Several influences modulate biochemical responses to a weight-adjusted @entity1955 ( @entity2016 ) replacement dose. We conducted a secondary analysis of the relationship of @entity2016 dose to TSH and free T3 (FT3), using a prospective observational study examining the interacting equilibria between thyroid parameters. We studied 353 @entity1 on steady-state @entity2016 replacement for @entity1669 or after surgery for malignant or benign @entity1374 . Peripheral deiodinase activity was calculated as a measure of T4-T3 conversion efficiency. In euthyroid subjects, the median @entity2016 dose was 1.3 g/kg per day (interquartile range (IQR) 0.94,1.60). The dose was independently associated with gender, age, aetiology and deiodinase activity (all P<0.001). Comparable FT3 levels required higher @entity2016 doses in the @entity189 group (n=143), even after adjusting for different TSH levels. Euthyroid @entity259 @entity1 (n=50) received 1.57 g/kg per day @entity2016 (IQR 1.40, 1.69), compared to 1.19 g/kg per day (0.85,1.47) in @entity1669 (P<0.01, n=76) and 1.08 g/kg per day (0.82, 1.44) in @entity1 operated on for benign disease (P< 0.01, n=80). Stratifying @entity1 by deiodinase activity categories of <23, 23-29 and >29nmol/s revealed an increasing FT3-FT4 dissociation; the poorest converters showed the lowest FT3 levels in spite of the highest dose and circulating FT4 (P<0.001). An @entity2016 -related FT3-TSH disjoint was also apparent; some @entity1 with fully suppressed TSH failed to raise FT3 above the median level. These findings imply that @entity6145 conversion efficiency is an important modulator of the biochemical response to @entity2016 ; FT3 measurement may be an additional treatment target; and @entity2016 dose escalation may have limited success to raise FT3 appropriately in some cases.

Variation in the biochemical response to XXXX therapy and relationship with peripheral @entity6145 conversion efficiency.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity1669 :: ('MESH:D013967', 'Disease') :: ['autoimmune thyroiditis'] @entity1955 :: ('MESH:D013974', 'Chemical') :: ['levothyroxine'] @entity2016 :: ('CHEBI:18332', 'Chemical') :: ['l-T4'] @entity189 :: ('MESH:D002277', 'Disease') :: ['carcinoma'] @entity6145 :: ('CHEBI:60311', 'Chemical') :: ['thyroid hormone'] @entity259 :: ('MESH:D013964', 'Disease') :: ['athyreotic thyroid carcinoma'] @entity1374 :: ('MESH:D013959', 'Disease') :: ['thyroid disease']
@entity1955 :: (MESH:D013974,Chemical) :: ['l-thyroxine']
