Rheumatoid Factor and Its Interference with Cytokine Measurements: Problems and Solutions

Table 3

Cytokine concentration in nonprecipitated and PEG-precipitated plasma samples with low RF (P1) and high RF (P4) and synovial fluid samples with low RF (SF1) and high RF (SF4) as well as sensitivity for the assay and ratio between concentrations in nonprecipitated and precipitated samples for IL-1β, IL-4, IL-6, and IL-8 (Spiked with 417 pg/mL. Recovery consistent and as given by manufacturers).

		Concentration pg/mL nonprecipitated	Concentration pg/mL precipitated	Ratio precipitated : nonprecipitated	Baseline concentration nonprecipitated/precipitated pg/mL
IL-1β sensitivity: 10.5 pg/mL	P1	369	272	0,737	0/0
	P4	290,5	220	0,757	1.5/0
	SF1	169	219	1,296	0/0
	SF4	259	270	1,042	0/0
IL-4 sensitivity: 27 pg/mL	P1	334	271	0,811	0/0
	P4	309,8	245	0,791	0.2/0
	SF1	336	292	0,869	0/0
	SF4	337,6	355	1,052	3.4/0
IL-6 sensitivity: 11.5 pg/mL	P1	368	290	0,788	0/0
	P4	477,4	290	0,607	2.6/0
	SF1	293	289	0,986	43/58
	SF4	362	386	1,066	96/115
IL-8 sensitivity: 14.0 pg/mL	P1	280	225	0,804	0/0
	P4	355,8	275	0,773	9.2/0
	SF1	306	296	0,967	54/29
	SF4	387	398	1,028	88/42