yanosis also is observed when nonfunctional hemoglobin such as methemoglobin(正铁血红蛋 白,高铁血红蛋白)or sulfhemoglobin(硫化血红蛋白 ) is present in bloodCyanosis also is observed when nonfunctional hemoglobin such as methemoglobin(正铁血红蛋 白，高铁血红蛋白)or sulfhemoglobin(硫化血红蛋白 ) is present in blood