Introduction: Who Should Undergo Diagnostics

Most people with diarrhoea don’t need to see a doctor or undergo any special tests. In fact, the majority of cases are mild and clear up on their own within one to two days without any medical intervention. However, there are certain situations where seeking professional advice becomes important, and diagnostic tests may be necessary to identify what’s causing your symptoms.^[1]

You should consider getting medical help if your diarrhoea lasts more than two days as an adult, or more than 24 hours in children. If you notice blood or mucus in your stool, this is another sign that something more serious may be happening and requires a doctor’s attention. A high fever — particularly one above 101 degrees Fahrenheit (or about 38 degrees Celsius) lasting more than 24 hours — alongside diarrhoea is also a reason to seek care.^[3]

Severe stomach pain or pain in the rectum shouldn’t be ignored either. These symptoms could indicate a more serious underlying condition. Dehydration is another major concern with diarrhoea, especially in young children, older adults, and people with weakened immune systems. Signs of dehydration include a dry mouth, feeling very thirsty, not urinating much, feeling dizzy, or having sunken eyes. If you or someone you’re caring for shows these signs, medical help is needed right away.^[2]

People who recently traveled to developing countries or areas with poor sanitation should also see a doctor if they develop diarrhoea. This type of illness, often called traveler’s diarrhoea, may be caused by bacteria or parasites that require specific treatment. Similarly, if you’ve recently been in hospital or taking antibiotics and then develop diarrhoea, it’s worth getting checked, as this could be a sign of a particular type of infection.^[3]

Certain groups of people are at higher risk of complications from diarrhoea and should keep in close contact with their doctor. This includes people over 65 years old, pregnant women, those currently taking antibiotics, and anyone with a weakened immune system due to conditions like HIV or cancer treatment. These individuals may need earlier evaluation and monitoring even if their symptoms seem mild at first.^[2]

If your diarrhoea is accompanied by severe vomiting that prevents you from drinking liquids, this is also a situation that requires medical help. Being unable to keep fluids down while losing water through diarrhoea creates a dangerous situation where dehydration can happen very quickly.^[10]

Diagnostic Methods

When you visit a healthcare professional about diarrhoea, they will usually start with a thorough conversation about your symptoms and medical history. This conversation is often the most important part of the diagnostic process. Your doctor will want to know how long you’ve had diarrhoea, what your stool looks like, whether you’ve traveled recently, what medications you’re taking, and whether you have other symptoms like fever or pain.^[7]

The physical examination comes next. Your doctor will check for signs of dehydration by looking at your mouth and eyes, checking your skin, and measuring your heart rate and blood pressure. They may gently press on your abdomen to check for tenderness or swelling. These simple checks can reveal a lot about how severe your condition is and whether you need immediate treatment.^[10]

Blood Tests

Blood tests are helpful in understanding how diarrhoea is affecting your body. A complete blood count can show if you have an infection or inflammation. This test looks at different types of cells in your blood and can reveal patterns that point to specific problems. For example, elevated white blood cells might suggest an infection fighting in your body.^[10]

Blood tests can also measure your electrolytes, which are important minerals like sodium and potassium that your body needs to function properly. Diarrhoea causes you to lose these minerals along with water, and checking their levels helps doctors understand if you’re becoming dehydrated. Tests of kidney function are often included because severe dehydration can affect how well your kidneys work.^[10]

A measurement called C-reactive protein can indicate inflammation in your body. If this level is normal, it can help rule out serious inflammatory conditions of the bowel. This is particularly useful when doctors are trying to distinguish between different possible causes of chronic diarrhoea.^[7]

For people with chronic or long-lasting diarrhoea, blood tests might include checking for celiac disease. This involves measuring specific antibodies in your blood, particularly something called anti-tissue transglutaminase immunoglobulin A. Celiac disease is a condition where your body reacts badly to gluten, a protein found in wheat, and it can cause ongoing diarrhoea.^[7]

Stool Tests

Examining your stool — what most people call a poop sample — is one of the most direct ways to find out what’s causing diarrhoea. However, not everyone needs this test. Doctors typically order stool tests when you have certain warning signs like bloody stools, severe illness, high fever, or symptoms lasting more than a week.^[13]

A stool culture looks for harmful bacteria that might be causing your symptoms. The laboratory grows bacteria from your sample to see what types are present. This can identify infections from bacteria like Salmonella, Shigella, or Campylobacter, which are common causes of bacterial diarrhoea.^[10]

Tests can also look for parasites in your stool. Parasites are tiny organisms that can live in your intestines and cause ongoing diarrhoea. However, testing for parasites isn’t routinely done unless you have specific risk factors, such as diarrhoea lasting more than seven days, recent travel to areas where parasites are common, or exposure to untreated water from lakes or streams.^[7]

If you’ve recently been in hospital or taken antibiotics, your doctor might test your stool for a bacterium called Clostridioides difficile (often shortened to C. diff). This organism can grow out of control when antibiotics kill off the normal, helpful bacteria in your gut. The test looks for toxins that this bacterium produces. Importantly, this test should only be done on liquid or loose stools, not on formed stool, as finding the bacteria in solid stool doesn’t necessarily mean it’s causing your symptoms.^[7]

Stool tests can also measure substances that indicate inflammation. Fecal calprotectin is a protein that appears in stool when there’s inflammation in the intestines. High levels suggest that inflammatory bowel disease might be the cause, rather than a simple infection or functional problem like irritable bowel syndrome.^[7]

Breath Tests

A hydrogen breath test is a simple, non-invasive way to check if you have trouble digesting certain sugars. The most common use is for diagnosing lactose intolerance, which happens when your body can’t properly break down lactose, the sugar found in milk and dairy products. During the test, you drink a liquid containing lactose, and then your breath is measured at regular intervals. If your body isn’t digesting the lactose properly, bacteria in your intestines will ferment it, producing hydrogen that shows up in your breath.^[10]

This same type of test can be used to check for other sugar absorption problems or to diagnose bacterial overgrowth in the small intestine, conditions that can both cause chronic diarrhoea.

Endoscopic Procedures

When simpler tests don’t provide answers, or when doctors suspect certain conditions, they may recommend looking directly inside your digestive system using a camera. These procedures are called endoscopies, and there are different types depending on which part of your digestive system needs examination.

A colonoscopy allows doctors to see the entire large intestine (colon). A thin, flexible tube with a tiny camera at the end is gently inserted through your rectum. As it moves through your colon, the doctor can see the lining of your intestine on a screen. If they spot anything unusual, they can take small tissue samples, called biopsies, to examine under a microscope. This procedure is particularly useful for diagnosing inflammatory bowel disease, microscopic colitis, or checking for cancer.^[10]

A flexible sigmoidoscopy is similar but examines only the lower part of the colon. It’s a shorter procedure and may be sufficient if doctors suspect the problem is in that area.^[10]

An upper endoscopy, sometimes called an esophagogastroduodenoscopy or EGD, examines the upper part of your digestive system. The camera tube goes through your mouth to look at your esophagus (food pipe), stomach, and the first part of your small intestine. This can help diagnose conditions like celiac disease or other causes of malabsorption, where your body isn’t absorbing nutrients properly, leading to diarrhoea.^[10]

Imaging Studies

Sometimes imaging tests that create pictures of your internal organs can help identify the cause of diarrhoea. A CT scan (computed tomography) uses X-rays and computers to create detailed cross-sectional images of your abdomen. This can show inflammation, blockages, or other structural problems in your intestines that might be causing your symptoms.^[10]

An ultrasound uses sound waves to create images and doesn’t involve radiation. It can be helpful in examining certain abdominal organs and looking for problems that might cause diarrhoea, though it’s less commonly used for this purpose than other tests.

Diagnostics for Clinical Trial Qualification

The sources provided don’t contain specific information about diagnostic tests used as standard criteria for enrolling patients in clinical trials for diarrhoea. Clinical trial requirements vary depending on the specific study and what condition or treatment is being investigated.