<prompt> Which among the following is not a cause for cyanosis?MethemoglobinSulfhemoglobinCirrhosisCarboxyhemoglobin  <response>: Cyanosis is caused by reduced hemoglobin. CO poisoning doesnt cause cyanosis. Approximately 5 gdL of unoxygenated hemoglobin in the capillaries generates the dark blue color appreciated clinically as cyanosis. Causes: Central Nervous System: Intracranial hemorrhage, Cerebral anoxia Respiratory System: Pulmonary Hypeension, Pulmonary embolism, Hypoventilation, COPD Cardiac Disorders: Congenital hea disease, Hea failure, Hea valve disease Blood: Methemoglobinemia, Polycythaemia Others: High altitude, Hypothermia, Congenital cyanosis HbM Boston, Obstructive sleep apnea 