A 49-year-old male was admitted following a house fire that resulted in burns to 20 % of his total body surface area. Empiric hydroxocobalamin was given for presumed cyanide poisoning secondary to smoke inhalation. Plasma and urine from the patient were noted to have an intense dark red/purple hue (Fig. 1).

Figure 1.
figure 1

Wine-colored urine ( left ) and plasma ( right ) from hydroxocobalamin treatment for cyanide poisoning.

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Approximately 35 % of fire victims experience toxicity from cyanide, generated during pyrolysis of such synthetic materials as plastics, rugs, silks, and furniture.1 Cyanide inhibits cytochrome oxidase in the electron transport chain and blocks aerobic metabolism, causing a histotoxic hypoxia. Hydroxocobalamin chelates cyanide and forms the nontoxic, renally excreted cyanocobalamin. A common side effect of hydroxocobalamin is a stunning dark red/purple discoloration of the recipient’s skin, mucosal membranes, and body fluids, including plasma and urine. Although the pigmentation is harmless and resolves spontaneously within days, it can cause analytical interference with a number of common chemistry, hematology, and coagulation tests.2 The clinical significance of these transient alterations remains to be determined. More concerning is the increase in carboxyhemoglobin and methemoglobin and decrease in oxyhemoglobin from hydroxocobalamin interference observed with certain co-oximeters.3 As smoke inhalation victims often demonstrate concomitant carbon monoxide and cyanide toxicities, initial blood gas measurements should be obtained prior to hydroxocobalamin administration. Our patient had a carboxyhemoglobin level of 20.5 % (normal, < 2.5 %) before hydroxocobalamin treatment, thereby confirming concurrent carbon monoxide poisoning.