Heterophile antibody interference affecting multiple Roche immunoassays: A case study

Preparation and characterization of a homogeneous immunoassay for point-of-care testing (POCT) of procalcitonin (PCT)

Procalcitonin (PCT) has been recognized as a specific and early marker for microbial infection and sepsis. Sensitive measuring interaction-triggered luminescence experiment (SMILE), a homogeneous immunoassay method, was established for point-of-care testing (POCT) of PCT. SMILE is achieved through the principle of double antibody sandwich, where two antibodies immobilized on the surface of polystyrene microspheres (donor and acceptor beads) bind to the PCT antigen. The donor bead contains phthalocyanine dye (luminol chemiluminescent substance) and the acceptor bead contains dimethylthiophene derivatives and Eu chelates. Therefore, singlet oxygen can be transferred when the distance between donor and acceptor beads is within 200 nm, generating detectable luminescent signals. Scanning electron microscopy (SEM) was used to detect the diameter and polymer dispersity index (PDI) of microspheres before and after binding with antibodies to characterize the immobilization of antibodies. The reaction conditions for antibody immobilization including pH, mass ratio and reaction time have also been optimized. The limit of quantitation (LOQ) of the SMILE method (0.01 ng mL-1) was lower than that of the LFI method (0.1 ng mL-1), the working range (0.01-500 ng mL-1) was wider than that of the LFI method (0.1-50 ng mL-1), and the assay time (10 min) was shorter than that of the LFI method (15 min). So, SMILE is more suitable for POCT of PCT compared with lateral flow immunochromatography (LFI), which is the most used measuring method, due to its advantages of simple operation, saving time, convenience, wide detection range, and high sensitivity and accuracy.

False hyperthyroidism caused by interference in immunoassays

Objectives

Immunoassays used to assess thyroid function are vulnerable to different types of interference that may affect clinical decision-making.

Case presentation

We report the case of a 37-year-old woman who developed iatrogenic hypothyroidism after having received radioiode therapy who visited our hospital for her annual checkup. The patient was asymptomatic, without signs suggestive of thyroid disease. However, laboratory analysis proved otherwise: thyrotropin (TSH) 7.75 mU/L, thyroxine (FT4) >7.7 ng/dL.

Conclusions

The inconsistency between her clinical symptoms and the biochemistry data raised the possibility of a methodological interference. A thorough evaluation of the main causes of interference was conducted in the laboratory to exclude the presence of interference in TSH and FT4. Finally, different interfering agents were identified, which affected free thyroid hormone and TSH determination.

Heterophile antibody interference associated with natural killer cell therapy

The adoptive transfer of ex vivo-expanded natural killer (NK) cells has recently been employed as an alternative cancer treatment in certain institutions. However, the safety profiles of this strategy remain uncharacterized. We evaluated three patients who exhibited elevated serum parathyroid hormone (PTH) levels without the relevant clinical manifestations and had a history of autologous NK cell therapy. The serum PTH concentration was measured using a second-generation PTH assay, and the serum thyroglobulin concentration was measured using a second-generation thyroglobulin assay. Subsequently, the PTH or thyroglobulin concentration obtained using heterophile-blocking tube (HBT) for a secondary confirmation assay was measured and compared with the result of the initial assay. The three patients had falsely elevated serum PTH and thyroglobulin levels owing to heterophile antibody interference associated with NK cell therapy that persisted for at least up to 12 months after the treatment and was confirmed by normalization of hormone levels after HBT treatment. We propose that certain types of mouse monoclonal antibodies used to stimulate NK cells can induce heterophile antibodies. Abnormal laboratory test results in individuals administered NK cell therapy without the relevant clinical manifestations must be examined in the context of heterophile antibody interference to avoid misdiagnosis and unnecessary testing.

Glycosylation may influence sex hormone-binding globulin measurements

A discordance between sex hormone-binding globulin (SHBG) measurements by 2-site ELISAs was investigated using pairings of various "in house" SHBG antibodies together with a concordant control. The 2-site monoclonal ELISAs used the same base coat (11F11) and discordance was observed with one top coat monoclonal antibody (7H9) and also when a polyclonal SHBG antibody was paired with the basecoat antibody (11F11). Sialidase treatment of the discordant sample and purified SHBG revealed increased levels using 7H9 whereas there was no change in SHBG in the concordant sample. Conversely, following sialidase treatment, the discordant sample showed no change in SHBG measured using the other monoclonal antibody pairings whereas the SHBG levels in the concordant sample declined following sialidase using the same monoclonal antibody pairings. This implicated glycosylation as a factor in antibody recognition and synthetic peptides spanning the two N-linked and one O-linked glycosylation regions showed that SHBG recognition by monoclonal antibody 7H9 could be disrupted by a peptide spanning the O-linked glycosylation site. Hence rather than immunoassay discordance being attributed to heterophile antibodies or other circulating antibodies here it can be likely attributed to glycosylation affecting antibody recognition and hence the measurement of SHBG.

Characterization of canine anti-mouse antibodies highlights that multiple strategies are needed to combat immunoassay interference

Immunoassays are widely used for detection and quantification of analytes in biological samples, but are vulnerable to analytical errors caused by interfering sample substances. Of particular interest are endogenous anti-animal antibodies that may bind to the immunoassay antibodies and cause erroneous test results. This phenomenon is a hazard to patient safety in both human and veterinary medicine. Here, we demonstrate that anti-mouse antibodies in dogs bind selectively to different regions of the murine IgG molecule, cross-react with IgG from different species, and consist of all major antibody classes present in canine serum (IgA, IgG and IgM). The antibody characteristics varied among individuals and their prevalence differed between two dog breeds. The selective binding to different IgG regions suggests that the antibodies might not originate from immunization through exposure to mice or other species. These findings show that canine anti-mouse antibodies are highly heterogeneous in nature and therefore require a combination of strategies to be counteracted.