Diarrhea and Laboratory Tests

Diarrhea is indicative of a gastrointestinal ailment. It entails passing loose stool frequently that may be accompanied by cramping, stomach pain (especially in the abdomen), vomiting, nausea, and fatigue. In some cases, the stool may also contain mucus and or blood.

Acute Diarrhea lasts between one and a few days. Most adults tend to experience Diarrhea several times every year without complications. Such bouts of acute Diarrhea tend to clear themselves without needing any medical treatment. However, when a diarrhea bout lasts anywhere between two and four weeks, it is considered chronic. Chronic diarrhea cases can be persistent or intermittent over the period.

Chronic and severe Diarrhea tends to be very dangerous, especially among the elderly and young children. Severe and or persistent diarrhea bouts can cause electrolyte imbalance and dehydration. Among infants, Diarrhea can cause severe dehydration in as little as one or two days. Electrolyte imbalance can be life-threatening, whether there is too much or too little of electrolytes in the body. As such, some severe diarrhea cases necessitate hospitalization.

Common Causes Of Diarrhea

Numerous infectious and non-infectious causes cause acute and chronic diarrhea bouts.

Common Infectious Causes:

Bacterial, viral, and parasitic infections are known to cause Diarrhea that can last from a few days to weeks. In some cases of individuals with a suppressed immune system such (for instance, among patients with cancer, AIDs, or organ transplants), Diarrhea might linger, resulting in chronic Diarrhea. These causes of Diarrhea are infectious. The bacteria, virus, or parasite is shed into a person’s stool and then passed to other people via oral contact with any of the contaminated surfaces. The most common contamination method is consuming contaminated foods and water.

Once you get infected, you will pass on the infection to others around you, unless you follow high standards of sanitation, especially washing your hands. This tends to be a challenge for environments with young children (such as daycare centers) and in nursing homes. It does not take a lot to cause a bacterial or parasitic infection outbreak. It can arise from infected foods at a restaurant, picnic, or any other eatery outlet. In other cases, drinking contaminated water can result in an outbreak.

When traveling to other countries, especially emerging nations, you may be exposed to several disease-causing bacteria, viruses, and parasites. Something as simple as unwashed fruit, ice cubes, or food from vendors can expose to illness.


In the United States, Norovirus is the leading cause of acute gastroenteritis, the severe and or sudden illness of the digestive tract. Also called Norwalk-like virus, the Center for Disease Control and Prevention (CDC) says this virus is the leading cause of waterborne and food illnesses. The virus is very contagious, spreading from one person to another and can contaminate water and foods. There are many recorded cases of the norovirus outbreaks in cruise ships, schools, nursing homes, military bases, and other places with high human population concentration.

Rotavirus, on the other hand, is renowned for causing severe Diarrhea among young kids. Typically, the virus spread through contact with infected stool. To prevent the spread of this virus, you must wash your hands after every diaper change. Regularly clean the surface of all objects your kids come in contact with, including the changing table, toys, and much more. You can also give your infants an oral vaccine that has over 98% effectiveness in rotavirus infection prevention.

Other viruses that cause Diarrhea include Cytomegalovirus (CMV), Hepatitis A, and Adenoviruses.

Bacteria: Bacteria cause Diarrhea by producing toxins or infection.

In the case of infections, you ingest live bacteria. Once on the intestinal tract, they, later on, grow and multiply, causing Diarrhea. The most common types of bacteria responsible for Diarrhea include:

  • Salmonella, which is commonly found in raw poultry, raw eggs, and in pet reptiles. A salmonella infection will produce symptoms between 12 and 72 hours of ingesting the bacteria, and it can last between 4 and 7 days. Typically, a salmonella infection resolves without needing any treatment. However, among young children and the elderly, Diarrhea may become too severe, requiring hospitalization and antibiotic treatments. Salmonella serotype Typhimurium Enteritidis and Salmonella serotype in the U.S., especially among travelers.
  • Campylobacter. Commonly found in unpasteurized milk, cheese, under-cooked poultry, and in contaminated water. Campylobacter causes water and or bloody stools with symptoms arising 2 to 5 days after the infection. The illness lasts about one week. Supportive care is enough to overcome the disease, but in some cases, especially prolong illness cases, antibiotics treatment is necessary.
  • Yersinia species. These bacteria are commonly found in seafood, unpasteurized milk, and under-cooked pork. A Yersinia infection is associated with ‘chitlins,’ a delicacy cooked from hogs’ intestines and often prepared during holidays. As such, there tends to be an increase in the number of Yersinia infection cases during winter. Yersinia enterocolitica is the most common Yersinia species.
  • Vibrio species. It is typically found in raw oysters and contaminated seafood. Vibrio Cholerae is the bacteria that causes cholera. However, Vibrio parahaemolyticus is the most prevalent.

Some bacteria produce diarrhea-causing toxins. The most common of such bacteria include:

  • Staphylococcus aureus. This is a common bacterium typically found on the hair and skin, as well as the throats and noses of many people. It is responsible for many cases of food poisoning. The bacteria may contaminate food during preparation, and if the food is improperly cooked and or not refrigerated, there is a chance of getting food poisoning. The bacteria produce toxins that cause severe symptoms of vomiting, nausea, and Diarrhea in just a few hours after consuming the contaminated food.
  • Bacillus cereus. Bacillus cereus is found in many different foods, especially rice. It is also prevalent in leftover foods that have stayed at room temperature for long. Symptoms of poisoning include Diarrhea and cramps come about between 6 and 15 after consuming contaminated foods.
  • Clostridium difficile (C diff) diarrhea caused by Clostridium difficile’s toxins is indicative of antibiotic-related issues. Antibiotic treatment can destroy your gut flora by killing the good bacteria in the gastrointestinal tract. The good bacteria are beneficial to your overall health as they help digest food and protect against harmful bacteria. When you destroy the good bacteria, you make it easier for harmful bacteria such as C. difficile to grow, thrive, and multiply, which in turn causes Diarrhea.
  • Clostridium perfringens. This strain of bacteria is commonly found in poultry and raw meat. Ingesting poorly cooked and or poorly stored meat can cause a Clostridium perfringens infection. The bacteria have developed a mechanism to overcome harsh conditions such as high temperatures. For instance, it forms spores that resist high temperatures. After the cooked food cools down, the bacteria sprout again and begins to grow. When you ingest the bacteria, you get an acute infection characterized by Diarrhea and cramping (without vomiting and fever) within 8 to 12 hours. The symptoms last less than 24 hours.
  • Clostridium botulinum. These bacteria are responsible for botulism, a disease caused by improper handling of food during the canning process. The bacteria produce a toxin that results in Diarrhea, vomiting, muscle weakness, drooping eyelids, blurred and or double vision, dry mouth, difficulty swallowing, and slurred speech. When left untreated, the disease causes muscle paralysis, affecting the breathing system, arms, legs, and trunk. To prevent cases of foodborne botulism, you should follow the best practices in home-canning. Exposing the bacteria to high temperature is the best way to kill them.
  • Shigella. These bacteria stem from water and food contaminated with stool. Some of the Shigella species produce toxins that cause reactive arthritis, as well as a hemolytic uremic syndrome (HUS), an ailment associated with kidney failure, and the destruction of red blood cells. Additionally, some species, such as Shigella dysenteriae, cause fever, severe bloody Diarrhea, and dysentery.
  • Escherichia coli 0157:H7 (E. coli). Most humans and animals have E. coli in their digestive tract. However, the vast majority of E. coli strains do not cause harm. However, the STEC (Shiga toxin-producing E. coli) produce toxins in the form of Shiga toxin, which in turn leads to bloody Diarrhea. Serious E. coli infections are known to spread from undercooked meat such as hamburger. It also spread from person to person. Young children and the elderly some out worse when infected with E. coli owing to the severe nature of STEC-caused infections.

Parasites: Typical parasites that cause Diarrhea in the U.S. are:

  • Giardia species
  • Entamoeba histolytica
  • Cryptosporidium parvum

These parasites are commonly found in lakes and mountain streams. Additionally, they may also inhabit hot tubs, swimming pools. On rare occasions, they may find their way into water supplies.

Other parasites, including tapeworms and roundworms, can also cause infections.

In the warm parts of the world, especially in developing countries, pathogenic bacteria tend to be of greater range, and they frequently cause disease outbreaks. These include roundworms, hookworms, flatworms, and flukes. People get infected by ingesting food and drinks contaminated with ova (the parasite’s eggs). Some parasites are also capable of penetrating the skin.

The Non-Infectious Causes Of Diarrhea

Non-infectious causes typically cause chronic Diarrhea, Diarrhea that alternates with constipation, and sporadic Diarrhea.

Among these causes include:

  • Inflammatory bowel diseases, such as ulcerative colitis and Crohn’s disease
  • Bowel dysfunction, for instance, caused by irritable bowel syndrome
  • Colon polyps or cancer
  • Chemotherapy or gastrointestinal or abdominal radiation
  • Food sensitivities or intolerances, including celiac disease and lactose intolerance
  • Use of laxatives
  • Pancreatic diseases
  • Malabsorption disorders such as cystic fibrosis
  • Gallbladder or stomach surgery (the rate of food passage through the digestive system may change)
  • Endocrine diseases, including thyroid and diabetes disease
  • Carcinoid syndrome (a group of symptoms that include Diarrhea found among people with carcinoid tumors found in the colon, small intestine, or appendix)
  • Medication that causes Diarrhea as a side effect


As the first step of treatment, the healthcare provider should learn about your Diarrhea. Keep in mind that the quantity, frequency, and consistency of normal bowel movements are unique to every individual. Factors such as the food eaten, a person’s metabolisms and level of physical engagement, stress levels, medication one is taking, and the total amount of fluids taken influence the bowel movement. The healthcare practitioner will be interested in out-of-ordinary things and alterations associated with Diarrhea. To this end, they will ask a series of questions to determine the lab tests to run. The questions include:

  • Is there mucus or blood in the stool?
  • How frequently do you pass stool?
  • When did the Diarrhea start?
  • Do you have any other symptoms, including abdominal pain, fatigue, fever, nausea, or headache?
  • Have you taken antibiotics lately?
  • Have you been camping recently? Have you traveled out of the country? Where?
  • What is the color, consistency, and volume of the diarrhea stools?
  • Where and what have you eaten recently?
  • Are any of your close acquaintances, family members, or co-workers ill?

In cases where the patient’s Diarrhea is uncomplicated and clears after a few days, the doctor may not need to know what caused the gastrointestinal (G.I.) upset. However, in cases of severe, bloody, or long-lasting Diarrhea, the doctor may order several tests. The same case applies to patients who have traveled outside the U.S., and there is a possibility that some close them may be infected.

Laboratory Tests For Infectious Causes of Diarrhea

  • A Panel Tests For Detecting Gastrointestinal Pathogens         

Sample – Stool  

Description – This is a molecular test done to detect bacteria, viruses, and parasites; the panel of tests done determines the variety of pathogens identified.

Sample – Stool

Description – Stool samples are cultured in special nutrients media that allow pathogens to grow and thrive while inhibiting normal flora (bacteria found in the digestive tract) from growing. This test allows for the detection of several different bacteria. However, labs usually evaluate stool cultures with a focus on identifying common intentional pathogens such as:

  • Campylobacter species
  • Shigella species
  • Salmonella species

Sample – Stool  

Description – Done to detects the presence of toxin produced by C. difficile

Sample – Stool  

Description – #1. Toxin test – detects the Shiga toxin directly (used in conjunction with stool cultures)

#2. Pulsed-field Gel Electrophoresis (PFGE) is used in public health laboratories to detect and identify suspected E. coli subtypes in the event of an outbreak.

#3. Genetic tests – the rapid molecular tests (PCR) is used to identify Shiga toxin 1 gene (stx1) as well as Shiga toxin 2 gene (stx2)

  • Stool WBC            

Sample – Stool  

Description – This test is done to detects the presence of white blood cells in the stool owing to a bacterial infection, like Clostridium difficile

Antigen Test For Detecting Rotavirus         

Sample – Stool  

Description – A rapid antigen test done to detect the cause of Diarrhea common in children

  • Ova And Parasite Exam    

Sample – Stool  

Description – An evaluation of the stool using a microscope to detect parasites and their ova (eggs and or cysts).

  • Antigen Tests To Detect Specific Parasites:
  • Entamoeba histolytica
  • Giardia lamblia
  • Cryptosporidium parvum

Sample – Stool

Description – This is a test to detect the protein structure of the parasites. It is more sensitive than the O&P microscope exam, and a specific test is done to identify the parasites mentioned above

  • Antibody Tests For G.I. Parasites  

Sample – Blood 

Description – Some reference labs offer these tests. The tests are useful in detecting current infections but can also check for chronic or past diseases.

Examples of Tests for Non-infectious Causes of Diarrhea

  • Trypsin/Chymotrypsin      

Sample – Stool  

Description – Trypsin/chymotrypsin are two enzymes found in the stool when one’s pancreas is functioning well. The test helps determine whether the pancreas is functioning well. When there are low levels of the enzymes, it might indicate pancreatic disease or cystic fibrosis (C.F.).

  • Stool WBC            

Sample – Stool  

Description – An increased count of white blood cells in the stool might be indicative of inflammatory bowel disease (IBD).

  • Fecal Fat 

Sample – Stool  

Description – The test is done to measure the fat level/content in the stool. When there is an increased level of fat, it indicates malabsorption that can be caused by pancreatic insufficiency, celiac disease, or even cystic fibrosis.

Sample – Not applicable

Description – This test involves the oral food challenge, which helps diagnose food allergies. The tests are laborious, time-consuming, and require close supervision of the examiner owing to the potential of severe reactions such as life-threatening anaphylaxis. An alternative analysis is the food elimination test, which involves eliminating the suspected foods from the diet, and later on, reintroducing them one by one to determine which ones cause problems.

Sample – Sample – Blood             

Description – the Tissue transglutaminase antibody (tTG), IgA class primarily screens for celiac disease. The test is specific and exceptionally sensitive in testing for celiac disease. Other tests the medical practitioner may order include the total IgA and deamidated gliadin peptide antibodies (anti-DGP), IgG class of tTG, IgG, or IgA.

  • Lactose Tolerance Testing

Sample – Breath, blood 

Description – The test measures the amount of hydrogen in the patient’s breath or the chances in the glucose level in the patient’s blood after ingesting a standard amount of lactose to determine whether or not the patient can digest lactose properly.

  • Xylose Absorption Test      

Sample – Blood, urine    

Description – This test is done to determine how well the patient absorbs xylose. The patient ingests a standard amount of xylose, and then the levels of xylose are measure in the blood and urine. This helps determine whether they can absorb carbohydrates properly.

Sample – Stool  

Description – Detect inflammation resulting from IBD.

Sample – Blood 

Description – This test looks for anti-Saccharomyces cerevisiae antibodies (ASCA), an immune protein present in a patient with IBD.

Sample – Stool  

Description – These are tests done to detects any digestive tract bleeding emanating from colon cancer.

Sample – Blood 

Description – These are tests done to detect and diagnose carcinoid tumors, which, while rare, can cause chronic Diarrhea.

In some cases, a biopsy of the small intestines is ordered to detect parasitic infections, tumors, or celiac disease.

Other tests are performed to help determine the general health of an individual, which in turn helps unearth clues of diarrhea causes. Such tests include:

  • Complete Blood Count (CBC) – Helps detect anemia, which in turn detects an infection. For instance, in instances of elevated white blood cells eosinophil, it indicates a possibility of parasitic infection.
  • Osmolality – Urine, blood, or stool sample can be examined to evaluate electrolyte balance.