What is the role of faecal calprotectin in diagnosing acute diarrhoea illness?

Role of Faecal Calprotectin in Diagnosing Acute Diarrhoeal Illness

Faecal calprotectin is a valuable biomarker in acute diarrhoeal illness that can help distinguish between bacterial and viral causes, with significantly higher levels typically seen in bacterial infections compared to viral gastroenteritis. 1, 2, 3

Diagnostic Value in Acute Diarrhoea

Differentiating Bacterial from Viral Causes

• Faecal calprotectin levels are significantly elevated in bacterial gastroenteritis compared to viral gastroenteritis, with bacterial infections showing median values of 765-1870 μg/g versus 89-95 μg/g in viral infections 1, 2
• Using a threshold of 710 μg/g, faecal calprotectin demonstrates 88.9% sensitivity and 76.0% specificity for identifying bacterial gastroenteritis 1
• Calprotectin shows higher correlation with bacteriologically positive infectious diarrhoea compared to other fecal markers like lactoferrin and fecal occult blood tests 3

Correlation with Disease Severity

• Faecal calprotectin concentrations correlate with clinical severity in infectious diarrhoea, with higher levels seen in severe (843 μg/g) and moderate (402 μg/g) disease compared to mild disease (87 μg/g) 2
• Serial measurements can provide information for disease management and monitoring of the clinical course 2

Practical Considerations for Sample Collection

Proper Collection Technique

• The British Society of Gastroenterology recommends using the first stool passed in the morning for sampling 4
• Samples should be stored for no more than 3 days at room temperature before analysis to maintain stability 4
• Variability exists between different assays, and there can be day-to-day variation in levels from the same patient 4

Potential Confounding Factors

• NSAID use in the past 6 weeks can affect calprotectin levels and should be considered when interpreting results 4, 5
• Other causes of raised calprotectin include colorectal cancer and non-steroidal anti-inflammatory drugs 4

Clinical Applications in Acute Diarrhoea

Screening Tool in Acute Settings

• Faecal calprotectin can generate results within hours to support presumptive diagnosis of infectious diarrhoea, which can help determine suitability of stool samples for culture 3
• As a screening test, it may potentially improve the management algorithm for patients with acute diarrhoea 3

Limitations in Infectious Diarrhoea

• The Infectious Diseases Society of America notes there are insufficient data available to make a recommendation on the value of fecal calprotectin measurement in people with acute infectious diarrhea 4
• While calprotectin is elevated in infectious gastroenteritis, interpretation must always consider the clinical history and symptoms specific to each patient 6

Comparison with Other Diagnostic Approaches

Advantages Over Traditional Methods

• Faecal calprotectin is a non-invasive, easily and rapidly measured laboratory test that can be used alongside simple microscopic examination of stool 1
• It provides higher sensitivity (83%) and specificity (87%) for bacterial diarrhoea compared to fecal lactoferrin (78% sensitivity, 54% specificity) and fecal occult blood test (38% sensitivity, 85% specificity) 3

Integration with Other Diagnostic Tests

• Stool culture remains the gold standard for definitive diagnosis of bacterial pathogens, but calprotectin can help prioritize which samples should undergo culture 3
• Molecular techniques are generally more sensitive than culture for pathogen identification, but calprotectin can provide complementary information about the inflammatory response 4

Common Pitfalls and Caveats

• Faecal calprotectin is not specific for infectious causes and can be elevated in other inflammatory conditions affecting the gut 6, 7
• Different assays may have different optimal cut-off values, which can affect interpretation 7
• A single measurement may not be sufficient for clinical decision-making, and serial measurements may be more informative 2
• The European Society of Gastrointestinal Endoscopy recommends faecal calprotectin primarily for diagnosing and monitoring inflammatory bowel disease rather than acute infectious diarrhoea 5