Fecal Calprotectin & Hyperinflammation Markers: IBD vs. IBS, and When Ferritin >10,000 Is a Diagnosis

 

Fecal Calprotectin & Hyperinflammation Markers: IBD vs. IBS, and When Ferritin >10,000 Is a Diagnosis

The stool test that saves your patient a colonoscopy and the serum ferritin level that means macrophage activation, not iron overload.

Part 1: Fecal Calprotectin—IBD vs. IBS

Fecal calprotectin is a neutrophil-derived protein released into the gut lumen during intestinal inflammation. It's the single best non-invasive test for distinguishing inflammatory bowel disease (IBD) from irritable bowel syndrome (IBS)—a distinction that saves patients from unnecessary colonoscopies and saves the healthcare system significant cost.

How to Use It

• Calprotectin <50 µg/g: IBD very unlikely. Supports IBS or functional GI disorder. Negative predictive value >95%.
• 50–150: Borderline. Repeat in 4–6 weeks. If persistently elevated, refer for GI evaluation.
• >150: Intestinal inflammation likely. Correlate with clinical picture. Refer for colonoscopy/endoscopy to differentiate Crohn's, UC, or other causes.
• >250: Strongly suggestive of active IBD.

Also useful for monitoring IBD activity: rising calprotectin in a known IBD patient may predict relapse before symptoms appear, enabling preemptive treatment adjustment.

Pitfalls

• NSAIDs cause intestinal inflammation and elevate calprotectin—stop NSAIDs for 2 weeks before testing.
• PPIs may mildly elevate calprotectin in some patients.
• GI infections (bacterial gastroenteritis) elevate calprotectin—test after the infection resolves.
• Colorectal cancer can elevate calprotectin—an elevated result in an older patient still warrants colonoscopy.
• Children <4 years have physiologically higher calprotectin levels; use age-adjusted thresholds.
• Celiac disease can mildly elevate calprotectin.

Part 2: Hyperinflammation Markers—When Ferritin Tells a Different Story

Ferritin as a Hyperinflammation Marker

In the iron studies post, we discussed ferritin as an acute-phase reactant that masks iron deficiency. But extremely elevated ferritin (>1,000–10,000+) is a different diagnostic entity—it signals macrophage activation and hyperinflammation, not iron overload.

Ferritin >10,000 = Think MAS or HLH

Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are life-threatening hyperinflammatory conditions where macrophages go into overdrive, phagocytosing blood cells and releasing massive cytokines. Ferritin >10,000 ng/mL is a classic diagnostic clue (sensitivity ~90% for HLH in children). Other features: high fevers, cytopenias, hepatosplenomegaly, elevated triglycerides, low fibrinogen, elevated soluble IL-2 receptor. MAS is the rheumatologic variant, most commonly complicating systemic JIA (children) or Adult-onset Still's disease.

Adult-Onset Still's Disease

Ferritin >1,000 (often >5,000–10,000+) in a young adult with quotidian (daily spiking) fevers, evanescent salmon-colored rash, arthritis, sore throat, and leukocytosis is Adult-onset Still's disease until proven otherwise. A unique feature: the glycosylated ferritin fraction drops to <20% (normal >50%), which helps confirm the diagnosis. This specialized test isn't available everywhere but is highly specific when obtainable.

Other Hyperinflammation Markers

• Soluble IL-2 receptor (sIL-2R/sCD25): Markedly elevated in HLH/MAS. Included in the HLH-2004 diagnostic criteria.
• Lactate dehydrogenase (LDH): Elevated in hemolysis, tissue destruction, and hyperinflammatory states. Non-specific but part of the pattern.
• Triglycerides: Paradoxically elevated in HLH/MAS (cytokine-mediated lipolysis suppression).
• Fibrinogen: Low in HLH/MAS (consumed by DIC-like process), which is the opposite of what you'd expect in inflammation (fibrinogen is normally an acute-phase reactant that rises).

Bottom Line

Fecal calprotectin is your primary care tool for distinguishing IBD from IBS non-invasively—a negative result (<50) has >95% NPV for ruling out IBD. Stop NSAIDs before testing. On the hyperinflammation side, learn to recognize the pattern: ferritin >10,000 + cytopenias + fevers + hepatosplenomegaly = HLH/MAS until proven otherwise. These are rare but lethal conditions where early recognition saves lives.

Stay sharp out there.