Reliability of blood alcohol determinations at clinical chemistry laboratories in Sweden

Known concentrations of ethanol, methanol, isopropanol and its metabolite acetone were added to plasma or whole blood and aliquots of each specimen were sent to clinical chemistry laboratories in Sweden as a declared collaborative study. All participants used gas-liquid chromatography (GC) for quantitative determination of ethanol and other low molecular weight volatiles. The mean within laboratory precision for analysis of ethanol, expressed as coefficient of variation (CV), was 4.7% (range 0-15%). The corresponding between-laboratory CV spanned from 8.0 to 19.4% for 23 control specimens analysed between 1987 and 1992. The mean concentration of ethanol reported was not significantly different from the target value assigned. Between 0 and 3 laboratories reported deviant results (Z-score > 1.96) for each of the control specimens. One laboratory reported the presence of methanol instead of ethanol and three laboratories saw traces of acetone instead of the actual concentration present. One laboratory failed to report that methanol was present and another failed to report the presence of isopropanol. The between-laboratory CV ranged between 9.4 and 30.3% for analysis of methanol in 8 control specimens. The larger variability between laboratories compared with within laboratories probably reflects the different calibration procedures used, such as the preparation and source of the alcohol standards.