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In view of the past diagnosis of pulmonary arteriovenous fistulae made at 4 years of age, a repeat cardiac catheterisation study was done, which revealed no shunt at any level. Interestingly, arterial oxygen tension of the chocolate-brown blood was normal in all the samples, suggesting the possibility of methaemoglobinaemia. Co-oximetry revealed methaemoglobin levels of 36%, confirming the diagnosis. Secondary causes were ruled out. The family was counselled about the hereditary nature of the condition.<\/jats:p>","DOI":"10.1136\/bcr-2018-228470","type":"journal-article","created":{"date-parts":[[2019,4,2]],"date-time":"2019-04-02T05:15:26Z","timestamp":1554182126000},"page":"e228470","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":3,"title":["Congenital methaemoglobinaemia diagnosed in an adolescent boy"],"prefix":"10.1136","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9247-0709","authenticated-orcid":false,"given":"Amal","family":"Paul","sequence":"first","affiliation":[{"name":"Cardiology, Christian Medical College and Hospital Vellore, Vellore, Tamil Nadu, India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Sujith Thomas","family":"Chacko","sequence":"additional","affiliation":[{"name":"Cardiology, Christian Medical College and Hospital Vellore, Vellore, Tamil Nadu, India"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"239","published-online":{"date-parts":[[2019,3,31]]},"reference":[{"key":"2025082723135323000_12.3.e228470.1","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1182\/asheducation-2005.1.19","article-title":"Gregg XT - Red cell enzymes","volume":"2005","author":"Prchal","year":"2005","journal-title":"Hematology"},{"key":"2025082723135323000_12.3.e228470.2","doi-asserted-by":"crossref","first-page":"1408","DOI":"10.1182\/blood.V75.7.1408.1408","article-title":"Serine-proline replacement at residue 127 of NADH-cytochrome b5 reductase causes hereditary methemoglobinemia, generalized type","volume":"75","author":"Kobayashi","year":"1990","journal-title":"Blood"},{"key":"2025082723135323000_12.3.e228470.3","doi-asserted-by":"publisher","DOI":"10.1542\/peds.112.2.e158"},{"key":"2025082723135323000_12.3.e228470.4","doi-asserted-by":"publisher","DOI":"10.1097\/00000542-198901000-00021"},{"key":"2025082723135323000_12.3.e228470.5","doi-asserted-by":"publisher","DOI":"10.1373\/clinchem.2004.035154"},{"key":"2025082723135323000_12.3.e228470.6","doi-asserted-by":"publisher","DOI":"10.1213\/ANE.0b013e3181c91bb6"},{"key":"2025082723135323000_12.3.e228470.7","doi-asserted-by":"publisher","DOI":"10.1093\/brain\/awm337"},{"key":"2025082723135323000_12.3.e228470.8","doi-asserted-by":"crossref","first-page":"665","DOI":"10.1007\/BF03016550","article-title":"Perioperative methemoglobinemia","volume":"52","author":"Johnson","year":"2005","journal-title":"Can J Anaesth"},{"key":"2025082723135323000_12.3.e228470.9","doi-asserted-by":"crossref","first-page":"240","DOI":"10.1097\/MJT.0000000000000028","article-title":"Ascorbic acid for the treatment of methemoglobinemia: the experience of a large tertiary care pediatric hospital","volume":"21","author":"Rino","year":"2014","journal-title":"Am J Ther"},{"key":"2025082723135323000_12.3.e228470.10","doi-asserted-by":"publisher","DOI":"10.1016\/S0196-0644(99)70167-8"}],"container-title":["BMJ Case Reports"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/syndication.highwire.org\/content\/doi\/10.1136\/bcr-2018-228470","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,8,28]],"date-time":"2025-08-28T06:14:03Z","timestamp":1756361643000},"score":1,"resource":{"primary":{"URL":"https:\/\/casereports.bmj.com\/lookup\/doi\/10.1136\/bcr-2018-228470"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,3]]},"references-count":10,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2019,3,31]]},"published-print":{"date-parts":[[2019,3]]}},"alternative-id":["10.1136\/bcr-2018-228470"],"URL":"https:\/\/doi.org\/10.1136\/bcr-2018-228470","relation":{},"ISSN":["1757-790X"],"issn-type":[{"value":"1757-790X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,3]]}}}