Analytical Performance and Clinicopathologic Correlation of Four Fecal Calprotectin Methods

Leonie P. J. Pelkmans, PhD; Monique J. M. de Groot, PhD; Joyce Curvers, PhD

Disclosures

Am J Clin Pathol. 2019;152(3):392-398. 

In This Article

Abstract and Introduction

Abstract

Objectives: Calprotectin is a noninvasive biomarker that can distinguish inflammatory bowel disease from irritable bowel syndrome. We investigated four automated fecal calprotectin methods on five different platforms for their preanalytical process, analytical performance, and clinicopathologic correlation.

Methods: Four calprotectin methods (Bühlmann, EliA CN, EliA CN2, and DiaSorin) were performed on five platforms (Cobas 8000 E502, Phadia Immunocap 100 and 250, and Liaison and Liaison XL) in two hospital laboratories.

Results: Overall variation for the different extraction devices was less than 19% when feces were of normal consistency. Freeze-thawing of samples resulted in comparable results compared with fresh samples. The different methods had a good analytic correlation (R = 0.83–0.95). Their clinicopathologic correlation was comparable, but the Bühlmann method showed significantly higher calprotectin values in every patient category.

Conclusions: The automated calprotectin methods showed a good performance and comparable clinicopathologic correlation. Due to lack of standardization, the numerical values differ for the various methods.

Introduction

Calprotectin is a calcium binding protein that belongs to the S-100 protein family. It is mainly present in neutrophils and monocytes and has regulatory functions in the inflammatory process. Furthermore, it appears to have antimicrobial and antiproliferative properties.[1] Calprotectin in feces is an important noninvasive biomarker that can distinguish inflammatory bowel disease (IBD) from irritable bowel syndrome (IBS).[2] Both diseases are characterized by similar signs and symptoms. Therefore, it is difficult to distinguish the diseases purely based on clinical features.[3,4] In patients with IBD, however, inflammation of the bowel is typically seen, while this is absent in patients with IBS. The inflammation causes an increased permeability of the mucosa, which leads to an increased migration of granulocytes and monocytes to the gut lumen.[1] This leads to increased levels of fecal calprotectin in patients with IBD. In addition, calprotectin is used to measure disease activity, predict relapse, and monitor therapy response.[2] However, calprotectin levels can also be increased by other diseases or infections of the gastrointestinal tract, including bacterial dysentery, gastric cancer, colorectal adenoma, and cancer.[1,5]

It has been demonstrated that calprotectin has a good negative predictive value.[6]Hence, a result for calprotectin in feces below the upper limit of normal (50 μg/g for most methods) rules out the presence of IBD. The golden standard to diagnose IBD is an ileoscopy with biopsies.[7] Endoscopy is an invasive, costly technique that is uncomfortable for the patient. Calprotectin measurement can be used as a screening tool for endoscopy since it can distinguish IBD and IBS. Thus, screening for calprotectin in feces is a cost-effective strategy, saving money and discomfort. A meta-analysis[5] showed that fecal calprotectin screening of adults with suspected IBD could reduce the number of adults requiring endoscopy by 67%. Calprotectin is recommended as a tool to differentiate between IBD and IBS by the American College of Gastroenterology[8] and the British Society of Gastroenterology,[9] among others.

There are several commercial semiautomated methods to measure calprotectin levels in feces. Previous enzyme-linked immunosorbent assay methods are sensitive, but it is a very time-consuming technique and therefore less suitable for large amounts of samples in routine use. Point-of-care testing is an easy and quick method, but this is also less suitable for a large number of samples since the processing of the feces needs to take place immediately before analysis. Moreover, semiquantitative point-of-care testing is not suitable for follow-up. Automated methods currently available include fluorescence enzyme immunoassays, chemiluminescence immunoassays, and particle-enhanced turbidimetric immunoassay. Turnaround times are minimized by these assays, but it is still necessary to extract the calprotectin protein from the feces before it can be measured.

The golden standard for extraction is the weighing method, but again this is very time-consuming. Therefore, several commercial extraction devices have been introduced. Importantly, various studies have shown that extraction of calprotectin from a stool sample can result in different calprotectin values when different extraction methods are used and the calprotectin extracts are measured on the same platform.[10–13] The extent of variation when multiple extracts are generated from one stool sample with the same extraction method is not described in literature.

In this study, we compared four automated methods (Bühlmann, EliA CN, EliA CN2, and DiaSorin) on five platforms (Cobas 8000 E502, Phadia Immunocap 100 and 250, and Liaison and Liaison XL) in two laboratories for their analytical performance and clinicopathologic correlation. Furthermore, we evaluated the preanalytical process by investigating the variability of the sampling and the influence of freeze-thawing.

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