs/INS007ColoscreenEnglish.pdf. Accessed 2011 Aug 1. [Google Scholar]

23. LifeLabs Medical Laboratory Services . Instructions for Hema-Screen II test card. Toronto, ON: LifeLabs; 2009. Available from: www.lifelabs.com/files/BC/patients/Stool-Occult_Blood_Hema-screen_Card.pdf. Accessed 2011 Aug 1. [Google Scholar]

24. Sharma VK, Vasudeva R, Howden CW. Colorectal cancer screening and surveillance practices by primary care physicians: results of a national survey. Am J Gastroenterol. 2000;95(6):1551–6. [PubMed] [Google Scholar]

25. Sharma VK, Corder FA, Fancher J, Howden CW. Survey of the opinions, knowledge, and practices of gastroenterologists regarding colorectal cancer screening and use of the fecal occult blood test. Am J Gastroenterol. 2000;95(12):3629–32. [PubMed] [Google Scholar]

26. Sharma VK, Corder FA, Raufman JP, Sharma P, Fennerty MB, Howden CW. Survey of internal medicine residents’ use of the fecal occult blood test and their understanding of colorectal cancer screening and surveillance. Am J Gastroenterol. 2000;95(8):2068–73. [PubMed] [Google Scholar]

27. Fries JF, Britton MC. Fenoprofen calcium in rheumatoid arthritis. A controlled double-blind crossover evaluation. Arthritis Rheum. 1973;16(5):629–34. [PubMed] [Google Scholar]

28. Greenberg PD, Cello JP, Rockey DC. Relationship of low-dose aspirin to GI injury and occult bleeding: a pilot study. Gastrointest Endosc. 1999;50(5):618–22. [PubMed] [Google Scholar]

29. Brooks CD, Schmid FR, Biundo J, Blau S, Gonzalez-Alcover R, Gowans JD, et al. Ibuprofen and aspirin in the treatment of rheumatoid arthritis. A cooperative double-blind trial. Rheumatol Phys Med. 1970;10(Suppl 10):10–63. [PubMed] [Google Scholar]

30. Zuin M, Podda M, Selmi C, Giorgini A, Zermiani P, Mandelli G, et al. Gastrointestinal tolerability of ibuprofen administered in two pharmaceutical formulations. Arzneimittelforschung. 2000;50(9):837–42. [PubMed] [Google Scholar]

31. Hurlen M, Eikvar L, Seljeflot I, Arnesen H. Occult bleeding in three different antithrombotic regimes after myocardial infarction. A WARIS-II subgroup analysis. Thromb Res. 2006;118(4):433–8. [PubMed] [Google Scholar]

32. Bahrt KM, Korman LY, Nashel DJ. Significance of a positive test for occult blood in stools of patients taking anti-inflammatory drugs. Arch Intern Med. 1984;144(11):2165–6. [PubMed] [Google Scholar]

33. Norfleet RG. 1,300 mg of aspirin daily does not cause positive fecal Hemoccult tests. J Clin Gastroenterol. 1983;5(2):123–5. [PubMed] [Google Scholar]

34. Greenberg PD, Cello JP, Rockey DC. Asymptomatic chronic gastrointestinal blood loss in patients taking aspirin or warfarin for cardiovascular disease. Am J Med. 1996;100(6):598–604. [PubMed] [Google Scholar]

35. Niv Y. Influence of non-steroidal anti-inflammatory drugs in faecal occult blood tests. Br Med J (Clin Res Ed) 1987;295(6595):446. [PMC free article] [PubMed] [Google Scholar]

36. Pye G, Ballantyne KC, Armitage NC, Hardcastle JD. Influence of nonsteroidal anti-inflammatory drugs on the outcome of faecal occult blood tests in screening for colorectal cancer. Br Med J (Clin Res Ed) 1987;294(6586):1510–1. [PMC free article] [PubMed] [Google Scholar]

37. Kahi CJ, Imperiale TF. Do aspirin and nonsteroidal anti-inflammatory drugs cause false-positive fecal occult blood test results? A prospective study in a cohort of veterans. Am J Med. 2004;117(11):837–41. [PubMed] [Google Scholar]

38. Clarke P, Jack F, Carey FA, Steele RJ. Medications with anticoagulant properties increase the likelihood of a negative colonoscopy in faecal occult blood test population screening. Colorectal Dis. 2006;8(5):389–92. [PubMed] [Google Scholar]

39. Sawhney MS, McDougall H, Nelson DB, Bond JH. Fecal occult blood test in patients on low-dose aspirin, warfarin, clopidogrel, or non-steroidal anti-inflammatory drugs. Dig Dis Sci. 2010;55(6):1637–42. [PubMed] [Google Scholar]

40. Doran J, Hardcastle JD. Bleeding patterns in colorectal cancer: the effect of aspirin and the implications for faecal occult blood testing. Br J Surg. 1982;69(12):711–3. [PubMed] [Google Scholar]

41. Kewenter J, Svanvik J, Svensson C, Wallgren K. The diagnostic value of the Hemoccult as a screening test in patients taking anticoagulants. Cancer. 1984;54(12):3054–8. [PubMed] [Google Scholar]

42. Jaffin BW, Bliss CM, LaMont JT. Significance of occult gastrointestinal bleeding during anticoagulation therapy. Am J Med. 1987;83(2):269–72. [PubMed] [Google Scholar]

43. Kershenbaum A, Lavi I, Rennert G, Almog R. Fecal occult blood test performance indicators in warfarin-treated patients. Dis Colon Rectum. 2010;53(2):224–9. [PubMed] [Google Scholar]

44. Bini EJ, Rajapaksa RC, Weinshel EH. Positive predictive value of fecal occult blood testing in persons taking warfarin. Am J Gastroenterol. 2005;100(7):1586–92. [PubMed] [Google Scholar]

45. Iles-Shih L, Collins JF, Holub JL, Lieberman DA. Prevalence of significant neoplasia in FOBT-positive patients on warfarin compared with those not on warfarin. Am J Gastroenterol. 2010;105(9):2030–5. [PMC free article] [PubMed] [Google Scholar]

46. Lifton LJ, Kreiser J. False-positive stool occult blood tests caused by iron preparations. A controlled study and review of literature. Gastroenterology. 1982;83(4):860–3. [PubMed] [Google Scholar]

47. Kulbaski MJ, Goold SD, Tecce MA, Friedenheim RE, Palarski JD, Brancati FL. Oral iron and the Hemoccult test: a controversy on the teaching wards. N Engl J Med. 1989;320(22):1500. [PubMed] [Google Scholar]

48. McDonnell WM, Ryan JA, Seeger DM, Elta GH. Effect of iron on the guaiac reaction. Gastroenterology. 1989;96(1):74–8. [PubMed] [Google Scholar]

49. Ahlquist DA, McGill DB, Schwartz S, Taylor WF, Owen RA. Fecal blood levels in health and disease. A study using HemoQuant. N Engl J Med. 1985;312(22):1422–8. [PubMed] [Google Scholar]

50. Morris DW, Hansell JR, Ostrow JD, Lee CS. Reliability of chemical tests for fecal occult blood in hospitalized patients. Am J Dig Dis. 1976;21(10):845–52. [PubMed] [Google Scholar]

51. Laine LA, Bentley E, Chandrasoma P. Effect of oral iron therapy on the upper gastrointestinal tract. A prospective evaluation. Dig Dis Sci. 1988;33(2):172–7. [PubMed] [Google Scholar]

52. Eliakim R, Fich A, Mor-Yosef S, Granot E. Effect of different iron preparations on various tests for occult blood in feces. Isr J Med Sci. 1988;24(6):328–9. [PubMed] [Google Scholar]

53. Coles EF, Starnes EC. Use of HemoQuant assays to assess the effect of oral iron preparations on stool Hemoccult tests. Am J Gastroenterol. 1991;86(10):1442–4. [PubMed] [Google Scholar]

54. Anderson GD, Yuellig TR, Krone RE., Jr An investigation into the effects of oral iron supplementation on in vivo Hemoccult stool testing. Am J Gastroenterol. 1990;85(5):558–61. [PubMed] [Google Scholar]

55. Jaffe RM, Kasten B, Young DS, MacLowry JD. False-negative stool occult blood tests caused by ingestion of ascorbic acid (vitamin C) Ann Intern Med. 1975;83(6):824–6. [PubMed] [Google Scholar]

56. Jaffe RM, Zierdt W. A new occult blood test not subject to false-negative results from reducing substances. J Lab Clin Med. 1979;93(5):879–86. [PubMed] [Google Scholar]

57. Zierdt WS, Zierdt CH. Occult blood testing using tetramethylbenzidine in an extraction procedure for patients on unrestricted diets. Am J Clin Pathol. 1985;83(4):486–8. [PubMed] [Google Scholar]

58. Mandel JS, Church TR, Bond JH, Ederer F, Geisser MS, Mongin SJ, et al. The effect of fecal occult-blood screening on the incidence of colorectal cancer. N Engl J Med. 2000;343(22):1603–7. [PubMed] [Google Scholar]

59. Tunget CL, Clark RF, Manoguerra AS, Turchen SG. Iron overdose and detection of gastrointestinal bleeding with the Hemoccult and Gastroccult assays. Ann Emerg Med. 1995;26(1):54–7. [PubMed] [Google Scholar]

60. Barrett JF. Effect of ascorbic acid on the chemical tests for blood. Lancet. 1936;228(5908):1214. [Google Scholar]

61. Garrick DP, Close JR, McMurray W. Detection of occult blood in faeces. Lancet. 1977;2(8042):820–1. [PubMed] [Google Scholar]

62. Gogel HK, Tandberg D, Strickland RG. Substances that interfere with guaiac card tests: implications for gastric aspirate testing. Am J Emerg Med. 1989;7(5):474–80. [PubMed] [Google Scholar]

63. Imperiale TF. Continue or discontinue warfarin for fecal occult blood testing in 2010? Does the published evidence provide an answer? Am J Gastroenterol. 2010;105(9):2036–9. [PubMed] [Google Scholar]

64. Rose IS, Young GP, St John DJ, Deacon MC, Blake D, Henderson RW. Effect of ingestion of hemoproteins on fecal excretion of hemes and porphyrins. Clin Chem. 1989;35(12):2290–6. [PubMed] [Google Scholar]

65. Levi Z, Rozen P, Hazazi R, Vilkin A, Waked A, Maoz E, et al. Sensitivity, but not specificity, of a quantitative immunochemical fecal occult blood test for neoplasia is slightly increased by the use of low-dose aspirin, NSAIDs, and anticoagulants. Am J Gastroenterol. 2009;104(4):933–8. [PubMed] [Google Scholar]

66. Chieffi M, Kirk JE. The ascorbic acid excretion in the stool in elderly subjects. J Nutr. 1956;59(2):273–6. [PubMed] [Google Scholar]

Page 2

Studies examining FOBT and NSAIDs and anticoagulant medications

STUDY	STUDY POPULATION	STUDY GROUPS	DESIGN	RESULTS	COMMENTS
Fries and Britton (1973)27	Rheumatoid arthritis (N = 27) (mean age 56.3 y)	Fenoprofen (1.4–2.4 g/d) for 6 wkHigh-dose ASA (4–6 g/d) for 6 wk Placebo for 3 wk	RCT, double-blind crossover with temporal controls	Placebo: 15.4% positive FOBT resultsASA: 17.1% positive resultsFenoprofen: 20% positive results No significant difference between groups	Unspecified guaiac-based FOBT; true positives not determined
Greenberg et al (1999)28	Healthy house officer volunteers (mean age 29.8 y)	ASA (30, 81, or 325 mg/d) for 30 d (n = 10 in each group) Placebo for 30 d (n = 10)	RCT, double blind	0 positive results using Hemoccult II or Hemoccult SENSA, in all groups
Brooks et al (1970a)29	Rheumatoid arthritis (mean age 51.5 y)	Ibuprofen (600 mg/d) for 4 wk (n = 41)ASA (3.6 g/d) for 4 wk (n = 45) U-24568 (600 mg/d) for 4 wk (n = 41)	Randomized, double blind	Total positive FOBT results not clarified No significant differences between groups	No control group; unspecified guaiac-based FOBT
Brooks et al (1970b)29	Rheumatoid arthritis (mean age 53.1 y)	Ibuprofen (900 mg/d) for 4 wk (n = 60) ASA (3.6 g/d) for 4 wk (n = 62)	Randomized, double blind	Total positive FOBT results not clarified No significant differences between groups	No control group; unspecified guaiac-based FOBT
Zuin et al (2000)30	Healthy volunteers (mean age 27.7 y)	Ibuprofen tablet (800 mg/d) for 7 d (n = 18) Ibuprofen fast-melting tablets (800 mg/d) for 7 d (n = 18)	Two-sequence crossover	0 positive FOBT results	No control group; unspecified FOBT
Hurlen et al (2006)31	AMI survivors (mean age 60.9 y)	ASA (160 mg/d) for 3 mo (n = 94) Warfarin (INR 2.8–4.2) for 3 mo (n = 84) ASA (75 mg/d) plus warfarin (INR 2.0–2.5) for 3 mo (n = 89)	Randomized	ASA: 8.5% positive hemo FEC resultsWarfarin: 7.1% positive resultsASA with warfarin: 5.6% positive results No significant differences between groups	No control group; 14 of 19 positive results retested (3 remained positive, 2 with diverticulosis and 1 with normal findings on colonoscopy)
Bahrt et al (1984)32	Rheumatoid disease clinic patients (age not reported)	Unspecified NSAID, salicylate, or steroid use (n = 145)	Cross-sectional	Anti-inflammatory: 5.5% positive results using Hemoccult	No control group; all positive results evaluated (2 colonic neoplasms [PPV 25%])
Norfleet (1983)33	Healthy volunteers (N = 27)	Control period for 3 d ASA (1300 mg/d) for 7 d	Temporally controlled trial	0 positive Hemoccult II test results during both test periods
Greenberg et al (1996)34	Medical, cardiac, and anticoagulation clinic patients (mean age approximately 60 y)	Control for 1 wk, then ASA 325 mg/d for 8 wk (n = 25)ASA 325 mg/d for 1 wk, then ASA 81 mg/d for 8 wk (n = 46)ASA 81 mg/d for 1 wk, then ASA 325 mg/d for 8 wk (n = 4) Warfarin (unspecified INR) for 4–6 wk (n = 25)	Cross-sectional with crossover	Control week: 0 positive results using Hemoccult IIASA 81 mg/d: 14% positive resultsASA 325 mg/d: 4% positive resultsWarfarin: 12% positive results No significant differences between groups	Blood loss quantified with HemoQuant; no difference between groups
Niv (1987)35	Israeli screening population taking NSAIDs (aged > 40 y)	Self-reported discontinuing NSAIDs during FOBT (n = 1771) Self-reported NSAID use during FOBT (n = 26)	Cohort	NSAID users: 27% positive results using Hemoccult II Nonusers: 4% positive results (P < .01)	Relied on self-reporting of compliance with FOBT instructions
Pye et al (1987)36	Asymptomatic subjects with positive screening results on Hemoccult or Feca-EIA (aged 50–74 y)	NSAID use according to self-report (n = 50) No NSAID use according to self-report (n = 405)	Cross-sectional	4.2% total positive Hemoccult or Feca-EIA results from screening population of 10 931 All positive results evaluated with colonoscopyNSAID users: PPV 20% for neoplasiaNonusers: PPV 32% No significant difference (P = .1)	Hemoccult and Feca-EIA (immunologic test) results not reported separately
Kahi and Imperiale (2004)37	VA patients referred for colonoscopy with positive Hemoccult II FOBT results (N = 193) (mean age 66 y)	ASA or NSAID use according to self-report and record review (n = 135) No ASA or NSAID use according to self-report and record review (n = 58)	Cross-sectional	ASA or NSAID users: PPV 21% for “abnormality”Nonusers: PPV 19% No significant differences between groups	No correlation between ASA dose and colonoscopic pathology; not a screening population; large polyps and CRC were not reported separately from other colonic pathology
Clarke et al (2006)38	Scottish patients referred for colonoscopy with positive Hema Screen (guaiac) FOBT results (aged 50–69 y)	Self reported ASA, NSAID, or anticoagulant use (n = 301) No ASA, NSAID, or anticoagulant use (n = 308)	Cross-sectional	ASA, NSAID, or anticoagulant users: PPV 47.5% for colorectal neoplasia Nonusers: PPV 56.5% (P = .012)	PPV for CRC with no significant differences between groups (P = .7); anticoagulants made up only 7.7% of prescriptions
Sawhney et al (2010)39	VA patients referred for colonoscopy with positive Hemoccult II results (mean age approximately 68 y)	No medications according to review of pharmacy profile (n = 518)ASA (n = 264)NSAIDs (n = 218) Warfarin (n = 85) Clopidogrel (n = 41)	Cross-sectional	Controls: PPV 30.5% for advanced neoplasia ASA users: PPV 20.5% (P < .01) NSAID users: PPV 19.7% (P < .01) Warfarin users: PPV 20% (P = .05) Clopidogrel users: PPV 7.3% (P < .01)	Not a screening population; included positive FOBT results for evaluation of symptoms
Doran and Hardcastle (1982)40	CRC patients and age-matched controls	Temporal control without ASA, then ASA (600 mg/d) for 3 d (n = 50) Age-matched subjects with temporal control, then ASA (600 mg/d) for 3 d (n = 50)	Temporally controlled trial with control cohort component	CRC patients during temporal control: 70% positive Hemoccult II results CRC patients taking ASA: 82% positive results (P = .07) Age-matched cohort: single subject with positive Hemoccult II results before and while taking ASA	51Cr-RBC labeling in CRC patients (n = 25) showed no correlation between blood volume and ASA use or tumour location
Kewenter et al (1984)41	Patients taking dicumarol (N = 849) (mean age 67 y)	Dicumarol, unspecified dose	Cross-sectional	15% positive results using Hemoccult II PPV 19% for CRC and adenomas among 79 subjects evaluated further (57 of 67 with ≥ 3 of 6 positive samples; 22 of 61 with < 3 of 6 positive samples)	No correlation between positive Hemoccult result and anticoagulation index
Jaffin et al (1987)42	Patients taking warfarin, heparin, or both (n = 256) and age- and diagnosis-matched inpatient controls (n = 164) (mean age 64 y)	Anticoagulant users (Hemoccult completed in n = 175) Age- and diagnosis-matched controls (Hemoccult completed in n = 74)	Controlled cross-sectional	Anticoagulant users: 12% positive results using Hemoccult Controls: 3% positive results (P < .01)	No correlation with anticoagulation index; evaluation of 16 of 21 positive test results among anticoagulant users (2 with CRC [PPV 12.5%]); no evaluation of positive test results in control group
Kershenbaum et al (2010)43	Israeli CRC screening program participants (aged 50–74 y)	Warfarin treatment (n = 1356 FOBTs) No antithrombotic or anticoagulant use (n = 64 088 FOBTs)	Cohort	Warfarin users: 7.7% positive results using Hemoccult SENSA Nonusers: 3.6% positive results (P < .01)Warfarin users: PPV 19.8% for CRC or clinically significant adenoma in 81.9% of positive FOBT resultsNonusers: PPV 27.7% in 74.7% of positive FOBT results No significant difference in PPV between groups
Bini et al (2005)44	Patients referred for colonoscopy to evaluate positive Hemoccult II results (mean age 72 y)	Warfarin users (n = 210) Age- and sex-matched controls (n = 210)	Controlled, cross-sectional	Warfarin users: PPV 27.2% for CRC or adenomasNonusers: PPV 24.3% for CRC or adenomas No significant difference in PPV between groups (P = .58)	Not a screening population; included positive FOBT results obtained for evaluation of symptoms
Iles-Shih et al (2010)45	Patients referred for colonoscopy to evaluate positive screening results using Hemoccult II (aged < 50 to > 80y)	Warfarin users (n = 372) Warfarin nonusers (n = 9265)	Cross-sectional	Warfarin users: PPV 16.1% for large polyps or tumoursNonusers: PPV 11.4% No significant difference in PPV between groups after adjusting for age and sex	INRs not reported