Falsely Increased Nephelometric. ResuftsCausedby a Monoclonal. Rheumatoid. Factor. To the Editor: Plasma proteins can be quantified for diagnostic purposes ...
tively high) value at all three examinations (tracking). To avoid misinterpretations, this variation with age should be considered when erythrocyte protoporphyrin concentrations are used to screen infants for anemia caused by iron deficiency (1).
References 1. Yip R, &hwartz S, Deinard AS. Screening for iron deficiency with the erythrocyte protoporphyrin test. Pediatrics 1983;72: 214-9.
2. Schwartz 5, Stephenson B, Sarkar D, Freyholtz H, Ruth G. Quantitative assay of erythrocyte “free” and zinc-protoporphyrin: clinical and genetic studies. mt J Biochem 1980;12:1053-7. Axel Brock Univ. of Aarhus Dept. ofClin. Chem. Randers Hospital DK 8900 Randers, Denmark Kim Fleischer
Michaelsen
Univ. of Copenhagen Dept. of Pediatrics Hvidovre Hospital DK 2650 Hvidovre, Denmark
identified
Nephelometric ResuftsCausedby a Monoclonal Falsely Increased Rheumatoid
Factor
To the Editor:
Plasma proteins can be quantified for diagnostic purposes by various dif-
ferent
immunological
techniques.
Among these, nephelometry and turbidimetry have been increasingly used, owing to their advantages of rapid performance and possible automation.
Usually
the
degree
suits for tests of her serum at admission gave an unusually high value for CRP, measured by latex nephelometry with polystyrene latex particles coated with rabbit anti-CRP IgG (Table 1). Her concentrations of C3c, C4, IgG, IgA, and 1gM, measured by liquidphase nephelometry with rabbit antisera, were also increased. For the nephelometric assays we used a Behring Nephelometer Analyzer (fixed time mode; Behringwerke AG, Marburg, F.R.G.). The titer of RF, determined by agglutination ofgelatin partides coated with denatured rabbit IgG (RAPA test; Fujirebio Inc., Tokyo, Japan), was extremely high: 1:3.2 x lob (normal reference value,
