Heterophilic antibody interference in a tryptase immunoassay.

Objective: Investigation of the susceptibility of a tryptase immunoassay to interference by heterophilic antibodies.

Methods: The effect of preincubation with a blocking agent was investigated on the levels of tryptase, human anti-mouse antibodies and IgM rheumatoid factor in sera with elevated IgM rheumatoid factor levels.

Results: In 5 of 30 sera with IgM rheumatoid factor, tryptase levels were reduced at least twofold after pre-incubation with blocking reagent.

Serum creatinine and the DuPont dimension: possible improvements.

A study is reported on the determination of creatinine with the DuPont Dimension, paying special attention to interference by bilirubin. Various methods for dealing with bilirubin interference are described, including modification of the Jaffé reaction, enzymatic assay of creatinine, enzymatic destruction of bilirubin, and ultrafiltration of the serum sample. None of these modifications gave completely satisfactory results, although the Jaffé method with a ferricyanide oxidation step, and the enzymatic assay with ferrocyanide gave reasonable results with icteric specimens from adult patients, while only the latter method could be used for neonatal serum samples.