Stool tests are done to find a cause of unexplained chronic or heavy acute diarrhea, anemia or weight loss. Tests may reveal intestinal parasites, bacterial infection, celiac disease or Crohn’s disease, blood and various substances (fats, reducing substances) that speak for intestinal malabsorption.
How to Prepare for a Stool Test?
1-2 weeks before the test, you should avoid antacids, anti-diarrheal and anti-parasite medications, antibiotics, enemas and laxatives (after discussion with your doctor). Your doctor can provide you a stool collection kit with instructions for its use. Emptying the bladder before having a bowel movement is recommended, so urine does not contaminate the stool.
Stool for the test should be collected in a plastic bag put over the toilet, or from a diaper, stored in a clean sealable container and taken to the laboratory within 1 hour or according to doctor’s instructions. In the lab, only stool tests, specifically ordered by the doctor, and not all possible tests, will be done. Beside specific tests, the stool will be checked for color, consistency, weight (volume), shape, odor, and the presence of mucus.
Stool culture can show harmful bacteria, like shigella or salmonella. For diagnosis of certain rare bacteria, like Vibrio cholerae, separate tests may be required. False positive results are due to contamination of stool sample with urine or blood, or due to more than an hour passed between sample taking and testing. False negative results may be from antibiotics, laxatives, anti-diarrheal drugs, or recent barium or x-ray investigation.
Other tests to detect gastrointestinal microbes include:
- Helycobacter pylori antigen (from the stomach) may be found in chronic upper abdominal bloating or in peptic ulcus.
- Clostridium difficile toxin test is recommended in diarrhea that appear during or after antibiotic treatment (antibiotic associated diarrhea).
- Rotavirus antigen may be searched in doubtful cases of acute diarrhea in small children.
Ova and Parasites (O&P)
Ova and parasites (O&P) test is recommended, when diarrhea lasts more than a week. Specific antigen tests for giardia, cryptosporidium and Entameba histolytica exist. Read about human intestinal parasites and intestinal worms.
Fecal Occult Blood Test (FOBT)
Fecal occult blood test (Hemoccult) should be done in unexplained anemia and when intestinal bleeding is suspected. Causes of blood in your stool.
WBC Stool Test
White blood cells in the stool may be found in severe bacterial infection, Crohn’s disease or ulcerative colitis.
Lactoferrin is released from leukocytes and it can be detected in the stool in 5 minutes. Increased lactoferrin is a sign of inflammation so it is checked in acute diarrhea to distinguish between mild viral or parasitic infection (negative) and invasive bacteria (positive), and in chronic diarrhea to distinguish between irritable bowel syndrome – IBS (negative) and inflammatory bowel disease -IBD (positive). In later case, lactoferrin test was found to be 86% sensitive and 100% specific (1,2). Calprotein is another leukocyte protein excreted in stool and correlates with activity of IBD (3). Fecal A1AT test detects serum protein alpha1-antitrypsin in the stool in the protein losing enteropathy (PLE). Radionuclide labeled proteins, injected into a vein, and then appearing in the stool, also speak for PLE. Tests for proteins, excreted in colorectal cancer, are still in the research phase. Protein CD23 was found in the stool of patients with a food allergy (4).
Fecal IgA Antibodies
Fecal IgA antibodies may be found in certain food allergies (to milk, egg, soy). In one clinical trial, IgA antigliadin antibodies in the stool were found in only 30% of patients with celiac disease, so they were considered as useless for its diagnosis (5).
Blood tests are recommended when gastrointestinal inflammation, infection, food allergies or poisoning are suspected.
How to Prepare?
Do not eat overnight before the test.
Chem-20 (Metabolic Panel 20)
Total proteins are lowered in protein loosing enteropathy, marasmus and kwashiorkor; glucose is elevated in diabetes; sodium and potassium are usually lowered in dehydration; bilirubin and liver enzymes are elevated in liver or biliary tract disease (6).
Red blood cells (RBC) (and ferritin, folate or vitamin B12) may be lowered in parasites, celiac and Crohn’s disease. White blood cells (WBC) are usually elevated in gastrointestinal infection or inflammation. Eosinophils (a type of white blood cells) are commonly elevated in food allergies and intestinal parasites.
Erythrocyte Sedimentation Rate (ESR) is usually elevated in ulcerative colitis and Crohn’s disease and reflects the activity of inflammation in the colon (but not in the small intestine); the test is used to evaluate a response to therapy (3). ESR may be also elevated in advanced colorectal cancer and carcinoid.
C-Reactive Protein (CRP) may be elevated in acute phases of Crohn’s disease or ulcerative colitis (3).
IgE and pANCA/ASCA Antibodies
- IgE antibodies may be elevated in food allergies and parasites; specific IgA and IgG antibodies may be elevated in celiac disease, Crohn’s disease, hepatitis, autoimmune diseases (SLE, systemic sclerosis, autoimmune thyroiditis), AIDS, Herpes simplex virus, cytomegalovirus or tuberculosis.
- The combination of serum antibodies pANCA and ASCA is used to distinguish between ulcerative colitis (UC) and Crohn’s disease (CD). Combination pANCA+/ASCA- was found 94-97 % specific for UC, and combination ASCA+/pANCA-, 81-98% specific for CD (7).
- Thyroxine is elevated in thyroid nodules or Graves disease (causes diarrhea) and lowered in hypothyroidism (causes constipation)
- TSH (thyroid stimulating hormone) is elevated in adenoma of pituitary gland or in hypothyroidism
- Serotonin is elevated in carcinoid syndrome.
- Insulin is lowered in diabetes type 1 and may be elevated in diabetes type 2 or in insulinoma (a rare tumor of pancreas).
- Cortisol and aldosterone are lowered in Addison’s disease and congenital adrenal hyperplasia.
Heavy Metals and Drugs
Blood levels of lead, mercury, arsenic, lithium or iron (causing abdominal cramps) may be elevated in poisoning with these metals.
How to Prepare?
Do not eat overnight before the test.
The following tests may be done:
- Urine specific gravity is increased in dehydration.
- Urine 24h volume may be decreased (< 500 ml) in dehydration (due to diarrhea or vomiting) or increased (> 2.5 l) in diabetes or renal disease.
- Bilirubin may be increased in liver, gallbladder or biliary tract disease.
- Urine culture is usually positive in bacterial infection of urinary tract.
Autonomic neuropathy (that may cause diarrhea or constipation) may be diagnosed:
- by neurologist: physical examination, EMG, EKG, skin conduction tests (8);
- by gastroenterologist: gastric emptying test, etc.
- Lactoferrin test (sonoraquest.com)
- ESR and CRP levels in inflammatoty bowel disease (ncbi.nlm.nih.gov)
- Stool protein CD23 in food allergies (rxpgnews.com)
- Anti-gliadin IgA antibodies in the stool – evaluation (bmj.com)
- CHEM-20 blood testing (health.nytimes.com)
- Stool antibodies in ulcerative colitis and Crohn’s disease -evaluation (questdiagnostics.com)
- Autonomic neuropathy (emedicine.com)