How should I evaluate an elderly patient (≥65 years) with a one‑month history of chronic diarrhea (3–4 stools per day), abdominal pain relieved by defecation, and impaired renal function (estimated glomerular filtration rate 38 mL/min/1.73 m²)?

Workup for Elderly Patient with Chronic Diarrhea and Impaired Renal Function

This elderly patient requires colonoscopy with biopsies as the priority investigation, followed by coeliac serology, faecal calprotectin, and consideration of bile acid diarrhoea testing, with careful attention to contrast-enhanced CT only if absolutely necessary given the GFR of 38 mL/min/1.73 m². 1

Initial Non-Invasive Testing (Can Be Done in Primary Care)

• Coeliac serology (anti-tissue transglutaminase IgA with total IgA) should be obtained immediately, as coeliac disease can present atypically in the elderly and is a treatable cause of chronic diarrhea 1, 2

• Faecal calprotectin to screen for inflammatory bowel disease and microscopic colitis, which are common in elderly patients and often missed 1

• Complete blood count and C-reactive protein to assess for anemia, inflammation, and systemic disease 2

• Basic metabolic panel (already done, showing GFR 38) to evaluate electrolyte abnormalities from chronic diarrhea 2

• Thyroid function tests as hyperthyroidism can cause chronic diarrhea and is more common in elderly patients 3, 4

Colonoscopy with Biopsies: The Critical Investigation

All elderly patients with chronic diarrhea should undergo colonoscopy with biopsies of both right and left colon, regardless of macroscopic appearance. 1 This is non-negotiable because:

• Colorectal cancer risk increases significantly with age, and a low threshold for colonoscopy is justified given the frequency and clinical significance of colonic neoplasia in older subjects 1

• Microscopic colitis (lymphocytic and collagenous colitis) is a common cause of chronic watery diarrhea in elderly patients but appears endoscopically normal—diagnosis requires histological examination 1, 3

• The symptom pattern (abdominal pain relieved by defecation, 3-4 stools daily for one month) does not reliably exclude inflammatory bowel disease, microscopic colitis, or bile acid diarrhoea despite meeting Rome IV criteria for IBS 1

• Biopsies should be obtained even if the mucosa appears normal, as microscopic colitis and other conditions require histological diagnosis 1

Special Considerations for Impaired Renal Function (GFR 38)

The GFR of 38 mL/min/1.73 m² represents Stage 3b chronic kidney disease and requires specific medication adjustments and caution with contrast imaging. 5

Contrast-Enhanced CT Considerations:

• Avoid routine contrast-enhanced CT unless there is clinical suspicion of complicated diverticulitis, abscess, or other acute surgical pathology 1

• If CT with IV contrast is deemed essential, the risk-benefit must be carefully weighed, as chronic kidney disease with eGFR ≤45 mL/min/1.73 m² is the most significant predictor of contrast-induced acute kidney injury 1

• Recent evidence suggests the risk of contrast-induced AKI may be lower than previously thought, but caution remains warranted at this GFR level 1

• Alternative imaging includes ultrasound (sensitivity 0.90, specificity 0.90-1.00 for diverticulitis) or unenhanced CT if structural pathology needs exclusion 1

Medication Review:

• Perform comprehensive medication review immediately, as many drugs require dose adjustment at GFR 38 mL/min/1.73 m² 5

• NSAIDs must be avoided or discontinued, as they are nephrotoxic and can worsen renal function and cause diarrhea 5, 6

• Antibiotics (ciprofloxacin, acyclovir, gabapentin, memantine) require dose reduction at this GFR level 5

• Proton pump inhibitors can cause microscopic colitis and should be reviewed 3

Additional Testing if Initial Workup Negative

If colonoscopy with biopsies, coeliac serology, and faecal calprotectin are negative, proceed with bile acid diarrhoea testing. 1

• SeHCAT scan (75-selenium homocholic acid taurine retention test) is the gold standard where available, or serum 7-alpha-hydroxy-4-cholesten-3-one, or faecal bile acid measurement 1

• Bile acid diarrhoea is common, treatable with bile acid sequestrants, and often undiagnosed in elderly patients 1

• Stool studies including culture, ova and parasites, and Clostridioides difficile testing if recent antibiotic exposure or hospitalization 2, 4

• Fecal elastase to assess for pancreatic exocrine insufficiency if steatorrhea is suspected (greasy, floating stools) 2, 4

Clinical Pitfalls in Elderly Patients

Elderly patients with chronic diarrhea present atypically and require heightened clinical suspicion. 1, 3

• Only 50% of elderly patients with acute diverticulitis present with typical abdominal pain, 17% have fever, and 43% lack leukocytosis 1

• Diverticular bleeding is more common in elderly patients than younger cohorts 1

• Do not assume this is IBS-D despite symptom pattern, as Rome IV criteria have only 52-74% specificity and do not reliably exclude organic disease in elderly patients 1

• Functional diarrhea and IBS-D are diagnoses of exclusion and require thoughtful analysis of potential organic causes first 3, 4

Monitoring Strategy

• Repeat eGFR and urinary albumin-to-creatinine ratio (UACR) every 3-6 months given Stage 3b CKD 5

• Consider nephrology referral if eGFR declines >5 mL/min/1.73 m² per year or if proteinuria >1 g/day is detected 7, 5

• Blood pressure should be optimized to <130/80 mmHg if tolerated, with ACE inhibitor or ARB if hypertension and albuminuria ≥30 mg/g are present 5