Validation of a Thiocyanate Method on the Shimadzu UV-1800 Spectrophotometer

Abstract

Abstract Objectives Sodium nitroprusside is used in treatment of hypertensive emergency. In the body, nitroprusside is metabolized to cyanide and cyanide to thiocyanate. Thiocyanate concentration is used to monitor nitroprusside therapy and to evaluate possible exposure to cyanide. A method validation study was performed to assess analytical performance of a new spectrophotometry-based laboratory-developed test for serum thiocyanate. Methods Serum proteins were precipitated using trichloroacetic acid and ferric nitrate. The resulting red-colored solution was measured spectrophotometrically at 450 nm using the Shimadzu UV-1800 spectrophotometer (Shimadzu Scientific Instruments, Columbia, MD). Method precision, linearity, method comparison, and effect of interferences were evaluated according to Clinical Laboratory and Standards Institute guidelines. The Microsoft Excel Analyze-It application was used for statistical analysis. Results Between-run coefficients of variation (CVs) for quality control materials at thiocyanate concentrations of 5 mg/L, 20 mg/L, and 50 mg/L were 9.64%, 6.26%, and 4.25%, respectively. The assay was linear over the analytical measuring range of 5 mg/L to 200 mg/L, with an r2 value of 0.9982. The Deming regression equation for the UV-1601 (comparator) and UV-1800 (new) method was: UV-1800 = 0.998 (95% CI, 0.9762-1.001) UV-1601 + 0.79 (95% CI, –0.1379 to 1.733), and the standard error of the regression was 1.8 mg/L. Interference of <7% was observed in the presence of hemolysis, icterus, and lipemia. Conclusion The analytical performance of the new Shimadzu UV-1800 spectrophotometer method is adequate for measurement of serum thiocyanate in patients on nitroprusside therapy or with cyanide poisoning.