Endocrinol Metab.  2020 Mar;35(1):106-114. 10.3803/EnM.2020.35.1.106.

Association between Serum Free Thyroxine and Anemia in Euthyroid Adults: A Nationwide Study

• Kim M
• Kim BH
• Lee H
• Jang MH
• Kim JM
• Kim EH
• Jeon YK
• Kim SS
• Kim IJ

• KMID: 2471726
• DOI: http://doi.org/10.3803/EnM.2020.35.1.106

Abstract

BACKGROUND
Studies on the relationship between thyroid function and anemia in the euthyroid range are scarce. We aimed to evaluate the association between anemia and serum free thyroxine (fT4) and thyrotropin (TSH) in euthyroid adults.
METHODS
Data on 5,352 participants aged ≥19 years were obtained from the Korea National Health and Nutrition Examination Survey VI (2013 to 2015). Anemia was defined as hemoglobin (Hb) <13 and <12 g/dL for men and women, respectively.
RESULTS
Overall, 6.1% of participants had anemia, and more women (9.9%) had anemia than men (2.8%, P<0.001). In multivariate analysis, serum fT4 levels, but not TSH, were positively associated with serum Hb levels in both sexes (P<0.001, each). Serum Hb levels linearly reduced across decreasing serum fT4 quartile groups in both sexes (P<0.001, each). After adjusting for potential confounding factors, participants with low-normal fT4 had 4.4 (P=0.003) and 2.8 times (P<0.001) higher risk for anemia than those with high-normal fT4 among men and women, respectively. When participants were divided into two groups at 50 years of age, in younger participants, men and women with the first quartile were at higher risk of anemia than men with the second quartile (odds ratio [OR], 3.3; P=0.029) and women with the forth quartile (OR, 3.2; P<0.001), respectively. This association was not observed in older participants.
CONCLUSION
These results suggest that a low-normal level of serum fT4 was associated with a lower serum Hb level and a higher risk of anemia in euthyroid adults, especially in younger participants.

Keyword

Thyroid function tests; Thyrotropin; Thyroxine; Anemia; Hemoglobins

MeSH Terms

Adult*
Anemia*
Female
Humans
Korea
Male
Multivariate Analysis
Nutrition Surveys
Thyroid Function Tests
Thyroid Gland
Thyrotropin
Thyroxine*
Thyrotropin
Thyroxine

Figure

• 

  Fig. 1 Serum hemoglobin (Hb) levels according to serum free thyroxine (T4) quartiles in (A) euthyroid men and (B) women. Values are presented as the estimated mean with standard error of the means.

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