How should different calprotectin values be interpreted by the clinician?
Many European gastroenterologists have used our ELISAs for many years, and I think the recommendations below are representative for a clinical practice that is adopted by many clinicians. The patients are divided into two groups; the evaluation of test results is different in the two groups.
Group 1: This is undiagnosed patients with stomach problems; clinical examination cannot exclude IBD. The cut-off value is 50 mg/kg, but values between 50 and 100 are often seen without endoscopic findings. They can be characterized as false positives or lying in a grey zone. Fecal calprotectin should be repeated and clinical parameters considered. Values higher than 100 are always taken as positive.
Group 2: This is patients with IBD. Calprotectin values of several hundreds or thousands are seen in patients with active IBD, reflecting the disease activity objectively. By repeated testing, every week or month, the marker is very useful in monitoring the effect of treatment in active iBD. If high calprotectin levels are not reduced during treatment, non-responders can be identified and the medication adjusted accordingly. During effective treatment a steep fall in the calprotectin curve is usually seen; when values pass 200 or possibly 150 mg/kg and persist below that level, this indicates mucosal healing, which can be verified by endoscopy, and the treatment can be stopped. Increasing values passing 150/200 mg/kg indicate relapse and treatment should again be considered.
Calprotectin levels between 150/200 and 500 mg/kg indicate “moderate disease activity” and values above that “high disease activity”.
The conclusion so far is that in patients with clinical quiescent disease and calprotectin levels below 150/200 treatment is not necessarily needed. However, it is important to bear in mind that the cut off values mentioned above are only indicative, and hopefully ongoing studies will elucidate this important issue more precisely. Fecal calprotectin is an objective marker of disease activity in IBD, but although not decisive, it should be taken into consideration as an important factor to achieve optimal decisions on treatment of patients with IBD.
In most biological quantitative tests there are “grey zones” or “border zones” in which the interpretation of results are questionable; it is favourable to make these zones as narrow as possible. In CalproLab and Calpro Calprotectin ELISA this objective is achieved; the grey zone in group 1 is in fact only from 50 to 100 mg/kg. In contrast, test kits from manufacturers that measure 2 or 3 times higher than that of CalproLab and still maintain 50 mg/kg as the cut off value, have a problem: the wide grey zone makes the interpretation of results difficult, necessitating retesting of many samples.
Our CalproLab assay has one of the broadest measuring ranges, from 25 to 2500 mg/kg with only one dilution of the fecal extracts, in the market. Retesting using alternative dilutions is therefore seldom necessary.
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Li XG, Lv YM, Gu F, Yang XL., Department of Gastroenterology, Peking University Third May 9, 2015
The PhiCal Test has now been approved by the FDA for clinical use in the USA October 1, 2014
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