[Acquired methemoglobinemia--case report].

Methemoglobinemia; an increased concentration of methemoglobin in the blood, is an altered state of hemoglobin whereby the ferrous form of iron is oxidized to the ferric state, rendering the heme moiety incapable of carrying oxygen. The authors present a case of 49-year-old man who was admitted to the department of chest medicine with dyspnea, weakness and cyanosis in whom differential diagnosis excluded acute and chronic pulmonary and cardiovascular disease. Clinical cyanosis and low measured oxygen saturation in the presence of normal arterial oxygen tension was highly suggestive of methemoglobinemia ("saturation gap"). Methemoglobin level, measured at the acute phase of disease was elevated at 16%. Episode resolved spontaneously. Causes of methemoglobinemia was not established.