What tests to order for a patient presenting with nausea, vomiting, and diarrhea?

From the Guidelines

For patients presenting with nausea, vomiting, and diarrhea, I recommend starting with stool testing for Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and STEC, as well as considering tests for norovirus, rotavirus, or other viral pathogens, especially during outbreaks or in pediatric patients, as suggested by the 2017 Infectious Diseases Society of America clinical practice guidelines 1. When evaluating these patients, it's crucial to consider their clinical presentation, including the presence of fever, bloody or mucoid stools, severe abdominal cramping or tenderness, or signs of sepsis.

• Stool culture and sensitivity testing should be performed to identify bacterial pathogens and guide antibiotic therapy, if necessary.
• Testing for C. difficile should be considered, especially in patients with recent antibiotic use or healthcare exposure, as recommended by the 2017 guidelines 1.
• For patients with chronic diarrhea, testing for Giardia is recommended, using either a Giardia antigen test or polymerase chain reaction, as suggested by the 2019 AGA clinical practice guidelines 1.
• Additional tests, such as abdominal imaging or endoscopy, may be necessary if symptoms are severe or persistent, or if there is suspicion of an underlying inflammatory or obstructive condition.
• Blood tests, including complete blood count, comprehensive metabolic panel, and electrolytes, should be performed to assess for dehydration, infection, or organ dysfunction.
• In patients with relevant travel history, specific tests for tropical infections like Entamoeba histolytica may be warranted, as recommended by the 2017 guidelines 1.
• Blood tests for inflammatory markers, such as CRP or ESR, can help identify inflammatory bowel disease if symptoms are chronic. These tests help determine whether the cause is infectious, inflammatory, medication-related, or due to other systemic conditions, guiding appropriate treatment and preventing complications from dehydration and electrolyte imbalances.

From the FDA Drug Label

The most common adverse reactions in adults for the: prevention of chemotherapy-induced (greater than or equal to 5%) are: headache, malaise/fatigue, constipation, diarrhea. The most common adverse reactions in adults for the: prevention of radiation-induced nausea and vomiting (greater than or equal to 2%) are: headache, constipation, and diarrhea. The most common adverse reactions in adults for the: prevention of postoperative nausea and vomiting (greater than or equal to 9%) are: headache and hypoxia.

Tests to Order:

• Electrolyte panel to assess for electrolyte abnormalities, particularly in patients with diarrhea or vomiting.
• Electrocardiogram (ECG) to monitor for QT interval prolongation, especially in patients with congenital long QT syndrome or those taking other QT-prolonging drugs.
• Complete blood count (CBC) to evaluate for signs of infection or inflammation.
• Liver function tests (LFTs) to monitor for hepatic impairment, as ondansetron is contraindicated in patients with severe hepatic impairment.
• Consider imaging studies (e.g., abdominal X-ray or CT scan) if there is suspicion of gastrointestinal obstruction or ileus, particularly in patients with risk factors for these conditions 2.

From the Research

Diagnostic Approach

To determine the underlying cause of nausea, vomiting, and diarrhea, a thorough diagnostic approach is necessary. The following steps can be taken:

• Define the patient's symptoms and determine if they are acute or chronic 3, 4
• Consider medication or toxin adverse effects, as well as other potential causes such as gastrointestinal diseases, metabolic and endocrine conditions, and psychogenic disorders 3, 4
• Use the patient's presentation, severity of symptoms, and physical examination findings to formulate a differential diagnosis and guide evaluation 3, 4

Laboratory Tests

The following laboratory tests may be ordered to evaluate nausea, vomiting, and diarrhea:

• Urinalysis, urine pregnancy testing, complete blood count, comprehensive metabolic panel, amylase and lipase levels, thyroid-stimulating hormone level, and stool studies with cultures 5
• C-reactive protein, anti-tissue transglutaminase immunoglobulin A (IgA), total IgA, and a basic metabolic panel to evaluate for pathologies such as celiac disease or inflammatory bowel disease 6

Imaging Studies

The following imaging studies may be ordered to evaluate nausea, vomiting, and diarrhea:

• Abdominal radiography, ultrasonography, and computed tomography to evaluate for gastrointestinal causes 5
• Computed tomography of the head if an acute intracranial process is suspected 5
• Esophagogastroduodenoscopy if gastroparesis or gastric malignancies are suspected 5, 7
• Gastric emptying study if gastroparesis is suspected 5, 7

Specialized Tests

The following specialized tests may be ordered to evaluate nausea, vomiting, and diarrhea:

• Stool studies to categorize diarrhea as watery, fatty, or inflammatory 6
• Tests for bile acid malabsorption, microscopic colitis, endocrine disorders, and some postsurgical states if secretory diarrhea is suspected 6
• Tests for carbohydrate malabsorption syndromes and laxative abuse if osmotic diarrhea is suspected 6
• Tests for malabsorption or maldigestion, including disorders such as celiac disease, giardiasis, and pancreatic exocrine insufficiency if fatty diarrhea is suspected 6