In a recent issue of Nefrologia, we read the paper of Dr Vega and colleagues entitled “Study on overhydration in dialysis patients and its association with inflammation”.1 We thank for their valuable research evaluating hydration status and body composition in patients on haemodialysis and its relation to inflammation. They found an association between hydration status and low prealbumin (transthyretin) levels. We want to make some comments on transthyretin (TTR) which was assessed in their study.

Serum TTR has been reported to be a reliable outcome predictor in patients with kidney disease.2 Previous studies suggested that several factors can affect serum TTR levels. Disorders such as anorexia nervosa, bulimia nervosa, rheumatoid arthritis, ankylosing spondylitis, major depression, trauma, malignancy, protein losing enteropathy, Kawasaki disease, liver diseases, Helicobacter pylori infection and thyroid diseases were shown to alter serum TTR levels.3,4 Vega et al. did not mention these contributing diseases in their paper.

Several drugs such as anabolic steroids, corticosteroids, progestational agents, estrogens, antithyroid drugs and nonsteroidal antinflammatory drugs can alter serum TTR levels.5,6 Also, dietary supplements such as vitamin A, vitamin C, zinc and omega-3 fatty acids can alter these levels.7,8 In this respect, the authors should define whether the participants use any of these drugs and dietary supplements. In addition, alcohol usage is another confounder that should be described whether the participants use.9

Lastly, we think that body position is essential to state while taking blood specimen. It is recommended that blood specimens for measuring plasma proteins be taken after nearly 15–20min in the sitting position.5 Otherwise, concentrations should be evaluated with consideration of position. Lower levels are to be expected in bedridden patients.5 Therefore, interpretation of results with its current form seems problematic.

Mears and many researchers suggested that serum TTR concentration was not affected by hydration status.10 In this respect, authors’ claim as association between hydration status and low TTR levels seems suspicious irrespective of taking into account above contributing factors. Clarifying these concerns will provide clearer picture to the readers.