Ferrocyanide ingestion may cause false positives in cyanide determination.
The authors present a patient who ingested a cyanide containing solution and arrived at the hospital without any clinical evidence of intoxication but an elevated blood cyanide level. The authors explain this discrepancy with the following hypotheses: 1) the patient ingested cyanide as an iron-chelated complex; and 2) the sulfuric acid used in the standard microdiffusion technique released cyanide from its iron-bound state to result in the observed elevated blood cyanide. Through a series of in vitro analyses, the authors demonstrate the following: 1) the ingested solution tested positive for cyanide with the sulfuric acid technique and negative for cyanide with acetic acid; 2) the presence of a ferrous salt in the ingested product by a colorimetric redox titration technique; and 3) release of a small fraction of the total cyanide from ferrocyanide by the sulfuric acid technique. The authors conclude: 1) the patient ingested potassium ferrocyanide; and 2) the strong acid used in the cyanide microdiffusion assay will liberate cyanide that is chelated to iron to yield false positive results.
Laforge
M
M
Hôpital Fernand Widal, Paris, France. mlaforge@club-internet.fr
Gourlain
H
H
Fompeydie
D
D
Buneaux
F
F
Borron
S W
SW
Galliot-Guilley
M
M
D000328:Adult; D003124:Colorimetry; D003486:Cyanides / Q000097:blood* / Q000506:poisoning / Q000633:toxicity; D005189:False Positive Reactions; D005290:Ferric Compounds / Q000097:blood; D005295:Ferrocyanides / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D005296:Ferrous Compounds / Q000097:blood; D006801:Humans; D008297:Male
D003486:Cyanides; D005290:Ferric Compounds; D005295:Ferrocyanides; D005296:Ferrous Compounds; C020354:hexacyanoferrate II