What is the Difference Between Osmotic and Secretory Diarrhea?

Osmotic and secretory diarrhea are two types of chronic watery diarrhea with distinct differences:

1. Osmotic diarrhea occurs when unabsorbed substances draw water from the plasma into the intestinal lumen along osmotic gradients. Common causes of osmotic diarrhea include:

• Consuming substances that cannot be absorbed, such as lactose, artificial sweeteners, or certain carbohydrates found in fruit juices.
• Side effects of medications.

1. Secretory diarrhea results from disordered electrolyte transport and is more commonly caused by decreased absorption rather than net secretion. Common causes of secretory diarrhea include:

• Bacterial infections, such as salmonella and E. coli.
• Parasitic infections, such as cryptosporidium and Giardia.
• Viral infections, such as norovirus and viral hepatitis.
• Digestive disorders, such as celiac disease and ulcerative colitis.
• Genetic disorders, such as congenital chloride diarrhea.

Two ways to distinguish between osmotic and secretory diarrhea are:

• Response to fasting: Stool volume decreases with fasting in osmotic diarrhea, while secretory diarrhea typically continues unabated with fasting.
• Fecal osmotic gap: This is calculated by adding the stool sodium and potassium concentration, multiplying by 2, and subtracting this amount from 290 mmol/L. A fecal osmotic gap greater than 50 mmol/L suggests an osmotic cause for diarrhea, whereas a gap less than 50 mmol/L supports a secretory origin.

Comparative Table: Osmotic vs Secretory Diarrhea

Osmotic and secretory diarrhea are two different types of watery diarrhea characterized by loose bowel movements and dehydration. Here is a table highlighting the differences between the two:

Both types of diarrhea can cause electrolyte abnormalities and be diagnosed through physical examination and blood tests.