Immunoglobulin G-Rheumatoid Factor Interferes Negatively with Serum Hepatitis B Envelope Antigen Chemiluminescent Microparticle Immunoassay.

Abstract

Rheumatoid factor (RF) can interfere both positively and negatively in immunoassays. It remains unclear whether the negative interference is an exceptional phenomenon or a denominator of immunoassays and which RF subgroup plays a key role in its causation. Serum models comprising hepatitis B envelope antigen (HBeAg) and RF were made by blending HBeAg-positive sera and RF-positive sera at a ratio of 1:9. Paramagnetic microparticles coated with P human chorionic gonadotropin (betaHCG)-anti-betaHCG complexes were used to remove RFs from the models, and HBeAg was determined in models using the chemiluminescent microparticle immunoassay (CMIA). HBeAg sample/cutoff (S/CO) relative light units (RLUs) measured in 27.06% of the serum models were significantly lower than those in the control models with a maximum decline rate of > 70.00%. The discrepancies between the HBeAg S/CO RLUs measured in serum and control models were not associated with the serum RF levels when these ranged from 20 to 1510 IU/mL. Pretreatment of the serum models with the paramagnetic microparticles increased the HBeAg S/CO RLUs measured and decreased the immunoglobulin (Ig) A-RF and IgG-RF levels significantly. However, the discrepancies between the HBeAg S/CO RLUs measured in serum models before and after pretreatment were only associated inversely with the discrepancies in IgG-RF levels. Measurement of HBeAg by CMIA is susceptible to negative interference from RFs. The level of IgG-RF played a key role in interfering with HBeAg CIMA and predominantly caused falsely low results. The pretreatment of samples with blocking reagents is therefore advisable prior to the interpretation of test results.