10 Lab Tests for Patients with Chronic Diarrhea

Chronic diarrhea, which means loose stools lasting more than four weeks, can be uncomfortable and frustrating and sometimes indicate an underlying issue. 

It's not just an occasional upset stomach—this persistent condition can affect a person's quality of life, leading to dehydration, nutrient deficiencies, and fatigue. Identifying the root cause is critical to managing and addressing chronic diarrhea.

To help pinpoint what might be contributing to ongoing digestive troubles, healthcare practitioners may suggest various lab tests. These tests can give insight into different aspects of health, such as digestion, inflammation, infection, and overall nutrient status. 

Here are 10 common lab tests to help patients and practitioners better understand and address chronic diarrhea.

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1. Complete Blood Count (CBC)

A Complete Blood Count (CBC) is a standard blood test that provides an overview of a patient's overall health by measuring different parts of the blood. It evaluates:

• White Blood Cells (WBCs): These cells are essential components of the immune system that help combat infections.
• Red Blood Cells (RBCs): These cells carry oxygen throughout the body.
• Hemoglobin & Hematocrit: These measure the amount and concentration of oxygen-carrying proteins in the blood.
• Platelets: These are important for blood clotting.

Relevance to Chronic Diarrhea

For patients experiencing chronic diarrhea, a CBC is one of the first tests that can help uncover possible causes. Specifically, it can help:

• Identify infections: Elevated WBCs can indicate an infection or inflammation in the body, which might be contributing to diarrhea.
• Detect anemia: Chronic diarrhea can lead to nutrient malabsorption, which can cause anemia—a low level of red blood cells or hemoglobin. This can result in symptoms like fatigue and weakness.

• Assess inflammation: Specific changes in the CBC, like increased WBCs or platelets, may suggest inflammatory conditions of the intestines, such as inflammatory bowel disease (IBD).

Here are examples of this test:

• CBC w/ Diff - Access Med Labs
• CBC w/ Diff - Boston Heart Diagnostics
• CBC with Differential and Platelets - Access Labcorp Draw
• Complete Blood Count - Boston Heart Diagnostics

2. Comprehensive Metabolic Panel (CMP)

A Comprehensive Metabolic Panel (CMP) is a blood test that measures several chemicals in the blood to assess the body's metabolism and organ function. It includes tests for:

• Electrolytes (sodium, potassium, calcium, chloride): These minerals are essential for fluid balance, muscle function, and nerve signaling.
• Blood glucose levels: An indicator of blood sugar control and energy use.
• Kidney function markers (BUN, creatinine) show how well the kidneys filter waste from the blood.
• Liver enzymes (AST, ALT, ALP, bilirubin): These enzymes indicate liver health and function.
• Proteins (albumin, total protein): Indicators of nutritional status and overall health.

Implications for Electrolyte Imbalances and Kidney Function

For patients with chronic diarrhea, a CMP can be essential for evaluating potential complications, such as:

• Electrolyte imbalances: Chronic diarrhea often leads to the loss of essential electrolytes like sodium, potassium, and calcium. Imbalances in these minerals can cause symptoms like muscle cramps, weakness, dehydration, and even heart issues. The CMP helps monitor these levels and assess the need for replenishment.
• Kidney function: Ongoing diarrhea can result in dehydration, which puts extra stress on the kidneys. The CMP measures waste products in the blood (BUN and creatinine) to see how well the kidneys function. Elevated levels could indicate kidney stress or damage.

Here are examples of this test:

• Comprehensive Metabolic Panel - Boston Heart Diagnostics
• Comprehensive Metabolic Panel - Empire City Laboratories Inc.
• Comprehensive Metabolic Panel - Access Labcorp Draw

3. Celiac Disease Panel

A Celiac Disease Panel is a blood test that screens for celiac disease, an autoimmune disorder triggered by consuming gluten (a protein found in wheat, rye, and barley). The most common test is for tissue transglutaminase antibodies (tTG-IgA). 

A high level of tTG-IgA antibodies typically indicates the body's immune response to gluten. Other tests may include endomysial antibodies (EMA-IgA) and deamidated gliadin peptide antibodies (DGP-IgA and IgG) to provide a fuller picture.

Importance in Diagnosing Gluten Sensitivity

Chronic diarrhea is a common symptom of celiac disease. A celiac disease panel helps identify whether gluten sensitivity contributes to the issue. If the test results are positive, further steps like a biopsy of the small intestine may be recommended to confirm the diagnosis. 

Diagnosing and managing celiac disease by eliminating gluten can help alleviate symptoms, including diarrhea, and prevent potential complications like nutrient deficiencies and intestinal damage.

Here are examples of this test:

• Celiac & Gluten Sensitivity - Doctor's Data
• Celiac Panel - US BioTek
• Celiac Disease Profile - Alletess Medical Laboratory
• Celiac Profile - Genova Diagnostics

4. Stool Culture and Sensitivity

A stool culture and sensitivity test are done to identify infectious agents like bacteria, viruses, or parasites that could be causing chronic diarrhea. The stool sample is examined for pathogens such as:

• Bacteria like Salmonella, Shigella, or Campylobacter.
• Parasites like Giardia or Cryptosporidium.
• Viruses that might affect the gut. This test helps determine if an infection is the underlying cause of chronic diarrhea, especially if the patient has a history of travel, food poisoning, or exposure to contaminated water.

Guiding Appropriate Antibiotic Therapy

Sensitivity testing can determine which antibiotics will most effectively treat the infection if a specific pathogen is identified. This targeted approach helps ensure the proper medication is used, improving treatment outcomes and avoiding the overuse of antibiotics that may not be necessary or effective.

Here are examples of this test:

• GI-MAP + Zonulin - Diagnostic Solutions‍
• GI Effects® Comprehensive Profile - 3 day - Genova Diagnostics‍
• GI 360 - Doctor's Data

5. Fecal Calprotectin Test

The fecal calprotectin test measures the calprotectin level, a protein found in white blood cells released during intestinal inflammation. Elevated levels of fecal calprotectin can indicate inflammation in the digestive tract, suggesting conditions like inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis.

Differentiating Between Inflammatory Bowel Disease and Irritable Bowel Syndrome

One key use of the fecal calprotectin test is to help differentiate between inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). While both can cause chronic diarrhea, IBS does not usually cause inflammation, so calprotectin levels would remain low. 

Elevated calprotectin suggests IBD, guiding further testing and appropriate treatment. This helps avoid unnecessary invasive procedures and ensures a more accurate diagnosis for managing symptoms.

Here are examples of this test:

• Calprotectin - Diagnostic Solutions
• Calprotectin Stool - Doctor's Data

6. Lactose Intolerance Test

The lactose intolerance test evaluates how well the body can digest lactose, the sugar in dairy products. The most common method used is the hydrogen breath test. In this test, an individual consumes a beverage containing lactose, and then the levels of hydrogen in their breath are measured at intervals to determine lactose digestion capability.

An increase in hydrogen suggests that lactose is not being properly digested, indicating a deficiency in lactase, the enzyme required for breaking down lactose.

If the test shows lactose intolerance, eliminating or reducing lactose-containing foods (like milk, cheese, and yogurt) can help manage symptoms like diarrhea, bloating, and abdominal pain. 

For those who are lactose intolerant, switching to lactose-free products or taking lactase enzyme supplements with meals can significantly improve gastrointestinal symptoms.

Here are examples of this test:

• Lactose Intolerance Breath Test - Aerodiagnostics LLC
• Lactose Malabsorption Breath Test - Commonwealth Diagnostics International, Inc.

7. Vitamin B12 and Folate Levels

Vitamin B12 and folate are essential nutrients in red blood cell production, DNA synthesis, and nerve function. Chronic diarrhea can lead to malabsorption of these nutrients, mainly if caused by conditions like celiac disease or small intestinal bacterial overgrowth (SIBO).

Testing for B12 and folate levels can identify deficiencies, which might contribute to additional symptoms like anemia, fatigue, and neurological changes.

Deficiencies in B12 and folate can have severe effects on neurological health, leading to symptoms such as numbness, tingling in the hands and feet, memory problems, and mood changes. 

Correcting these deficiencies through diet or supplementation is crucial for resolving symptoms related to chronic diarrhea and supporting nerve function and overall well-being.

Here are examples of this test:

• Vitamin B12 - Boston Heart Diagnostics
• Vitamin B12 - Empire City Laboratories Inc.
• Vitamin B12 & Folate - Access Med Labs
• Folate - Empire City Laboratories Inc.
• Folate - Boston Heart Diagnostics

8. Inflammatory Markers (CRP and ESR)

C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are blood tests that measure inflammation levels in the body.

The liver produces CRP in response to inflammation and can quickly rise with infections or inflammatory conditions. ESR measures how quickly red blood cells settle to the bottom of a test tube. 

A higher rate suggests increased inflammation. These non-specific markers can be elevated in various conditions but provide a useful general indicator of systemic inflammation.

Correlation with Gastrointestinal Disorders

Elevated CRP or ESR levels in chronic diarrhea may indicate inflammatory bowel disease (IBD) or other conditions involving inflammation of the intestines.

High-sensitivity CRP (hs-CRP) is a more sensitive version of the standard CRP test and can detect even lower levels of inflammation. It is often used to assess cardiovascular risk but may also help identify low-grade inflammation in chronic gastrointestinal disorders. 

An elevated hs-CRP level can indicate a milder or early inflammatory process in the intestines that the standard CRP or ESR tests might not detect. This can help uncover subtle inflammatory conditions and fine-tune diagnosis and treatment plans.

Lower levels suggest that diarrhea is less likely to be caused by an inflammatory condition and may be related to functional issues like irritable bowel syndrome (IBS).

While these tests do not provide a specific diagnosis, they can guide healthcare practitioners toward further testing and management, such as additional imaging or endoscopic evaluation. 

Here are examples of this test:

• ESR - Empire City Laboratories Inc.
• Sedimentation Rate (ESR) - Access Med Labs
• C-Reactive Protein, Inflammation (CRP) - Access Med Labs
• High-Sensitivity C-Reactive Protein - Empire City Laboratories Inc.
• High Sensitivity C-Reactive Protein (hs-CRP) - ZRT Laboratory

9. Small Intestinal Bacterial Overgrowth (SIBO) Breath Test

The SIBO Breath Test assesses the presence of an overgrowth of bacteria in the small intestine. 

The small intestine normally has fewer bacteria than the colon, but an overgrowth can disrupt digestion and absorption, potentially leading to chronic diarrhea, bloating, and gas. 

The test involves drinking a sugar solution (usually glucose or lactulose) and then measuring the levels of hydrogen and methane in the breath over time. These gasses are produced when bacteria ferment the sugar, so elevated levels indicate bacterial overgrowth.

If SIBO is detected, treatment may involve antibiotics, herbal antimicrobials, or dietary changes like a low-FODMAP diet. This diet is focused on minimizing the intake of fermentable carbohydrates that can promote bacterial overgrowth in the small intestine.

Addressing SIBO can help improve symptoms of chronic diarrhea and prevent future gastrointestinal issues.

Here are examples of this test:

• SIBO Breath Test - Aerodiagnostics LLC
• SIBO/IMO Lactulose Breath Test - Commonwealth Diagnostics International, Inc.
• Array 22 - Cyrex Laboratories

10. Fecal Elastase Test

The fecal elastase test quantifies the level of elastase, an enzyme produced by the pancreas, in the stool. Elastase helps digest proteins, and its levels in the stool reflect how well the pancreas is functioning. 

Low fecal elastase levels can indicate pancreatic insufficiency, where the pancreas fails to produce adequate enzymes for proper food digestion.

Pancreatic insufficiency can be associated with conditions like chronic pancreatitis, cystic fibrosis, or pancreatic cancer. 

By identifying low elastase levels, healthcare practitioners can diagnose pancreatic insufficiency and recommend treatments like pancreatic enzyme replacement therapy (PERT) to improve digestion and nutrient absorption. 

This can significantly improve symptoms of diarrhea and nutrient deficiencies caused by malabsorption.

Elastase by Doctor's Data is an example of a single biomarker test. It is also included in these panels:

• Stool Chemistries - Doctor's Data
• Comprehensive Stool Analysis - Mosaic Diagnostics
• Comprehensive Stool Analysis + Parasitology - 3 Day - Doctor's Data

Additional Considerations

While lab tests like blood work, stool analysis, and breath tests can provide valuable clues to the cause of chronic diarrhea, sometimes further investigation is needed. Advanced tests may be necessary in the following situations:

• Persistent or severe symptoms: If symptoms are not improving with initial treatments or are particularly severe (e.g., significant weight loss, blood in stools), a more detailed evaluation is warranted.
• Abnormal lab results: When initial lab tests indicate possible inflammation, infection, or malabsorption, advanced tests like a colonoscopy can be used to visually examine the colon and obtain tissue biopsies. Upper endoscopy may also be performed if small intestine involvement is suspected.
• Imaging studies: Abdominal ultrasound, CT scan, or MRI might be ordered to detect structural abnormalities, blockages, or other issues within the intestines or surrounding organs contributing to diarrhea.
• Suspected inflammatory or autoimmune conditions: When lab tests show signs of inflammation or suggest autoimmune involvement (e.g., celiac disease panel), additional endoscopic procedures or imaging studies can help confirm the diagnosis and assess the extent of intestinal damage.

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Key Takeaways

• Chronic diarrhea requires lab tests like CBC, CMP, and stool analysis to help find the underlying cause.
• Testing for Vitamin B12, folate, CRP, and ESR levels can help identify nutrient deficiencies or inflammation.
• Celiac disease panels and lactose intolerance tests help find sensitivities to gluten or lactose that might cause symptoms.
• A SIBO breath test can reveal bacterial overgrowth in the small intestine, which may be contributing to diarrhea.
• The fecal elastase test assesses pancreatic function to ensure proper digestion and absorption.
• In complex cases, advanced tests like colonoscopy or imaging may be necessary.
• Lab results should be interpreted alongside a patient's symptoms and history for accurate diagnosis and treatment.