Validation of a multiplex chip-based assay for the detection of autoantibodies against citrullinated peptides

Table 2 Performance of the 12 investigated citrullinated peptides

Peptide	Percentage of RA sera reacting with the individual citrullinated peptides^a (%) at 98.0% specificity	Number of positive patients/number of CCP2-positive patients (%)^a	Percentage of RA sera reacting with the individual citrullinated peptides (%) at 98.0% specificity after arginine subtraction^b	Number of positive patients/number of CCP2-positive patients (%)^b after arginine subtraction	Positive (+) or negative (-) effect of arginine subtraction on the diagnostic performance
Eno5-21 (CEP-1)	39.4	91.0	40.9	94.5	+
Vim60-75	31.9	73.7	40.0	92.4	+
Vim2-17	10.8	24.9	8.0	18.5	-
Fil307-324 (CCP1)	32.8	75.8	32.5	75.1	-
Fibβ36-52	45.2	104.4	41.9	96.8	-
Fibβ563-583	31.0	71.6	31.5	72.7	+
Fibβ580-600	10.5	24.2	9.8	22.6	-
Fibβ62-81a	19.8	45.7	20.6	47.6	+
Fibβ62-81b	28.0	64.7	26.1	60.3	-
Fibβ60-74	38.8	89.6	37.3	86.1	-
Fibα621-635	25.9	59.8	29.0	67.0	+
CII 359-369 (CitC1)	18.8	43.4	ND^c	ND^c	ND^c

Peptides names are designated as in Table 1.
^aThese percentages should be compared with the fact that 43.3% of all RA patients in the present selection of EIRA patients were anti-CCP2 positive.
^bFluorescence intensities for the arginine control peptides were subtracted from the fluorescence intensities for each measurement among RA patients and controls, whereupon the performance was calculated on the net values.
^cNo subtraction was done for this peptide as the arginine control peptide is itself an autoantigen with conformational epitopes that are destroyed by citrullination [20].

ISSN: 1478-6362