A mother and newborn with brown blood

[...]the conformational change renders Hb M-Boston resistant to reduction by methemoglobin reductase (10 ). [...]the conformational change also alters the absorption spectrum of Hb M-Boston relative to both Hb A and methemoglobin A (11 ). Because measurements of oxygen saturation and methemoglobin are based on the absorbance of Hb A at characteristic wavelengths, the presence of a hemoglobin variant with different absorption properties will interfere with these measurements (11 ). [...]the presence of Hb M-Boston also explains the severely underestimated oxygen saturation results and the inability to measure methemoglobin.