A 52-year-old man presents with chronic abdominal pain, steatorrhea, and weight loss over 6 months. Serum amylase and lipase are normal. Clinical suspicion for chronic pancreatitis is high. Which investigation is most appropriate to confirm the diagnosis and assess pancreatic exocrine insufficiency?

Explanation

## Investigation of Choice for Chronic Pancreatitis with Exocrine Insufficiency ### Why Secretin Stimulation Test is Correct **Key Point:** The secretin stimulation test is the gold standard functional test for assessing pancreatic exocrine reserve in chronic pancreatitis. It directly measures pancreatic bicarbonate and enzyme secretion in response to secretin stimulus. **High-Yield:** In chronic pancreatitis: - Serum amylase and lipase are often **normal** (unlike acute pancreatitis) because pancreatic parenchymal destruction is gradual and chronic - Functional tests like secretin stimulation are more sensitive than imaging in early-to-moderate disease - The test shows **reduced bicarbonate concentration** and **decreased enzyme output** in pancreatic insufficiency ### Mechanism of Secretin Stimulation Test Secretin stimulates pancreatic ductal cells to secrete bicarbonate-rich fluid. In chronic pancreatitis: 1. Ductal obstruction and parenchymal atrophy reduce response 2. Bicarbonate output < 20 mEq/L/30 min = abnormal 3. Enzyme output also reduced proportionally ### Comparison with Other Investigations | Investigation | Sensitivity in CP | Specificity | Detects | Limitation | |---|---|---|---|---| | **Secretin stimulation** | 90–95% | High | Functional insufficiency | Invasive, requires duodenal intubation | | Fecal chymotrypsin | 60–70% | Moderate | Severe enzyme deficiency | Only positive in advanced disease | | Serum enzymes | 30–40% | Low | Acute flare-ups | Often normal in chronic disease | | Abdominal ultrasound | 50–70% | Moderate | Structural changes (ductal dilation, calcification) | Misses early/mild disease | **Clinical Pearl:** Fecal chymotrypsin is a screening test; absence suggests pancreatic insufficiency but is insensitive in mild-to-moderate disease. Secretin test is more sensitive and confirms functional reserve. **Tip:** In NEET PG, when the stem mentions **normal serum enzymes + clinical suspicion for chronic pancreatitis**, think **secretin stimulation test** — it is the functional gold standard.