Introduction Faecal calprotectin (FC) has recently become widely used to differentiate between IBS and IBD following NICE diagnostic guidelines (DG11). There are a number of different assays in use throughout the UK using different extraction methods. We have evaluated a newly introduced Quanta-Lite FC assay (Werfen Ltd, UK) with Eurospital (ES) extraction tubes and compared it to our routine Buhlmann assay with Calex extraction tubes.
Methods All samples were received <72 hrs from collection and frozen upon receipt. The samples, a mixture of both primary and secondary care requests, were thawed at 2–8oC overnight then equilibrated to room temperature for 60 minutes before extraction. The same 76 faecal samples were extracted initially using the Bühlmann Calex tubes and then the ES extraction tubes. FC was then measured using the different ELISA methods on the DS2 ELISA platform.
Results The Calex and ES extraction tubes use 10 and 60 µg/µl of faecal sample respectively. After sampling homogenisation and centrifugation is only required with the Calex tubes whereas the ES tubes require a further step of 20 minutes on the roller mixer. Calex tubes can be loaded directly on the DS2 analyser, whereas the ES tubes require transfer of the supernatant to a secondary tube. The equation of correlation was Buhlmann =0.27 Werfen + 6.6, r2 = 0.813 hence the Buhlmann assay results are on average 3.0 times higher than the Werfen assay. At present within our laboratory Buhlmann results of >49 ug/g are categorised as abnormal (A) and a referral to Gastroenterology is suggested. The Werfen assay reports results of <50 ug/g as normal (N), 50–120 ug/g as borderline (B) with re-testing in 4–6 weeks suggested and >120 ug/g as A. The Buhlmann method states an elevated level of between 50–200µg/g may represent mild disease. The assays categorised the 76 samples as follows: Buhlmann, N 40.8% and A 59.2% and Werfen N 61.8%, B 19.7%, A 18.4%. With the current interpretation 59% of the samples analysed by the Buhlmann method were abnormal whereas 18% of samples tested with the Werfen kit were deemed abnormal. In order to have better interpretative agreement between the assays a borderline range with the Buhlmann assay should be 159 ug/g to 415 ug/g and positive >415 ug/g.
Conclusion In conclusion the Calex tubes are easier to use than the ES tubes: they utilise a smaller sample size; requires less pre-analytical steps; and do not require an additional sample transfer which often resulted in splashing of the extracted faeces. The assays had poor overall diagnostic agreement for the samples tested. Different cut-offs should be used for each assay in order to have a comparable interpretation. Each assay should be assessed in relation to clinical outcome prior to use. We also recommend that the FC method used is reported with the result.
Disclosure of Interest None Declared
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