Workup for Chronic Diarrhea in a 68-Year-Old Woman
Begin with first-line blood tests (CBC, CRP, celiac serology with anti-tissue transglutaminase IgA and total IgA, thyroid function, basic metabolic panel) and stool studies (fecal calprotectin, stool culture/ova and parasites including Giardia testing), followed by colonoscopy given her age and 3-month symptom duration which suggests organic disease. 1
Initial Assessment Priority
This 68-year-old woman has chronic diarrhea (>4 weeks duration) with a relatively short 3-month history, which is concerning. Diarrhea lasting <3 months is considered suggestive of organic disease rather than functional disorders 1. While she lacks classic alarm features (no blood, no pain), her age and recent symptom onset warrant thorough investigation to exclude malignancy and inflammatory conditions.
Step 1: First-Line Blood Tests
Order the following blood work immediately:
- Complete blood count - to detect anemia (sensitive for small bowel enteropathy, particularly celiac disease) 1
- ESR or CRP - elevated levels have high specificity for organic disease 1
- Albumin - low levels suggest organic pathology 1
- Anti-tissue transglutaminase IgA with total IgA - to screen for celiac disease 1, 2
- TSH - thyrotoxicosis is a common endocrine cause 1
- Basic metabolic panel - assess electrolytes and renal function 2
Step 2: Stool Studies
Obtain stool samples for:
- Fecal calprotectin - to exclude colonic inflammation, though this is most validated in patients under 40 with suspected IBS 1
- Stool culture and ova/parasites - specifically test for Giardia 3, 2
- C. difficile testing if recent antibiotic use 1, 3
- Fecal immunochemical test (FIT) - can help guide priority of investigations even without visible bleeding 1
Step 3: Colonoscopy with Biopsies
Given her age (68 years) and recent change in bowel habit, colonoscopy is essential to exclude:
- Colorectal cancer - altered bowel habit in this age group requires endoscopic evaluation 1
- Microscopic colitis - obtain biopsies from right and left colon (not rectum) as this is a common cause in elderly patients 1, 4
- Inflammatory bowel disease 1
Step 4: If Initial Workup is Normal
If symptoms persist despite normal first-line tests, proceed with:
Bile Acid Diarrhea Testing
- SeHCAT scan (if available) or serum 7α-hydroxy-4-cholesten-3-one - make a positive diagnosis rather than empirical treatment 1, 5
Small Bowel Evaluation
- MR enterography (preferred over CT or barium studies) - to assess small bowel abnormalities 1
- Video capsule endoscopy - alternative for small bowel visualization 1
Pancreatic Function
Carbohydrate Malabsorption
- Hydrogen breath testing for lactose intolerance, or trial dietary lactose elimination 1
Critical History Elements to Obtain
While examining, specifically ask about:
- Medications - up to 4% of chronic diarrhea is drug-induced (magnesium, ACE inhibitors, NSAIDs, DPP-4 inhibitors, antibiotics) 1
- Alcohol use - common cause through multiple mechanisms 1
- Previous abdominal surgery - particularly ileal resection causing bile acid diarrhea 1
- Diabetes - autonomic dysfunction can cause diarrhea 1
- Weight loss - unintentional weight loss is an alarm feature requiring urgent investigation 1
- Nocturnal diarrhea - suggests organic rather than functional disease 1
- Family history - neoplastic, inflammatory bowel disease, or celiac disease 1
Common Pitfalls to Avoid
Do not assume IBS-D or functional diarrhea in a 68-year-old with new-onset symptoms. While functional disorders are the most common cause of chronic diarrhea overall 2, the short 3-month duration and her age make structural/organic causes more likely 1.
Do not skip colonoscopy. Even without blood in stool, colorectal cancer can present with painless diarrhea and altered bowel habit in this age group 1.
Do not order small bowel barium studies - they have poor sensitivity and specificity 1.