{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T10:15:37Z","timestamp":1791281737302,"version":"4.1.0"},"reference-count":36,"publisher":"The Endocrine Society","issue":"6","license":[{"start":{"date-parts":[[2021,2,18]],"date-time":"2021-02-18T00:00:00Z","timestamp":1613606400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2021,5,13]]},"abstract":"<jats:title>Abstract<\/jats:title>\n               <jats:sec>\n                  <jats:title>Context<\/jats:title>\n                  <jats:p>Erythrocytosis is a known side effect of testosterone therapy that can increase the risk of thromboembolic events.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Objectives<\/jats:title>\n                  <jats:p>To study the prevalence and determinants in the development of erythrocytosis in trans men using testosterone.<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Methods<\/jats:title>\n                  <jats:p>A 20-year follow-up study in adult trans men who started testosterone therapy and had monitoring of hematocrit at our center (n\u2005=\u20051073).<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Results<\/jats:title>\n                  <jats:p>Erythrocytosis occurred in 11% (hematocrit\u2005&amp;gt;\u20050.50 L\/L), 3.7% (hematocrit\u2005&amp;gt;\u20050.52 L\/L), and 0.5% (hematocrit\u2005&amp;gt;\u20050.54 L\/L) of trans men. Tobacco use (odds ratio [OR] 2.2; 95% CI, 1.6-3.3), long-acting undecanoate injections (OR 2.9; 95% CI, 1.7-5.0), age at initiation of hormone therapy (OR 5.9; 95% CI, 2.8-12.3), body mass index (BMI) (OR 3.7; 95% CI, 2.2-6.2), and pulmonary conditions associated with erythrocytosis and polycythemia vera (OR 2.5; 95% CI, 1.4-4.4) were associated with hematocrit\u2005&amp;gt;\u20050.50 L\/L. In the first year of testosterone therapy hematocrit increased most: 0.39 L\/L at baseline to 0.45 L\/L after 1 year. Although there was only a slight continuation of this increase in the following 20 years, the probability of developing erythrocytosis still increased (10% after 1 year, 38% after 10 years).<\/jats:p>\n               <\/jats:sec>\n               <jats:sec>\n                  <jats:title>Conclusion<\/jats:title>\n                  <jats:p>Erythrocytosis occurs in trans men using testosterone. The largest increase in hematocrit was seen in the first year, but also after the first years a substantial number of people present with hematocrit\u2005&amp;gt;\u20050.50 L\/L. A reasonable first step in the care for trans men with erythrocytosis while on testosterone is to advise them to quit smoking, to switch to a transdermal administration route, and if BMI is high, to lose weight.<\/jats:p>\n               <\/jats:sec>","DOI":"10.1210\/clinem\/dgab089","type":"journal-article","created":{"date-parts":[[2021,2,18]],"date-time":"2021-02-18T14:09:54Z","timestamp":1613657394000},"page":"1710-1717","source":"Crossref","is-referenced-by-count":86,"title":["Erythrocytosis in a Large Cohort of Trans Men Using Testosterone: A Long-Term Follow-Up Study on Prevalence, Determinants, and Exposure Years"],"prefix":"10.1210","volume":"106","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7122-769X","authenticated-orcid":false,"given":"Milou Cecilia","family":"Madsen","sequence":"first","affiliation":[{"name":"Department of Endocrinology and Center of Expertise on Gender Dysphoria, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, the 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