Abstract
Lipemia, hemolysis, and icterus commonly interfere with laboratory tests that use optical methods (1). The interference from lipemia is fundamentally different from interferences associated with icterus (bilirubin) and hemolysis (mostly attributable to hemoglobin). In lipemia, chylomicrons and VLDL are suspended particles that scatter light, producing cloudiness or turbidity similar to that seen in milk. Lipemia may interfere in any assay that uses the transmission of light as part of the detection scheme (1). To evaluate the susceptibility of methods to interferences from icterus or hemolysis, it is appropriate to prepare samples with added bilirubin or hemoglobin, respectively (2). By contrast, the lack of readily available, standardized materials to produce lipemic samples complicates the evaluation of lipemia. Glick et al. (2) added IntraLipid, a synthetically produced emulsion for intravenous administration, to serum to simulate lipemic samples. In this issue of Clinical Chemistry , Bornhorst et al. (3) show that samples with added IntraLipid do not perfectly mimic lipemic samples. Thus, native lipemic patient samples have falsely low results for ceruloplasmin, prealbumin, and transferrin measured by immunoturbidimetry, whereas simulated lipemic samples prepared by adding IntraLipid do not. To understand this discrepancy and appreciate its potential occurrence with all light-based methodologies in the clinical laboratory, one must review the features of light scattering pertinent to clinical laboratory instrumentation and the physical chemical differences between naturally lipemic and IntraLipid-supplemented samples. When electromagnetic radiation in the form of light interacts with matter, such as lipid particles, a dipole moment is induced in the particles (4). The magnitude of the dipole moment is proportional to the strength of the electric field and the polarizability of the particles (4). The particles do not need to reflect the light; instead, the phenomenon arises from the difference in the refractive index between the particles (solute) and the solvent …
Published Version
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