Abstract:

Objective To investigate the interference of monoclonal immunoglobulin（M protein） to immunoglobulin determination by immunoturbidimetry and nephelometry. Methods A total of 25 healthy subjects（healthy control group） and 54 patients with different concentrations and different types of M proteins （20 cases of IgG,16 cases of IgA and 18 cases of IgM） were enrolled. Their serum specimens were collected. IgG,IgA and IgM were determined by immunoturbidimetry and nephelometry. The interference of M protein to the other immunoglobulins was evaluated through interference and recovery experiments. Results The results of IgG,IgA and IgM determinations by nephelometry were higher than those by immunoturbidimetry （P<0.05）. The relative differences of immunoturbidimetry and nephelometry for IgG and IgM determinations in healthy control group were 4.86% and -1.00%,respectively,which were less than allowable total error（TEa）. However,the relative difference for IgA （15.42%） was higher than TEa. For IgG type and IgM type M protein patients,the IgG and IgM results' relative differences between the 2 methods were 14.38% and 4.06%,respectively,which were higher than those in healthy control group （P<0.05）. However,for IgA type M protein patients,the relative difference was 11.95%,which was lower than that in healthy control group （P<0.05）. When IgG level of IgG type M protein was ≥35.13 g/L,the IgA recovery results' difference（Diff%） for IgA was near or over TEa by immunoturbidimetry. When IgG level reached 43.64 g/L,the Diff% for IgM was lower than TEa by immunoturbidimetry. The same level of IgG type M protein did not show obvious interference effect on nephelometry. For immunoturbidimetry,IgA and IgM type M proteins interfered on IgG determination,and the Diff% was higher than IgG corresponding TEa. However,for nephelometry,the relative high levels of IgA and IgM interfered on IgG determination. For either immunoturbidimetry or nephelometry,there was interference of IgA type M protein on IgM determination or IgM type M protein on IgA determination,and their Diff% were higher than IgM and IgA corresponding TEa,respectively. Conclusions IgG,IgA and IgM type M proteins interfere on the other 2 immunoglobulins in same specimens,and the interference depends on M protein level. Nephelometry shows better anti-interference of M protein than immunoturbidimetry.

Key words: Monoclonal immunoglobulin, Nephelometry, Immunoturbidimetry, Immunoglobulin