Heterophilic antibody interference

Another form of random matrix-related interference is more rarely occurring gross errors, which typically are seen in the context of immunoassays and relate to unexpected antibody interactions (see interference section) Such an error will usually show up as an outlier in method comparison studies. A weU-known source is the occurrence of heterophilic antibodies. This is the background for the fact that outliers should be carefuUy considered and not just discarded from the data analysis procedure. Supplementary studies may help clarify such random matrix-related interferences and may provide specifications for the assay that limit its application in certain contexts (e.g., with regard to samples from certain patient categories). 

Other technical problems, such as heterophilic antibody (HAMA) interference, may limit the clinical value of Tg measurements. Recommendations regarding approaches to standardization, precision, limits of detection, and hook effects have been suggested. Serum Tg values obtained by different methods are usually not interchangeable, and the same assay should be used to perform serial serum Tg measurements in a patient. When a change in method is made, the laboratory should define performance characteristics of the new method and validate its clinical utility before implementing the method for patient care. 

FIGURE 3.2 ELISA interference. Matrix components such as proteolytic enzymes, binding proteins, comedication, or heterophilic antibodies may cause interference through interaction with the analyte and/or the antibodies used in the system. Incubation time, temperature, and light among other factors can affect the formation of colored product. 

FIGURE 3.6 (a) Example of interference due to heterophilic antibody in an assay where a... 

Detection and Measurement of Interference Due to Heterophilic Antibodies Often, a method is used to quantify an endogenous analyte associated... 

Perform a bridging assay in which the same antibody is used as both capture and detector antibody. If the assay signal in a predose sample is increased above the capture or detector antibody blank signal, interference should be suspected an increase in signal indicates likely presence of heterophilic antibodies cross-linking... 

Preincubation of the study samples with animal antibodies or serum has been reported to substantially decrease positive interference due to heterophilic antibodies by preventing, for example, heterophilic human antimouse antibodies present in the study samples from cross-linking the reagent antibodies [37,39]. These types of reagents are produced commercially for such purposes. 

Warren, D.J., Bjemer, J., Paus, E., Bprmer, O.P., and Nustad, K. (2005) Use of an in vivo biotinylated single chain antibody as capture reagent in an immunometric assay to decrease the incidence of interference from heterophilic antibodies. Clinical Chemistry, 51, 830 838. 

Nonspecific nonspecificity results from interference of matrix components that are structurally unrelated to the analyte of interest. Examples of such interfering matrix components would include serum proteins, lipids, heterophilic antibodies, rheumatoid factor, proteases, and so on. Nonspecific nonspecificity is often referred to as matrix effect. Figure 4.3 depicts the impact of matrix on the assay performance. Matrix interference is one of the chief reasons that LB As often require more method development and validation prior to switching from one species matrix to another or even within the same species. In addition, we recommend during clinical study support that matrix from the relevant disease populations be tested for matrix effects as soon as that matrix becomes available. Matrix effects should be evaluated by comparing the concentration response relationship of both spiked and unspiked samples of the biological matrix (recommendation is 10 or more lots of individual sources) to a comparable buffer solution. It is recommended that the spiked sample... 

Interference Native inhibitors, anti-cytokine antibodies Serum proteins, anti-cytokine and heterophile antibodies, rheumatoid factors... 

Immunoassays established to measure the very low (ng/ml) concentrations of cytokines in body fluids are uniquely susceptible to nonspecific interference from plasma or serum and from interfering antibodies or proteins that may cross-react with those used in the assay. Rheumatoid factors are well known to cause interference in solid phase assays such as ELISA (B8). Heterophile antibodies that react with animal immunoglobulins present a problem in assays in which serum or plasma is used at low dilution (V8) (Table 7). Serum contains a complement, which may interfere with solid phase immunoassays unless inactivation has taken place (B55). In designing assays controls must be employed to test for these effects... 

False negative results for cTn may occur if the assay is insufficiently sensitive, especially in enzyme-linked immunosorbent assay (ELISA) methods where colorimetry rather than fluorescence or chemiluminescence is used as the detection method, and in those assays with poor cross-species reactivity. False negative results may also occur in samples that have deteriorated. Serum cTn is stable at -70°C, but it deteriorates several percent per day at 4°C and by 10% per week at -20°C. Rare false positive results may occur with circulating heterophilic antibodies, fibrin clots, or incomplete serum separation (or in the presence of rheumatoid factor). Hemolysis produces negligible interference. 

Interference with diagnostic tests A patient who was given muromonab after renal allograft developed human antimurine heterophil antibodies, causing a falsely raised parathormone measurement [136 ]. 

---