What does immunoassay interference mean in a drug test?

What does immunoassay interference mean in a drug test?

Substances that alter the measurable concentration of the analyte in the sample or alter antibody binding can potentially result in assay interference. Analytical interference is defined as the effect of a substance present in the sample that alters the correct value of the result.

How would you detect and solve immunoassay interference?

The best way to resolve prozone interference is to dilute the samples and rerun the assay. Elevated endogenous serum components, such as bilirubin (icterus), hemoglobin (hemolysis), lipids (turbidity), and proteins interfere more in homogeneous than heterogeneous assays.

What happens in a competitive immunoassay?

In a competitive immunoassay, the sample analyte is mixed with labelled analyte, which both compete for a limited number of antibody-binding sites. Hence, the signal produced by the bound labeled analyte is usually inversely proportional to the amount of sample analyte.

What is a competitive assay?

A competitive binding assay typically measures the binding of a labeled ligand to a target protein in the presence of a second, competing but unlabeled ligand. This assay can be used to assess qualitative binding information as well as relative affinities of two or more molecules for one target.

Can muscle relaxers cause false positive drug test?

Several other substances also cause false-positive tricyclic antidepressant toxic screen results, including certain antipsychotic medications, antihistamines, and the muscle relaxant cyclobenzaprine.

What are the key advantage of immunoassay?

Immunoassays have become increasingly popular tools for measuring biologic analytes, because they offer sensitive, specific results and are relatively easy to use. In addition, some immunoassay methods are rapid, yield improved precision, and are relatively easy to automate, thus requiring less hands-on involvement.

Why is interference a problem with competitive immunoassay?

Interferences of drug metabolite with assay intended for parent drug is a common problem. Therefore results obtained by immunoassays must be carefully interpreted with clinical condition of patients and if discrepancy observed between an analyte values measured by an immunoassay with clinical picture, issues of interference must be considered.

What is bidirectional interference in an immunoassay?

Bidirectional interference—positive with certain analyte and interferent concentrations, and negative with other concentrations—has been observed in some immunoassays. Use of monoclonal antibodies in modern immunoassays has improved assay specificity, reducing cross reactivity.

What is percentage of interference in immunoassay assays?

Approximately 40% of serum samples contain non-analyte antibody binding substances, with 15% interference in non-blocked assays. 79,100 Ward et al. identified 7 out of 21,000 samples from a hospital population with heterophile interference and HAMA, the interference being as low as 0.03% in blocked IMAs.

Why are competitive immunoassays less often used in clinical practice?

Competitive immunoassays are less often affected, although they may show falsely high values if the interfering antibody outcompetes the assay antibody for tracer, or falsely low values if they bind preferentially to the analyte over the tracer. William Clarke, Alex J. Rai, in Contemporary Practice in Clinical Chemistry (Fourth Edition), 2020