Lancet
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Antineutrophil cytoplasmic antibody (c-ANCA) has a reported sensitivity and specificity greater than 90% for active Wegener's granulomatosis in selected patients with previously-defined disease. Because of these reports, some clinicians believe that a positive c-ANCA result provides strong circumstantial evidence for the diagnosis of Wegener's granulomatosis in patients with compatible clinical symptoms. However, this approach has not been examined prospectively. ⋯ The specificity remained greater than 90% regardless of baseline corticosteroid use or disease activity; however, the sensitivity and positive predictive value remained poor. For Wegener's granulomatosis defined by biopsy criteria and compatible clinical symptoms, the sensitivity was 83% (53%-100%); however, the positive predictive value was 36%. These results raise serious questions about the use of positive c-ANCA tests in diagnosing Wegener's granulomatosis in patients with clinical symptoms alone.
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Hydroxocobalamin combines with cyanide to form cyanocobalamin. We hypothesised that the amount of cyanocobalamin formed after a fixed dose of hydroxocobalamin given for cyanide poisoning would correlate with initial blood cyanide concentration. We determined blood cyanide concentration in 12 patients exposed to residential fires, and compared this with markers of the amount of cyanocobalamin formed after treatment with 5 g intravenous hydroxocobalamin. ⋯ In one patient with initial blood cyanide concentration of 96 mumol/L, however, plasma cyanocobalamin concentration approximately doubled after a second 5 g dose of hydroxocobalamin. 5 g of hydroxocobalamin appears capable of binding all available cyanide ions for blood cyanide concentrations up to about 40 mumol/L. Beyond this, more hydroxocobalamin must be given for remaining cyanide ions to be bound. This information will allow clinicians to use rapidly measurable plasma cyanocobalamin concentrations to gauge severity of exposure and evaluate adequacy of treatment.