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PubMed · 7955368

Interference with clinical laboratory analyses.

Abstract

Interference by endogenous and exogenous substances with assays for clinical analytes is a common problem in laboratory medicine. For this review, we defined interference as "the effect of a substance present in the sample that alters the correct value of the result, usually expressed as concentration or activity, for an analyte." There are four major endogenous compounds that consistently interfere with laboratory results: hemoglobin, bilirubin, lipids, and paraproteins. The major exogenous sources of interference are drugs prescribed for the patient; and there are several excellent compendia of the effect of drugs on clinical laboratory tests. We recommend determining whether the interference is dependent or independent of the analyte for the assay. Further, we propose an approach to the identification and resolution of an interference problem for the clinical laboratory and make recommendations to manufacturers.

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BibTeXRIS

M H Kroll, R J Elin. 1994. Interference with clinical laboratory analyses.. https://pubmed.ncbi.nlm.nih.gov/7955368/

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Solvent partition of 14C-unconjugated bilirubin to remove labeled polar contaminants.

Polar derivatives contaminating unconjugated bilirubin (UCB) are customarily extracted with weak alkali. As UCB degrades rapidly at alkaline pH, regeneration of polar derivatives may limit purification. This problem is especially important when trying to eliminate radiolabeled contaminants from 14C-UCB. As polar derivatives of UCB should have a much greater aqueous to CHCl3 partition ratio (PR) than UCB even at neutral pH, where degradation of UCB is minimal, 14C-UCB in CHCl3 was serially extracted with an aqueous buffer at pH 7.0 to determine whether labeled derivatives could be preferentially removed. A single extraction of customarily purified 14C-UCB removed 0.18+/-0.06% of the radioactivity as labeled derivatives. Subsequent serial extractions yielded a stable, 67% lower 14C-PR with only 0.03% of radioactivity as labeled derivatives. Reverse-phase high-performance liquid chromatography (HPLC) of phases from later extractions revealed, however, that up to 1.1% of the disintegration per minute (dpm) in CHCl3 phases and up to 50% in aqueous phases were polar impurities. HPLC of partition phases spiked with purified 14C-UCB revealed that these impurities derived from incomplete extraction of the least polar impurities and their regeneration during HPLC. In the dark under argon, 14C-UCB in CHCl3or dimethyl sulfoxide (DMSO) solution degraded very slowly to polar derivatives. Extraction of impurities from a solution of 14C-UCB in CHCl3 is best done using pH 7.0 buffer, with removal of over 80% of the labeled contaminants remaining after customary purification by alkaline extraction.

Bilirubin↗