Between-assay variability of faecal calprotectin enzyme-linked immunosorbent assay kits

BACKGROUND

Faecal calprotectin (f-Cp), a marker of intestinal inflammation, can be used to distinguish between functional and organic bowel disease. F-Cp, following extraction, is commonly quantified using enzyme-linked immunosorbent assays (ELISAs) but there are no data comparing the different f-Cp assays or sample extraction devices. We, therefore, evaluated and compared the performance of the Immunodiagnostik, Bühlmann and Eurospital f-Cp ELISA assays as well as the Roche, Immunodiagnostik and ScheBo Biotech commercial faecal extraction devices. We also briefly report results from a pilot f-Cp external quality assurance (EQA) scheme.

METHODS

Imprecision, linearity, recovery, drift and limit of quantitation of the f-Cp assays were evaluated and between-assay variability assessed. The three commercial sample extraction devices were compared with the manual weighing method. Four faecal samples were distributed as part of a pilot EQA scheme to 15 laboratories using quantitative ELISA f-Cp assays.

RESULTS

The three f-Cp assays demonstrated adequate intra-/interbatch imprecision, linearity and recovery. The cross-comparison study and EQA data demonstrated that, for the same sample, the Bühlmann assay reports up to 3.8 times higher f-Cp concentrations than the Immunodiagnostik and Eurospital assays. On average, the commercial extraction devices led to a 7.8-28.1% under-recovery of f-Cp in comparison to the manual weighing method.

CONCLUSIONS

Laboratories should be aware of the lack of the assay standardization, as demonstrated by the between-assay variability. A comparison between f-Cp concentrations reported by these assays and clinical markers of disease severity is required in order to determine their diagnostic accuracy. The EQA scheme represents the first available programme for f-Cp.

Local anaesthetics

Although there are two types of LA, amides are now more commonly used. Understanding the pharmacology and physicochemical properties of LAs enables prediction of speed of onset, duration of action and determination of the correct LA for a particular clinical requirement. Drug concentration is expressed as a percentage such that 1% = 1 g/100 ml = 1,000 mg/100 ml = 10 mg/ml. Lipid rescue therapy has been shown to be a very effective treatment for LA toxicity.