Table 1. Baseline Characteristics of Subjects Who Underwent Thyroid Function Tests as Part of the Korea National Health and Nutrition Examination survey (2013 to 2015).
| Characteristic | Total sample | Disease-free populationa | Reference populationb | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Total | Male | Female | Total | Male | Female | Total | Male | Female | |
| No. of subjects | 6,564 | 3,378 (52.8) | 3,186 (47.2) | 6,326 | 3,340 (54.4) | 2,986 (45.6) | 5,574 | 3,060 (56.4) | 2,514 (43.6) |
| Age, yr | 42 (28–56) | 41 (26–54) | 44 (29–58) | 42 (27–55) | 41 (26–54) | 44 (28–57) | 41 (26–55) | 41 (26–54) | 43 (27–57) |
| Age range, yr | |||||||||
| 10–18 | 909 (13.8) | 517 (15.3) | 392 (12.3) | 908 (14.4) | 517 (15.5) | 391 (13.1) | 845 (15.2) | 485 (15.8) | 360 (14.3) |
| 19–29 | 1,106 (16.8) | 566 (16.8) | 540 (16.9) | 1,098 (17.4) | 563 (16.9) | 535 (17.9) | 981 (17.6) | 520 (17.0) | 461 (18.3) |
| 30–39 | 1,084 (16.5) | 556 (16.5) | 528 (16.6) | 1,040 (16.4) | 548 (16.4) | 492 (16.5) | 918 (16.5) | 505 (16.5) | 413 (16.4) |
| 40–49 | 1,101 (16.8) | 569 (16.8) | 532 (16.7) | 1,045 (16.5) | 562 (16.8) | 483 (16.2) | 907 (16.3) | 515 (16.8) | 392 (15.6) |
| 50–59 | 1,196 (18.2) | 584 (17.3) | 612 (19.2) | 1,133 (17.9) | 575 (17.2) | 558 (18.7) | 968 (17.4) | 524 (17.1) | 444 (17.7) |
| 60–69 | 1,058 (16.1) | 527 (15.6) | 531 (16.7) | 997 (15.8) | 518 (15.5) | 479 (16.0) | 860 (15.4) | 460 (15.0) | 400 (15.9) |
| ≥70 | 110 (1.7) | 59 (1.7) | 51 (1.6) | 105 (1.7) | 57 (1.7) | 48 (1.6) | 95 (1.7) | 51 (1.7) | 44 (1.8) |
| Urinary iodine, µg/L | 299.4 (158.9–700.1) | 295.3 (167.1–673.7) | 301.2 (150.8–747.6) | 298.4 (159.1–694.4) | 295.9 (167.3–674.6) | 300.3 (150.4–730.2) | 298.7 (160.1–692.0) | 295.3 (168.8–669.7) | 300.2 (150.8–736.1) |
| Urine iodine/Cr, µg/g | 192.6 (103.2–477.6) | 169.0 (92.2–379.4) | 228.8 (120.0–595.5) | 190.7 (102.2–466.4) | 169.0 (92.2–378.9) | 224.4 (117.7–571.8) | 191.0 (101.6–459.3) | 169.0 (92.3–374.0) | 224.8 (116.6–571.8) |
| TPOAb positivityc | 480 (7.3) | 145 (4.3) | 335 (10.5) | 388 (5.3) | 128 (3.8) | 260 (8.7) | NA | NA | NA |
| History of thyroid | 169 (2.6) | 26 (0.8) | 143 (4.5) | NA | NA | NA | NA | NA | NA |
Values are expressed as number (%) or median (interquartile range).
Cr, creatinine; TPOAb, anti-thyroid peroxidase antibody.
aThe disease-free population was defined as subjects with no prior history of thyroid disease and no history of taking medication that could influence thyroid function; bThe reference population was defined subjects with no prior history of thyroid disease, no history of taking medications that could influence thyroid function, no family history of thyroid disease, negative TPOAb results, and serum free thyroxine levels in the reference range (0.89 to 1.76 ng/dL); cTPOAb positivity was defined as >34.0 IU/mL.