Factitious Diarrhea Diagnosis and Management

Key Diagnostic Features

A measured stool osmolality of 200 mosmol/L, which is significantly below the normal plasma osmolality of 290 mosmol/kg, indicates that water or a hypotonic solution has been added to the stool specimen, suggesting dilutional factitious diarrhea 1, 2, 3
When faecal osmolality is less than 290 mosmol/kg, the specimen has been diluted with water or hypotonic fluid, indicating dilutional factitious diarrhea 1, 2, 3

Factitious diarrhea represents 20% of cases at tertiary referral centers, making it the most common cause of diarrhea of previously undetermined origin 4, 1, 2
In patients who have undergone extensive evaluation, 33% were found to be taking laxatives or diuretics 4, 1, 2
Normal vital signs and physical examination despite reported severe symptoms, such as 8-10 bowel movements daily and significant weight loss, are consistent with factitious diarrhea 4
Normal serum laboratory studies despite purported significant volume losses are also consistent with factitious diarrhea 4
High stool output with otherwise unremarkable findings is another characteristic of factitious diarrhea 3

The American Gastroenterological Association recommends performing supervised inpatient stool collection with concurrent laxative screening to confirm the diagnosis of factitious diarrhea 4, 1
Collecting stool specimens under direct observation to prevent specimen tampering is a crucial step in diagnosing factitious diarrhea 4, 3
Screening urine for anthraquinones, bisacodyl, and phenolphthalein, and screening stool for magnesium and phosphate, can help identify the cause of factitious diarrhea 4, 3, 1
Using spectrophotometric or chromatographic analysis rather than alkalinization assays is recommended for detecting laxatives in stool specimens 4
Repeated testing may be necessary, as patients with factitious diarrhea may ingest laxatives intermittently 1, 2

The American College of Gastroenterology advises against relying on osmotic gap calculations when measured stool osmolality is abnormally low, as the primary abnormality is specimen dilution, not the gap itself 1, 2
Patients with factitious diarrhea often have few physical cues despite potentially severe reported symptoms, and may have a psychiatric history or connections with health professions 4, 1
Hospital admission may be required to document true stool volumes while preventing specimen tampering in patients with suspected factitious diarrhea 4, 3