"Carryback": effect of viscous liquid controls on the preceding sample analyzed with the SMA II continuous-flow analyzer

"Carryback": effect of viscous liquid controls on the preceding sample analyzed with the SMA II continuous-flow analyzer

We systematically studied the "carryback" effect of ethylene glycol-based controls on the preceding sample on an SMA II continuous-flow analyzer. Including Beckman Level 1 unassayed liquid control material as a sample lowered the 12 analyte values of the preceding sample by an average of 2...

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Bibliographic Details
Published in:Clinical chemistry (Baltimore, Md.) Vol. 31; no. 11; p. 1896
Main Authors: Winter, S D, Kerr, C, McAvoy, M, Gallomore, M D, Smith, C, Lepoff, R B
Format: Journal Article
Language:English
Published: England 01-11-1985
Subjects:
Autoanalysis - instrumentation
Blood Chemical Analysis - instrumentation
Chemistry, Clinical - instrumentation
Ethylene Glycol
Ethylene Glycols
Freeze Drying
Humans
Specimen Handling
Viscosity
Water
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Summary:We systematically studied the "carryback" effect of ethylene glycol-based controls on the preceding sample on an SMA II continuous-flow analyzer. Including Beckman Level 1 unassayed liquid control material as a sample lowered the 12 analyte values of the preceding sample by an average of 2.7%, Level 2 (the most viscous) by an average of 4.4%, and Level 3 by 3.2%. Water-reconstituted lyophilized control material caused no carryback effect, but lyophilized control reconstituted with 330 mL/L ethylene glycol decreased the preceding sample's results by 4.1% (average carryback). We believe that carryback is caused by the drag placed on the sample line by a viscous sample, which decreases the volume of the preceding sample that is delivered to the reagent or pre-dilution mixing coils. Our findings were confirmed on another SMA II. Limited study of a SMAC analyzer gave inconclusive results, but further evaluation of continuous-flow systems for carryback is warranted. Carryback substantially increases total analytical variability.
ISSN:0009-9147
DOI:10.1093/clinchem/31.11.1896