Approach to diarrhea (chronic): Clinical sciences

Chronic diarrhea is defined as more than three loose stools per day for at least four weeks. Now, based on the underlying cause, chronic diarrhea can be divided into several types, including steatorrhea, secretory, osmotic, inflammatory, dysmotile, and iatrogenic diarrhea.

Now, if your patient presents with chronic diarrhea, first, obtain a focused history and physical examination. Your patient will typically report having more than 3 loose stools per day, or a significant change in stooling habits for at least 4 weeks. In some cases, your patient might report abdominal pain. Physical examination may reveal abdominal tenderness and hyperactive bowel sounds.

With these findings, you should suspect chronic diarrhea, so your next step is to assess the type of chronic diarrhea. To do so, order labs, which could include CBC with differential, CMP, vitamins including A, D, B12, and K, along with iron and calcium levels. You could also order inflammatory markers, such as ESR and CRP, as well as TSH and a tissue transglutaminase IgA test. Lastly, other helpful stool studies include stool electrolytes, fecal fat content, occult blood, and tests for fecal calprotectin or lactoferrin.

Now, here’s a clinical pearl! Keep in mind that the labs you choose to order in a particular situation will depend on the history and physical examination. For example, if your assessment findings suggest inflammatory diarrhea, you’ll need to order fecal calprotectin or lactoferrin. These are proteins found in neutrophils, which are released during cell lysis, and their detection in stool samples indicates an inflammatory process in the gastrointestinal tract.

First, let’s focus on individuals with steatorrhea! In this case, your patient will often describe their stool as greasy, foul-smelling, and difficult to flush. They might also report increased flatus and weight loss. Labs typically reveal low levels of albumin, vitamins A, D, B12, and K, along with low iron and calcium; while the stool studies will show an elevated fecal fat content. These findings are highly suggestive of steatorrhea, so your next step is to assess the underlying cause!

If your patient has a family history of autoimmune disease, and their labs reveal positive tissue transglutaminase IgA antibodies, consider celiac sprue. In this case, order an upper gastrointestinal endoscopy with small intestinal biopsies. If the biopsies reveal villous atrophy, crypt hyperplasia and an increased number of intraepithelial lymphocytes, diagnose celiac sprue, otherwise known as celiac disease.

However, if your patient also has a history of alcohol use disorder, chronic pancreatitis, or other disorders affecting the pancreas like cystic fibrosis, consider pancreatic insufficiency! In this case, check the patient’s amylase and lipase levels and order a fecal pancreatic elastase-1 test. The fecal pancreatic elastase-1 test measures the levels of a pancreatic enzyme called chymotrypsin-like elastase in the stool. Because it doesn’t degrade as it makes its way through the intestine, it’s a reliable marker of pancreatic function. Additionally, consider ordering a CT scan of the abdomen.

If the amylase and lipase levels are normal, the fecal pancreatic elastase-1 is 200 micrograms per gram or less, and the CT scan reveals pancreatic calcifications, you can diagnose pancreatic insufficiency as a cause of steatorrhea.

Next, let’s take a look at individuals that are reporting watery stools! In this case, consider secretory or osmotic diarrhea. Your next step is to calculate the stool osmotic gap.

Here’s a clinical pearl to keep in mind! Stool osmolarity is normally the same as plasma osmolarity, around 290 milliosmoles per kilogram, and is primarily determined by sodium, potassium, and water concentrations in the stool. To calculate the stool osmotic gap, add the stool sodium level to the stool potassium level, multiply the sum by two, then subtract the product from 290. A normal stool osmotic gap is usually less than 50 milliosmoles per kilogram.

Now, if the stool osmotic gap is less than 50 milliosmoles per kilogram, and your patient reports stool volume that’s greater than 200 milliliters per day that does not change with fasting, diagnose secretory diarrhea.

Secretory diarrhea typically occurs due to either malabsorption or intestinal hypersecretion of ions, such as sodium, potassium, chloride, and bicarbonate. This causes water to move across the intestinal lining into the lumen, resulting in a normal stool osmolar gap!

Next, assess the underlying cause of secretory diarrhea. If your patient has a history of Crohn ileitis or a terminal ileum resection, consider bile acid diarrhea, which results from excessive bile acids in the gastrointestinal lumen. To confirm the diagnosis, order a fecal bile acid level or start an empiric trial of bile acid sequestrant medication.

If the bile acid excretion level is elevated, or there’s improvement in stooling when taking bile acid sequestrants, diagnose bile acid diarrhea.

However, if secretory diarrhea is associated with a report of episodic cutaneous flushing and venous telangiectasias on physical exam, consider carcinoid syndrome, and order a 24-hour urine collection for 5-hydroxyindoleacetic acid, or 5-HIAA, which is the end product of serotonin metabolism. High levels of 5-HIAA suggest carcinoid syndrome.