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

• Published in: Clinical chemistry (Baltimore, Md.) Vol. 31; no. 11; pp. 1896 - 1899
• Main Authors: Winter, SD, Kerr, C, McAvoy, M, Gallomore, MD, Smith, C, Lepoff, RB
• Format: Journal Article
• Language: English
• Published: Washington, DC Am Assoc Clin Chem 01.11.1985; American Association for Clinical Chemistry
• Subjects: Analytical biochemistry: general aspects, technics, instrumentation; Analytical, structural and metabolic biochemistry; Autoanalysis - instrumentation; Biological and medical sciences; Blood Chemical Analysis - instrumentation; Chemistry, Clinical - instrumentation; Ethylene Glycol; Ethylene Glycols; Freeze Drying; Fundamental and applied biological sciences. Psychology; Humans; Specimen Handling; Viscosity; Water; Ethylene glycol; Critical study; Freeze drying; Sample preparation; Measurement accuracy; Automatic analyzer
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1093/clinchem/31.11.1896

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.