Table 3.
Troubleshooting the most frequent types of immunoassay interference
| Interference type† | Error type | Identification | Troubleshooting |
|---|---|---|---|
| Method-specific interference | |||
| Biotin | Competitive assay: ↑ Sandwich assay: ↓ |
Patient’s file Adsorption if validated Dilution |
Withdraw biotin if possible, and obtain a new sample Test with an alternative method |
| Anti-streptavidin antibody | Competitive assay: ↑ Sandwich assay: ↓ |
Adsorption if validated | Test with an alternative method |
| Signal-specific antibody interference (anti- ruthenium, anti-alkaline phosphatase) | Competitive assay: ↑ Sandwich assay: ↓ |
Alternative method comparison | Alternative method needed |
| Fluorescence signal | ↑ or ↓ | Fluorescein injection | Obtain a new sample after washout |
| Alkaline phosphatase label | ↑ or ↓ | Recombinant alkaline phosphatase therapy | Obtain a new sample after washout, if possible |
| Common interference | |||
| Hook effect (prolactin, HCG, Tg, calcitonin) | ↓ | Progressive dilutions | Two coherent successive dilutions |
| Cross-reaction | Competitive assay: ↑ Sandwich assay: ↑ or ↓ (depending on specificity characteristics) | Patient’s file, therapeutic information | Appropriate interpretation LC-MS/MS control (steroid assays) |
| Macro analyte (prolactin, TSH, FSH, LH) | ↑ | PEG precipitation Recovery test Gel filtration chromatography |
Appropriate interpretation and percent recovery post-PEG |
| Anti-insulin Ab (insulin assay) | ↑ or normal | Assay anti-insulin Ab | |
| Anti-Tg Ab (TG assay) | ↓ | Assay anti-Tg | Control TG with LC-MS/MS, if available |
| Burosumab therapy (intact FGF23 assay) | ↓ | Patient’s file, therapeutic information | C-terminal FGF23 assay, if available |
| Heterophile Ab, HAAA, RF (all assays) | Mostly ↑ ↓ possible |
Dilution test HBT pretreatment PEG pretreatment RF assay RF adsorbent Adding non-immune Ig Patients’ file: looking for immunotherapy, auto-immune context |
Alternative method needed |
| Gammopathy (all assays) | ↑ ↓ possible |
Dilution test HBT pretreatment PEG pretreatment Protein electrophoresis |
Alternative method needed |
| FDH, thyroid hormone autoantibody (FT4, FT3 assays) | ↑ | Specific assay | Notify in patient’s file, alternative methods needed |
†Interferences are either method-specific or common to all immunoassays (although errors of different magnitudes are recorded among the different methods).
Abbreviations: Ab, antibody; HAAA, human anti-animal antibody; FDH, familial dysalbuminemic hyperthyroxinemia; FGF, fibroblast growth factor; FSH, follicle stimulating hormone; FT4, free thyroxine; FT3, free triiodothyronine; HBT, heterophile blocking tube; LC-MS/MS, liquid chromatography coupled to tandem mass spectrometry; LH, luteotropin hormone; PEG, polyethylene glycol; RF, rheumatoid factor; TSH, thyroid stimulating hormone; Tg, thyroglobulin.