A NEW BIOLOGICAL ASSAY FOR MEASURING CYANIDE IN BLOOD

Clinical diagnosis of cyanide poisoning is complicated by the lack of an easy, convenient assay for cyanide concentration in blood. Therapy may be delayed with unconfirmed diagnosis because the conventional ant idote to cyanide poisoning exposes patients to substantial risks. We d eveloped a new spectrophotometric assay to measure cyanide by extracti on into a sodium hydroxide trap, followed by the addition of exogenous methemoglobin as a colormetric indicator. Samples of blood from 15 he althy subjects and 5 patients who had received prolonged nitroprusside infusions were assayed. To optimize assay characteristics, methemoglo bin concentrations, pH, temperature, incubation time, and buffer stren gths were varied. Duplicate samples were assayed by using the polarogr aphic method for assay validation. Over a range from 300 ng/mL to 7 mu g/mL, the correlation between methods was r = 0.983. Interassay and i ntraassay variability were 5% and 2%, respectively. Samples drawn from the five patients and tested by using both methods yielded a correlat ion of r = 0.978. This new assay for cyanide in blood may greatly faci litate the diagnosis and treatment of cyanide ingestion. The use of me themoglobin as the colorimetric indicator in the assay contributes to its low cost and ease of use. Implications: Cyanide, an important fact or in death from burn-related inhalation injury, is difficult and time -consuming to measure. We developed a new, rapid blood test for cyanid e using methemoglobin as a colormetric indicator. A rapid, accessible test for cyanide may speed the diagnosis and treatment of cyanide pois oning.