AN EVALUATION OF THE EKTACHEM SERUM LITHIUM METHOD AND COMPARISON WITH FLAME EMISSION-SPECTROMETRY

We evaluated the performance of a new colorimetric method in dry chemi stry for serum lithium (Li) assay using an Ektachem E500 analyser. Imp recision results were acceptable and the linearity was verified for co ncentrations within the range of 0.2-3.9 mmol l(-1), i.e. y(measured)= 1.02x(calculated)+0.07, r=0.99. The Ektachem Li assay was unaffected b y potassium (K), calcium (Ca) and magnesium (Mg) at all concentrations tested. Significant interference was caused by sodium (Na) and haemog lobin. Statistically and clinically significant interference was cause d by high concentrations of Na (213 mmol l(-1)) with a bias of 0.20 mm ol l(-1) (p=0.02) and by high levels of haemoglobin (280 mu mol l(-1)) with a bias of 0.20 mmol l(-1) (p=0.01). Comparison of serum Li resul ts from 80 patient samples assayed using the Ektachem method with thos e obtained using the IL943, a flame atomic emission spectrometry (FAES )-based method, gave a regression line equation: y(Ektachem)=0.95X(FAE S)+0.13, r=0.96. The data revealed a mean difference of 0.10 mmol l(-1 ) between the Ektachem and FAES results that was statistically signifi cant (p=0.01), but clinically negligible. We conclude that the Kodak m ethod provides reliable Li serum results and represents a valid altern ative to the FAES method.