Effect of Hemolysis, High Bilirubin, Lipemia, Paraproteins, and System Factors on Therapeutic Drug Monitoring
Among the endogenous interferents affecting assay results, the most common are bilirubin, hemoglobin, lipids, and paraproteins. These interferents may affect therapeutic drug monitoring (TDM), drugs of abuse (DAU) testing, and toxicology assays of any format where the sample is used directly for analysis without any pretreatment of specimen. Immunoassays are commonly used in clinical laboratories where analyte-specific antibody or binding agents are used to estimate the analyte concentration in the specimen. Some enzyme and chemistry assays are also utilized in TDM and DAU analysis. Such assays use various types of signals, the most common being colorimetry, fluorimetry, and chemiluminescence. Assays may be prone to interference depending on the format or label used. Commercial assay kits report the result of such interference in the kit inserts (up to levels of >20 mg/dL bilirubin, >500 mg/dL hemoglobin, and >1000 mg/dL lipids). The interference is caused by the optical, fluorescent, or chemiluminescent properties of these interferents. Thus, bilirubin interferes by its absorption and fluorescence properties, hemoglobin by its absorption, fluorescence and chemiluminescence properties, and lipids interfere mostly from their light-scattering (turbidity) properties. Bilirubin and hemoglobin may also interfere because of side reactions in the assay. Modern auto-analyzers can detect all three interferents and flag the results. Flagged results should be carefully reviewed for the accuracy. Both hypo- and hyper-proteinemia can affect assay results. Paraproteins interfere in many assays by precipitating out during the sample blanking step thus producing false results. Another source of interference may be from probe (sample or reagents) or reaction cuvettes carryover contamination in random-access auto-analyzers. If the validity of test results is questioned, the assay should be repeated either by removing the interferent from the sample or by using different method which is known to suffer less from that type of interference.
KeywordsBilirubin hemoglobin lipids interference assays
Unable to display preview. Download preview PDF.
- 1.Fonseca-Wolheim FD. Hemoglobin interference in the bichromatic spectrophotometry of NAD(P)H at 340/380 nm. Eur J Clin Chem Clin Biochem 1993;31:595–601.Google Scholar
- 2.NCCLS Recommendation (EP7-P), Interference testing in Clinical Chemistry, 1986 (Vol. 6, No. 13), pp 259–371.Google Scholar
- 3.Miller JM, Valdes R Jr. Methods for calculating crossreactivity in immunoassays. J Clin Immunoassay 1992;15:97–101.Google Scholar
- 5.Tietz NW. Clinical Guide to Laboratory Tests. 3rd Ed. Philadelphia, PA: WB Saunders Company; 1995:88–91.Google Scholar
- 6.Perlstein MT, Thibert RJ, Watkins RJ, Zak B. Spectrophotometric study of bilirubin and hemoglobin interactions in several hydrogen peroxide generating procedures. Clin Chem 1977;23:1133 [Abstract].Google Scholar
- 10.Sonntag O, Glick MR. Serum-index und interferogram-ein neuer weg zur prufung und darstellung von interferengen durch serumchromogene. Lab Med 1989;13:77–82.Google Scholar
- 16.Park Y, Grellner, Harris WS, Miles JM. A new method for the study of chylomicron kinetics in vivo. Am J Physiol Endocinol Metab 2000;279:E1258–263.Google Scholar
- 20.Laurell CB, Waldenstrom J. Sera with exceptional appearance and the euglobulin reaction as screen test. Acta Med Scand Suppl 1961;367:97–100.Google Scholar
- 23.Viljoen A, Cockrill G, Martin SC. The ability of the lipemic index to predict assay interference. Clin Chem 2006:52: A8 [Abstract].Google Scholar
- 24.ADVIA 1650 IgA, IgG, and IgM Method Sheets.Google Scholar