Link to Methaemoglobin
Link to Methaemoglobinaemia Teaching Material
Link to Problems for discussion
Methaemoglobinaemia
Methaemoglobin is occasionally produced therapeutically and is probably seen more commonly from recreational amyl nitrate use. There is a wide range of drugs and chemicals that can cause the oxidative stress that transforms Fe2+ to Fe3+ causing the patient to appear cyanosed, altering the oxygen carrying capacity and turning blood to a chocolate-brown colour.
See Bob Hoffmans talk [822 KB] on treatment of MetHb in G6PD deficiency
See Paediatric Case report [413 KB] from Jonathon Mervis, Cape Town
BEDSIDE MEASUREMENT OF METHAEMOGLOBIN
Traditonally best side tests have been based on the detection of chocolate brown blood on tissue paper such as this example of a patient with propanil poisoning.
A refinement and validation of this observation using a color chart has been published: Shihana F, et al. A simple quantitative bedside test to determine methemoglobin. Ann Emerg Med 2010 Feb;55(2):184-9 PMID19818531 Fulltext
The colour chart instructions and the data for constructing it can be downloaded here [93 KB]
A computer generated chart for printing can be downloaded here [121 KB]
