Analytic evaluation and application of a novel spectrophotometric serum lithium method to a rapid response laboratory

The authors present an evaluation of the Lithium DST spectrophotometric method developed by Thermotrace (Victoria, Australia) on a Hitachi 917 analyzer. Accuracy was assessed by method comparison with an ion-selective electrode (ISE; Roche Integra 700) (n = 80). Linearity, within-run and between-run precision, and susceptibility to interference by hemolysis, icterus, lipemia, and sodium were assessed. The method was linear to 3.0 mM/L, and analyzer auto-dilution extended the reportable range to 7.2 mmol/L. Within-run coefficient of variation was 1.5% at 0.68 mmol/L and 0.7% at 2.06 mM/L. Between-run precision for the same lithium concentrations assayed daily for 20 days were 3.1% and 1.9%, respectively. Method agreement with ISE was excellent, with an intercept of 0.000 and slope of 1.000 by Passing Bablock regression analysis. Hemolysis, icterus, lipemia, and high and low sodium levels did not significantly interfere. The manufacturer's recommended calibration stability of 1 week was confirmed. The authors conclude that this method is reliable, accurate, and precise. The Thermotrace serum lithium spectrophotometric method provides a useful alternative to ISE or flame photometry, facilitates workstation consolidation on the Hitachi 917 multiple-channel analyzer, and is well adapted for use in a rapid response laboratory.