Table 1

Characteristics of enzyme immunoassays used to detect isotypes of rheumatoid factors (RF)

RF isotype(s) detectedOrigin of assayAntigen (as presented by the manufacturers)Number (range) of calibratorsSample dilutionsCut off value (positive when)
*No information available about antigen preparation; †example of concentration(s).
IgM, IgG, and IgAImmcoRabbit IgG*1 (136 EU/ml)†201>20 EU/ml
IgMImmcoRabbit IgG*4 (6–50 IU/ml)†101>9 IU/ml
IgMSigmaInactivated affinity purified human IgG4 (0–50 IU/ml)†21≥6 IU/ml
IgMDiamedixPurified human IgG1 (100 IU/ml)†101≥20 IU/ml
IgMInovaRabbit IgG*5 (6.25–100 IU/ml)101>6 IU/ml
IgMOur laboratoryAffinity purified human IgG Fc fragment13 (0.005–19 IU/ml)25, 50, 100≥10 IU/ml
IgMOur laboratoryAffinity purified rabbit IgG Fc fragment13 (0.005–19 IU/ml)25, 50, 100≥10 IU/ml
IgAImmcoRabbit IgG*4 (21–167 EU/ml)†101>25 EU/ml
IgAInovaRabbit IgG*5 (6.25–100 U/ml)101>6 U/ml
IgAOur laboratoryAffinity purified human IgG Fc fragment13 (0.001–6 U/ml)25, 50, 100≥10 U/ml
IgAOur laboratoryAffinity purified rabbit IgG Fc fragment13 (0.001–6 U/ml)25, 50, 100≥10 U/ml