[Standardization of quantitative measurement of rheumatoid factor]

Recently many automated methods have been developed for a quantitative measurement of rheumatoid factor (RF). As they are widely used, it has been claimed that estimated values of RF are quite different among institutions. Standardization of quantitative measurement of RF is, therefore, required. The subcommittee for standardization of RF of the Ministry of Health and Welfare of Japan, worked from 1988 to 1994 in order to obtain an appropriate national standard of RF and has reached the conclusion that murine monoclonal rheumatoid factor (mRF) would be recommended as a new national standard of RF, which allows new expression of RF value (microgram/ml equivalent to the mRF instead of unit/ml referred to the WHO standard). There are two types of methods widely used for the quantification of RF. The first type is a method of light scattering analysis which is based on interaction of RF with particle-coated or aggregated human IgG (Fc) in nepherometry or turbidimetry, RF being expressed as unit/ml referred to the WHO standard. The second is a radioimmunoassay or an enzyme immunoassay in which RF is expressed as index compared to arbitrary standard. The former expression of RF is recognized to indicate agglutination titer of RF and the latter expresses the concentration of RF. The subcommittee decided to target on the former type of methods because of rapid prevalence with large inter-laboratory variations. The mRF is able to agglutinate proportionally IgG-complex with various features in wide range (x x microgram/ml to more than 1 mg/ml). It can be measured by nepherometry and turbidimetry with sufficient stability. The mRF has no misgivings in present and future supply and in immutability after a century. One of the largest advantages of the use of mRF national standard is expected to be able to eliminate the inter-laboratory variations of RF values which are considered to be mainly derived from different methods of laboratory instruments as well as from biological properties of polyclonal RF. The use of microgram/ml equivalent to mRF instead of unit/ml referred to the WHO standard makes it possible to determine the exact RF value of test serum since the mRF preparation could be adjusted to the best concentration to be requested by any available method of instrument to measure agglutination titer of RF.