title: Plasma Levels of Free Thyroxine and Risk of Major Bleeding in Bariatric Surgery.
abstract: BACKGROUND
  In a recent study of patients using vitamin K antagonists, those with low free thyroxin (FT4) levels within the normal range had a 3- to 5-fold increased risk of major bleeding. We tested the hypothesis that low levels of preoperative FT4 within the reference range are associated with an increased risk of major bleeding during and after bariatric surgery.
  
  
  METHODS
  The charts of 2,872 consecutive patients undergoing bariatric surgery were retrospectively screened for bleeding episodes. Patients with major bleeding until 1 month after surgery were compared to randomly selected control patients without bleeding, in a ratio of 1:4. We evaluated the association between preoperative FT4 levels and the risk of major bleeding by logistic regression.
  
  
  RESULTS
  Seventy-two cases (2.5%) with major bleeding were identified and 288 controls were selected. The median plasma level of FT4 was 13 pmol/l (interquartile range: 12-14) in the cases as well as in the controls. No clear effect was observed of low levels of FT4 on the risk of major bleeding: odds ratio 1.48 (95% CI: 0.46-4.80) for patients with an FT4 level <11 pmol/l, 1.03 (0.49-2.18) for patients with an FT4 level <12 pmol/l, and 1.12 (0.65-1.94) for patients with an FT4 level <13 pmol/l as compared to patients with FT4 values greater than or equal to these cutoff levels.
  
  
  CONCLUSIONS
  We did not observe an increased risk of major bleeding with low levels of FT4 in patients undergoing bariatric surgery.
authors: Department of Internal Medicine, Medical Center Slotervaart, University of Amsterdam, Leiden, The Netherlands; Departments of, Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, Leiden, The Netherlands.
authors: Laura P B
authors: LP
authors: Elbers
authors: Department of Internal Medicine, Medical Center Slotervaart, University of Amsterdam, Leiden, The Netherlands.
authors: Hjalmar A
authors: HA
authors: Boon
authors: Department of Internal Medicine, Medical Center Slotervaart, University of Amsterdam, Leiden, The Netherlands.
authors: Maaike I
authors: MI
authors: Moes
authors: Department of Internal Medicine, Medical Center Slotervaart, University of Amsterdam, Leiden, The Netherlands; Departments of, Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, Leiden, The Netherlands.
authors: Bregje
authors: B
authors: van Zaane
authors: Department of Internal Medicine, Medical Center Slotervaart, University of Amsterdam, Leiden, The Netherlands; Departments of, Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, Leiden, The Netherlands.
authors: Dees P M
authors: DP
authors: Brandjes
authors: Departments of, Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, Amsterdam, Leiden, The Netherlands.
authors: Eric
authors: E
authors: Fliers
authors: Departments of, Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, Leiden, The Netherlands.
authors: Harry R
authors: HR
authors: Büller
authors: Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands; Einthoven Laboratory for Vascular Medicine, Leiden University Medical Center, Leiden, The Netherlands.
authors: Suzanne
authors: S
authors: Cannegieter
authors: Department of Internal Medicine, Medical Center Slotervaart, University of Amsterdam, Leiden, The Netherlands; Departments of, Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, Leiden, The Netherlands.
authors: Victor E A
authors: VE
authors: Gerdes
keywords: Obesity; Surgery; Thyroid function; Thyroid hormone; Thyroid tests; Thyroxine