BACK TOTOP Browse A-ZSearchBrowse A-ZABCDEFGHIJKLMNOPQRSTUVWXYZ0-9 E-mail FormEmail ResultsName:Email address:Recipients Name:Recipients address:Message: Print-FriendlyBookmarksbookmarks-menuStool guaiac testColon cancer - guaiac test; Colorectal cancer - guaiac test; gFOBT; Guaiac smear test; Fecal occult blood test - guaiac smear; Stool occult blood test - guaiac smearThe stool guaiac test looks for hidden (occult) blood in a stool sample. It can find blood even if you cannot see it yourself. It is a common type of fecal occult blood test (FOBT).Guaiac is a substance from a plant that is used to coat the FOBT test cards to make them able to detect blood. How the Test is Performed Usually, you collect a small sample of stool at home. Sometimes, your health care provider may collect a small amount of stool from you during a rectal exam.If the test is done at home, you will use a test kit. Follow the kit instructions exactly. This ensures accurate results. In brief:You collect 2 stool samples from 3 different bowel movements. For each bowel movement, you sample 2 areas for each sample, and smear each sample in 1 of 2 places on a card provided in the kit. You mail the card to a laboratory for testing.Be sure to keep the stool away from any urine. Mixing of urine and stool can spoil the sample. How to Prepare for the Test Some foods can affect test results. Follow instructions about not eating certain foods before the test. These may include:Red meat Cantaloupe Uncooked broccoli Turnip Radish HorseradishSome medicines may interfere with the test. These include vitamin C, aspirin, and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen. Ask your provider if you need to stop taking these before the test. Never stop or change your medicine without first talking to your provider. In particular, high amounts of vitamin C for 3 days before the test could cause a false negative. How the Test will Feel The at-home test involves a normal bowel movement. There is no discomfort. You may have some discomfort if the stool is collected during a rectal exam. Why the Test is Performed This test detects blood in the digestive tract. It may be done if:You are being screened or tested for colon cancer. Colon cancerColorectal cancer is cancer that starts in the large intestine (colon) or the rectum (end of the colon). It is also sometimes simply called colon ca...ImageRead Article Now Book Mark Article You have abdominal pain, changes in bowel movements, or weight loss. You have anemia (low blood count). AnemiaAnemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. Different type...ImageRead Article Now Book Mark Article You say you have blood in the stool or black, tarry stools.Black, tarry stoolsBlack or tarry stools with a foul smell are a sign of a problem in the upper digestive tract. It most often indicates that there is bleeding in the ...ImageRead Article Now Book Mark Article Normal Results A negative test result means that there is no blood in the stool. Occasionally, this test will miss very small amounts of blood in the stool that is below the level of detection of this test (false negative). What Abnormal Results Mean Abnormal results may be due to any problem that causes bleeding in the stomach or intestinal tract, including:Swollen, fragile blood vessels in the colon that may result in blood loss Colon cancer Colon polyps Colon polypsA colorectal polyp is a growth on the lining of the colon or rectum.ImageRead Article Now Book Mark Article Enlarged veins, called varices, in the walls of the esophagus (the tube that connects your throat to your stomach) that bleed VaricesThe esophagus (food pipe) is the tube that connects your throat to your stomach. Varices are enlarged veins that may be found in the esophagus in pe...ImageRead Article Now Book Mark Article Inflamed or swollen lining of the stomach or the esophagus Infections in the stomach or intestines Hemorrhoids HemorrhoidsHemorrhoids are swollen veins in the anus or lower part of the rectum.ImageRead Article Now Book Mark Article Crohn disease or ulcerative colitis Crohn diseaseCrohn disease is a disease where parts of the digestive tract become inflamed. It most often involves the lower end of the small intestine and the be...ImageRead Article Now Book Mark Article Ulcerative colitisUlcerative colitis is a condition in which the lining of the large intestine (colon) and rectum become inflamed. It is a form of inflammatory bowel ...ImageRead Article Now Book Mark Article Ulcer in the stomach or first part of the intestinesUlcer in the stomach or first part of t...A peptic ulcer is an open sore or raw area in the lining of the stomach (gastric ulcer) or in the first part of the small intestine (duodenal ulcer)....ImageRead Article Now Book Mark Article Other causes of a positive test, which do not indicate a problem in the gastrointestinal tract, include:Coughing up and then swallowing blood Nose bleedNose bleedA nosebleed is loss of blood from the tissue lining the nose. Bleeding most often occurs from one nostril only.ImageRead Article Now Book Mark Article If the stool guaiac results come back positive for blood in the stool, your provider will likely recommend other tests, often including a colonoscopy.ColonoscopyA colonoscopy is an exam that views the inside of the colon (large intestine) and rectum, using a tool called a colonoscope. The colonoscope has a sm...ImageRead Article Now Book Mark Article The stool guaiac test does not diagnose cancer. Screening tests such as colonoscopy can help detect cancer. The stool guaiac test and other screenings can catch colon cancer early, when it is easier to treat. Risks There can be false-positive and false-negative results. Errors are reduced when you follow instructions during collection and avoid certain foods and medicines.Note that the guaiac test is done less often these days. There is a more sensitive test to detect blood that needs only 1 sample and doesn't need any medication or food adjustments. This test is called FIT testing (fecal immunochemical testing).Open ReferencesReferencesde Kanter C, Dhaliwal S, Hawks M. Colorectal cancer screening: updated guidelines from the American College of Gastroenterology. Am Fam Physician. 2022;105(3):327-329. PMID: 335289558 pubmed.ncbi.nlm.nih.gov/35289558/.Lawler M, Johnston B, Van Schaeybroeck S, et al. Colorectal cancer. In: Niederhuber JE, Armitage JO, Kastan MB, Doroshow JH, Tepper JE, eds. Abeloff's Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:chap 74.National Cancer Institute website. Colorectal cancer prevention (PDQ) - health professional version. www.cancer.gov/types/colorectal/hp/colorectal-prevention-pdq. Updated April 11, 2025. Accessed July 11, 2025.National Comprehensive Cancer Network website. NCCN clinical practice guidelines in oncology (NCCN guidelines): colorectal cancer screening. Version 2.2025 - June 24, 2025. www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf. Updated June 24, 2025. Accessed July 11, 2025.Patel SG, May FP, Anderson JC, et al. Updates on age to start and stop colorectal cancer screening: recommendations from the U.S. Multi-Society Task Force on colorectal cancer. Gastroenterology. 2022;162(1):285-299. PMID: 34794816 pubmed.ncbi.nlm.nih.gov/34794816/.Savides TJ, Jensen DM. Gastrointestinal bleeding. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 20.US Preventive Services Task Force website. Final recommendation statement. Colorectal cancer: screening. www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening. Published May 18, 2021. Accessed April 2, 2025.AllVideoImagesTogFecal occult blood test - illustration A fecal occult blood test is a noninvasive test that detects the presence of hidden blood in the stool. Blood in the stool that is not visible is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer. Fecal occult blood testillustrationFecal occult blood test - illustration A fecal occult blood test is a noninvasive test that detects the presence of hidden blood in the stool. Blood in the stool that is not visible is often the first, and in many cases the only, warning sign that a person has colorectal disease, including colon cancer. Fecal occult blood testillustration Tests for Stool guaiac test Stool guaiac testRelated Information Colorectal polyps(Condition)Colorectal cancer(Condition)Tumor(Condition)Esophagitis(Condition)Gastritis(Condition)Hemorrhoids(Condition)Crohn disease(Condition)Peptic ulcer(Condition)Bleeding esophageal varices(Condition)Colon and rectal cancers - InDepth(In-Depth)Crohn disease - InDepth(In-Depth)Peptic ulcers - InDepth(In-Depth) Review Date: 1/30/2025 Reviewed By: Jenifer K. Lehrer, MD, Gastroenterologist, Philadelphia, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 07/11/2025. 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Stool guaiac testColon cancer - guaiac test; Colorectal cancer - guaiac test; gFOBT; Guaiac smear test; Fecal occult blood test - guaiac smear; Stool occult blood test - guaiac smearThe stool guaiac test looks for hidden (occult) blood in a stool sample. It can find blood even if you cannot see it yourself. It is a common type of fecal occult blood test (FOBT).Guaiac is a substance from a plant that is used to coat the FOBT test cards to make them able to detect blood. How the Test is Performed Usually, you collect a small sample of stool at home. Sometimes, your health care provider may collect a small amount of stool from you during a rectal exam.If the test is done at home, you will use a test kit. Follow the kit instructions exactly. This ensures accurate results. In brief:You collect 2 stool samples from 3 different bowel movements. For each bowel movement, you sample 2 areas for each sample, and smear each sample in 1 of 2 places on a card provided in the kit. You mail the card to a laboratory for testing.Be sure to keep the stool away from any urine. Mixing of urine and stool can spoil the sample. How to Prepare for the Test Some foods can affect test results. Follow instructions about not eating certain foods before the test. These may include:Red meat Cantaloupe Uncooked broccoli Turnip Radish HorseradishSome medicines may interfere with the test. These include vitamin C, aspirin, and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen. Ask your provider if you need to stop taking these before the test. Never stop or change your medicine without first talking to your provider. In particular, high amounts of vitamin C for 3 days before the test could cause a false negative. How the Test will Feel The at-home test involves a normal bowel movement. There is no discomfort. You may have some discomfort if the stool is collected during a rectal exam. Why the Test is Performed This test detects blood in the digestive tract. It may be done if:You are being screened or tested for colon cancer. Colon cancerColorectal cancer is cancer that starts in the large intestine (colon) or the rectum (end of the colon). It is also sometimes simply called colon ca...ImageRead Article Now Book Mark Article You have abdominal pain, changes in bowel movements, or weight loss. You have anemia (low blood count). AnemiaAnemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. Different type...ImageRead Article Now Book Mark Article You say you have blood in the stool or black, tarry stools.Black, tarry stoolsBlack or tarry stools with a foul smell are a sign of a problem in the upper digestive tract. It most often indicates that there is bleeding in the ...ImageRead Article Now Book Mark Article Normal Results A negative test result means that there is no blood in the stool. Occasionally, this test will miss very small amounts of blood in the stool that is below the level of detection of this test (false negative). What Abnormal Results Mean Abnormal results may be due to any problem that causes bleeding in the stomach or intestinal tract, including:Swollen, fragile blood vessels in the colon that may result in blood loss Colon cancer Colon polyps Colon polypsA colorectal polyp is a growth on the lining of the colon or rectum.ImageRead Article Now Book Mark Article Enlarged veins, called varices, in the walls of the esophagus (the tube that connects your throat to your stomach) that bleed VaricesThe esophagus (food pipe) is the tube that connects your throat to your stomach. Varices are enlarged veins that may be found in the esophagus in pe...ImageRead Article Now Book Mark Article Inflamed or swollen lining of the stomach or the esophagus Infections in the stomach or intestines Hemorrhoids HemorrhoidsHemorrhoids are swollen veins in the anus or lower part of the rectum.ImageRead Article Now Book Mark Article Crohn disease or ulcerative colitis Crohn diseaseCrohn disease is a disease where parts of the digestive tract become inflamed. It most often involves the lower end of the small intestine and the be...ImageRead Article Now Book Mark Article Ulcerative colitisUlcerative colitis is a condition in which the lining of the large intestine (colon) and rectum become inflamed. It is a form of inflammatory bowel ...ImageRead Article Now Book Mark Article Ulcer in the stomach or first part of the intestinesUlcer in the stomach or first part of t...A peptic ulcer is an open sore or raw area in the lining of the stomach (gastric ulcer) or in the first part of the small intestine (duodenal ulcer)....ImageRead Article Now Book Mark Article Other causes of a positive test, which do not indicate a problem in the gastrointestinal tract, include:Coughing up and then swallowing blood Nose bleedNose bleedA nosebleed is loss of blood from the tissue lining the nose. Bleeding most often occurs from one nostril only.ImageRead Article Now Book Mark Article If the stool guaiac results come back positive for blood in the stool, your provider will likely recommend other tests, often including a colonoscopy.ColonoscopyA colonoscopy is an exam that views the inside of the colon (large intestine) and rectum, using a tool called a colonoscope. The colonoscope has a sm...ImageRead Article Now Book Mark Article The stool guaiac test does not diagnose cancer. Screening tests such as colonoscopy can help detect cancer. The stool guaiac test and other screenings can catch colon cancer early, when it is easier to treat. Risks There can be false-positive and false-negative results. Errors are reduced when you follow instructions during collection and avoid certain foods and medicines.Note that the guaiac test is done less often these days. There is a more sensitive test to detect blood that needs only 1 sample and doesn't need any medication or food adjustments. This test is called FIT testing (fecal immunochemical testing).Open ReferencesReferencesde Kanter C, Dhaliwal S, Hawks M. Colorectal cancer screening: updated guidelines from the American College of Gastroenterology. Am Fam Physician. 2022;105(3):327-329. PMID: 335289558 pubmed.ncbi.nlm.nih.gov/35289558/.Lawler M, Johnston B, Van Schaeybroeck S, et al. Colorectal cancer. In: Niederhuber JE, Armitage JO, Kastan MB, Doroshow JH, Tepper JE, eds. Abeloff's Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:chap 74.National Cancer Institute website. Colorectal cancer prevention (PDQ) - health professional version. www.cancer.gov/types/colorectal/hp/colorectal-prevention-pdq. Updated April 11, 2025. Accessed July 11, 2025.National Comprehensive Cancer Network website. NCCN clinical practice guidelines in oncology (NCCN guidelines): colorectal cancer screening. Version 2.2025 - June 24, 2025. www.nccn.org/professionals/physician_gls/pdf/colorectal_screening.pdf. Updated June 24, 2025. Accessed July 11, 2025.Patel SG, May FP, Anderson JC, et al. Updates on age to start and stop colorectal cancer screening: recommendations from the U.S. Multi-Society Task Force on colorectal cancer. Gastroenterology. 2022;162(1):285-299. PMID: 34794816 pubmed.ncbi.nlm.nih.gov/34794816/.Savides TJ, Jensen DM. Gastrointestinal bleeding. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 11th ed. Philadelphia, PA: Elsevier; 2021:chap 20.US Preventive Services Task Force website. Final recommendation statement. Colorectal cancer: screening. www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening. Published May 18, 2021. Accessed April 2, 2025.
