Clinical Chemistry
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Clinical Chemistry 31: 1896-1899, 1985;
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Clinical Chemistry, Vol 31, 1896-1899, Copyright © 1985 by American Association for Clinical Chemistry

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

SD Winter, C Kerr, M McAvoy, MD Gallomore, C Smith and RB Lepoff

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.




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Copyright © 1985 by the American Association for Clinical Chemistry.