Is a stool sample for a fecal calprotectin assay stable enough to be refrigerated and delivered to Quest Diagnostics on a Friday, or should it be collected and submitted on Monday?

Stool Sample Stability for Fecal Calprotectin Testing

Refrigerate the stool sample immediately and deliver it to Quest Diagnostics on Friday—calprotectin degrades significantly at room temperature within 24-48 hours, leading to falsely low results that may cause undertreatment.

Storage Temperature is Critical

The British Society of Gastroenterology explicitly recommends that stool samples be stored for no more than 3 days at room temperature before analysis, but this guideline predates more recent stability data showing faster degradation. 1

More recent research demonstrates that room temperature storage causes rapid calprotectin degradation:

• After just 1 day at room temperature, calprotectin concentrations decline significantly from baseline (p < 0.001), with mean declines reaching 30-60% by day 4 depending on the assay used. 2
• After 6 days at room temperature, mean calprotectin concentrations drop by 35% in untreated stool samples. 3
• Refrigeration at 4°C significantly preserves calprotectin stability compared to room temperature storage (p = 0.0066). 3

Practical Recommendations for Your Patient

For Friday delivery:

• Collect the first morning stool (this minimizes day-to-day variability). 1
• Refrigerate immediately at 4°C after collection and keep refrigerated until delivery. 3, 2
• Deliver to Quest Diagnostics on Friday as planned—refrigerated samples remain stable for at least 4 days. 2

If refrigeration is not possible:

• Deliver the sample within 24 hours of collection to minimize degradation. 2
• Be aware that even short delays at room temperature may produce falsely low results. 3, 2

Clinical Significance of Degradation

The stability issue has direct clinical consequences:

• Children with IBD may be "falsely reassured by low calprotectin values" when samples degrade at room temperature, potentially leading to undertreatment. 3
• The rate of decline varies between different calprotectin assays (30-60% decline after 4 days), making standardized pre-analytical handling essential. 2
• Extracted feces in assay-specific extraction buffer also degrades at room temperature, with 46% mean decline after 6 days. 3

Why Monday Collection is Unnecessary

Refrigerated samples are stable for several days:

• Calprotectin in untreated feces stored at 4°C does not show significant decline from baseline until after 4 days of storage. 2
• One older study reported stability for up to 7 days at room temperature, but this conflicts with multiple recent studies showing degradation within 1-2 days—the more recent evidence should guide practice. 4, 3, 2

Common Pitfalls to Avoid

• Never allow the sample to sit at room temperature for more than 24 hours—this produces clinically significant false-negative results. 3, 2
• Do not assume all laboratories process samples immediately—weekend delivery may mean the sample sits until Monday, making refrigeration during transport essential. 2
• Avoid freeze-thaw cycles if the patient attempts to freeze the sample—this is not recommended for routine calprotectin testing. 1

Bottom Line

Instruct your patient to refrigerate the stool sample immediately after collection and deliver it to Quest Diagnostics on Friday while keeping it cold during transport. This approach ensures accurate results without unnecessary delay in diagnosis or treatment decisions. 3, 2