Clinical prevalence and ramifications of false-positive cardiac troponin I elevations from the Abbott AxSYM Analyzer.
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Biomedical subjects
Gary L Horowitz
Publications and source records attributed to Gary L Horowitz.
Artifactual hyperbilirubinemia due to paraprotein interference.
CONTEXT: Paraprotein interference in automated chemistry is uncommon. We describe 2 patients with paraproteinemia and elevated total bilirubin levels measured erroneously using the Roche total bilirubin assay. OBJECTIVES: To explain the mechanism of this artifactual hyperbilirubinemia and to determine its frequency in patients with monoclonal or increased immunoglobulins. MATERIALS AND METHODS: The assay was performed manually using serum from 2 index patients and from control patients (without M proteins). Total bilirubin was also determined using another manufacturer's assay. A prospective study was then undertaken using serum from 100 consecutive patients with various monoclonal gammopathies and from 13 patients with polyclonal hypergammaglobulinemia and cryoglobulins. For all patients, serum immunoglobulin (Ig) G, IgA, IgM, total and direct bilirubin, creatinine, and a direct spectrophotometric assessment of icterus were measured. RESULTS: After the addition of assay reagents, a white precipitate formed in the reaction mixtures containing serum from the index patients, but not in other samples. This turbidity, rather than the expected color change to pink, increased the absorbance and falsely elevated the total bilirubin value. Serum from both index patients was anicteric, their direct bilirubin measurements were unaffected, and total bilirubin measured using an alternate assay was normal. Among the 113 patients studied, no additional spurious total bilirubin values were detected. CONCLUSION: Paraprotein interference with the Roche automated total bilirubin assay is caused by precipitate formation. This interference is rare and probably idiosyncratic. Spurious hyperbilirubinemia from paraprotein interference may cause clinical confusion. If artifactual elevation of total bilirubin is suspected, the laboratory should examine the specimen for icterus (manually or by spectrophotometry) or measure total bilirubin using a different method.
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Xanthochromia.
CONTEXT: Diagnosis of subarachnoid hemorrhage is usually established by computed tomographic scanning; however, in a few patients, lumbar puncture to examine the cerebrospinal fluid for erythrocytes and xanthochromia is necessary. Some authorities recommend delaying lumbar puncture by 12 hours following onset of symptoms to ensure sufficient time has elapsed for xanthochromia to develop. This recommendation is based on measuring xanthochromia by spectrophotometry. Our hypothesis was that very few hospital laboratories in the United States use this method. OBJECTIVE: To determine the percentage of hospital clinical laboratories that measure for xanthochromia using spectrophotometry. DESIGN, SETTING, AND PARTICIPANTS: Mail survey to 3500 hospital clinical laboratory directors (in collaboration with the College of American Pathologists). Surveys were mailed in January 2001 and the results tabulated 1 month later. Participation was voluntary. MAIN OUTCOME MEASURES: Percentage of hospital clinical laboratories that use spectrophotometry versus visual inspection. RESULTS: Of the 3500 laboratories surveyed, 2551 (72.9%) responded. Of these, 1944 (76.2%) indicated that they evaluated for xanthochromia. Of the 1952 laboratories that answered the question "How do you report your results?" 1947 (99.7%) reported using visual inspection. CONCLUSIONS: When evaluating for xanthochromia in cerebrospinal fluid, nearly all hospital clinical laboratories in the United States use visual inspection. Given this current reality, the recommendation of delaying lumbar puncture by 12 hours needs to be reassessed.
Clinical Laboratory Techniques↗