Evaluation of the Quantum Blue® rapid test for faecal calprotectin

Calprotectin is an acute-phase protein used extensively in the assessment of gastrointestinal inflammation. It can readily be measured by enzyme-linked immunoassay (ELISA) and recently by point-of-care testing (POCT). We evaluated the Quantum Blue(®) POCT in this study and compared it with our existing ELISA method.

The method comparison study used faecal samples (n = 47) sent to the laboratory for routine calprotectin analysis. Linearity was assessed by serial dilution of extracted faeces (n = 4). Extraction efficiency was determined by repeat extraction of three different stools. The variation in results as a consequence of reading the POCT cartridges either side of the recommended 12 min was also assessed.

The assay was linear across the range stated by the manufacturer. When multiple samples were taken from the same stool, results varied from -31.3% to +31.5%. For the clinical arm of our study, strictly applying the 50 μg/g cut-off recommended for both assays as positive for gastrointestinal inflammation, there were four patients where results fell a different side of the clinical cut-off; two patients had results higher by Quantum Blue(®) and two higher by ELISA.

In our hands, the Quantum Blue(®) method was a suitable screening test for excluding inflammatory bowel disease. It may be of value to laboratories wishing to offer calprotectin but who do not have sufficient numbers to warrant ELISA methodology or in 'one stop' gastrointestinal clinics where an immediate result is required.