The cyanmethemoglobin method measures all hemoglobin pigments EXCEPT which one?

The cyanmethemoglobin method is a laboratory technique primarily used to quantify the concentration of hemoglobin in a blood sample. This method involves converting the various forms of hemoglobin present in the blood to a stable compound known as cyanmethemoglobin, which can then be measured spectrophotometrically.

When considering the different types of pigments related to hemoglobin, sulfhemoglobin is unique in that it cannot be converted to cyanmethemoglobin. It results from the irreversible oxidation of hemoglobin by sulfur compounds, leading to a stable form that does not participate in the cyanmethemoglobin formation that the method relies upon. Consequently, while the cyanmethemoglobin method is effective for measuring various hemoglobin forms like methemoglobin, fetal hemoglobin, and myoglobin, it is not applicable to sulfhemoglobin due to its distinct biochemical characteristics. This is why the correct answer identifies sulfhemoglobin as the pigment not measured by the cyanmethemoglobin method.