title: Thiocyanate in smokers interferes with the Nova magnesium ion-selective electrode.
abstract: Thiocyanate found in serum ordinarily is the metabolite of cyanide that is inhaled with tobacco smoke and ingested with cyanogenic foods. We investigated the effect of the thiocyanate ion (SCN-) on the ionized magnesium (iMg) and ionized calcium (iCa) results determined with the AVL and Nova magnesium and calcium ion-selective electrodes (ISEs). We analyzed saline and pooled serum with added SCN-, and serum from apparently healthy nonsmokers (n = 20) and smokers (n = 20). The mean (and range) of the measured serum SCN- concentration was 0.019 (0.008-0.046) mmol/L for nonsmokers and 0.077 (0.020-0.138) mmol/L for smokers. Only the Nova iMg results decreased with increasing SCN- concentration, and the change was dependent on the baseline iMg concentration. In the absence of Mg, SCN- decreased the voltage response of the Nova Mg ISE to calcium ions. At apparently normal serum iMg and iCa concentrations, the interference by SCN- appeared to be equimolar (iMg = -1.04 x SCN- + 0.52). Thus, the serum SCN- commonly found in smokers causes a significant (P < 0.0001) decrease in the Nova iMg results.
authors.affiliation: Clinical Pathology Department, Warren Grant Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892-1508, USA. nrehak@cc.nih.gov
authors.forename: N N
authors.initials: NN
authors.lastname: Rehak
authors.forename: S A
authors.initials: SA
authors.lastname: Cecco
authors.forename: J E
authors.initials: JE
authors.lastname: Niemela
authors.forename: R J
authors.initials: RJ
authors.lastname: Elin
mesh_terms: D016477:Artifacts; D001322:Autoanalysis / Q000295:instrumentation / Q000379:methods; D002118:Calcium / Q000097:blood*; D004566:Electrodes; D006801:Humans; D008274:Magnesium / Q000097:blood*; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012907:Smoking / Q000097:blood*; D013861:Thiocyanates / Q000097:blood*
chemical_list: D013861:Thiocyanates; D008274:Magnesium; C031760:thiocyanate; D002118:Calcium