Vertebrate and many invertebrate hemoglobins bind with sulfide to form sulfhemoglobin
. In human hemoglobin A, the binding of sulfide takes place at the heme, but not to the iron, and is effectively irreversible (Berzofsky et al., 1971; Carrico et al., 1978).
Interferences, including lipid-caused turbidity, MetHb, sulfhemoglobin, microcoagulates, putrefaction, and contamination, have called into question the accuracy of COHb measurements obtained by COoximetry.
In addition, forensic chemists should be aware of confounding factors (e.g., methemoglobin, sulfhemoglobin, low hemoglobin, or turbidity) when measuring carboxyhemoglobin in postmortem blood.
CO-oximetry performed on a Radiometer 625 ABL showed a decreased arterial oxyhemoglobin fraction [(F[O.sub.2]Hb).sup.1] of 71.5% (90-95%), a methemoglobin (MetHb) fraction of 1.1% (<2%), an increased carboxyhemoglobin (COHb) fraction of 24.9% (0.5-1.5%), and <1% sulfhemoglobin
(SHb; reference interval, <1%).
All instruments measure oxyhemoglobin ([O.sub.2]Hb), deoxygenated hemoglobin (HHb), carboxyhemoglobin (COHb), and methemoglobin (MetHb); some also signal the presence of or measure sulfhemoglobin
The IL 282 and IL 482 CO-oximeters have not been constructed for determination of sulfhemoglobin
. Nevertheless, these instruments can give a strong indication of the presence of sulfhemoglobin
in a blood sample on the basis of a combined positive result for methemoglobin and a negative value for carboxyhemoglobin.
Sulfhemoglobinemia is the relatively uncommon condition of excess sulfhemoglobin
(SulfHb) in the blood.