Table 1.
Baseline Characteristics of Patients Treated vs Not Treated With LT4
| LT4 Treatment | ||||
| Characteristics | Yes (n = 1214) | No (n = 6776) | Total (N = 7990) | P |
| Age, y | 0.09 | |||
| Mean, SD | 31.9 (4.7) | 31.5 (5.1) | 31.6 (5.1) | |
| TSH concentration, mIU/L | 0.001 | |||
| Mean, SD | 4.7 (1.6) | 3.3 (0.9) | 3.5 (1.1) | |
| TSH concentration group, mIU/L | <0.001 | |||
| 2.5 –4.0 | 473 (39.0%) | 5734 (84.6%) | 6207 (77.7%) | |
| 4.1 –10.0 | 741 (61.0%) | 1042 (15.4%) | 1783 (22.3%) | |
| Race/Ethnicity | 0.001 | |||
| White | 679 (55.9%) | 4095 (60.4%) | 4774 (59.7%) | |
| Black | 74 (6.1%) | 469 (6.9%) | 543 (6.8%) | |
| Hispanic | 137 (11.3%) | 1104 (16.3%) | 1241 (15.5%) | |
| Asian | 289 (23.8%) | 938 (13.8%) | 1227 (15.4%) | |
| Unknown | 35 (2.9%) | 170 (2.5%) | 205 (2.6%) | |
| Annual household income, US$ | 0.02 | |||
| <$40,000 | 132 (10.9%) | 769 (11.3%) | 901 (11.3%) | |
| $40,000–$49,999 | 56 (4.6%) | 441 (6.5%) | 497 (6.2%) | |
| $50,000–$59,999 | 91 (7.5%) | 437 (6.4%) | 528 (6.6%) | |
| $60,000–$74,999 | 131 (10.8%) | 785 (11.6%) | 916 (11.5%) | |
| $75,000–$69,999 | 205 (16.9%) | 1147 (16.9%) | 1352 (16.9%) | |
| ≥$100,000 | 461 (38.0%) | 2631 (38.8%) | 3092 (38.7%) | |
| Unknown | 138 (11.4%) | 566 (8.4%) | 704 (8.8%) | |
| Patient residency region in US | 0.001 | |||
| Midwest | 97 (8.0%) | 657 (9.7%) | 754 (9.4%) | |
| Northeast | 259 (21.3%) | 931 (13.7%) | 1190 (14.9%) | |
| South | 561 (46.2%) | 3811 (56.2%) | 4372 (54.7%) | |
| West | 297 (24.5%) | 1377 (20.3%) | 1674 (21.0%) | |
| Y of TSH testing | 0.001 | |||
| 2010 | 198 (16.3%) | 1428 (21.1%) | 1626 (20.4%) | |
| 2011 | 231 (19.0%) | 1374 (20.3%) | 1605 (20.1%) | |
| 2012 | 227 (18.7%) | 1293 (19.1%) | 1520 (19.0%) | |
| 2013 | 276 (22.7%) | 1449 (21.4%) | 1725 (21.6%) | |
| 2014 | 282 (23.2%) | 1232 (18.2%) | 1514 (18.9%) | |
| Treating clinician specialty | 0.001 | |||
| OB/GYN | 557 (45.9%)a | 4021 (59.3%)b | 4578 (57.3%) | |
| Endocrinologist | 246 (20.3%)a | 402 (5.9%)b | 648 (8.1%) | |
| Primary care | 120 (9.9%)a | 437 (6.4%)b | 557 (7.0%) | |
| Other | 291 (24.0%)a | 1916 (28.3%)b | 2207 (27.6%) | |
| Key comorbidities | ||||
| Obesity | 74 (6.1%) | 339 (5.0%) | 413 (5.2%) | 0.23 |
| Diabetes mellitus | 29 (2.4%) | 179 (2.6%) | 208 (2.6%) | 0.61 |
| Hypertension | 35 (2.9%) | 323 (4.8%) | 358 (4.5%) | 0.02 |
| Recurrent pregnancy loss | 31 (2.6%) | 98 (1.4%) | 129 (1.6%) | 0.02 |
| History of thyroid disease | 86 (7.1%) | 226 (3.3%) | 312 (3.9%) | 0.001 |
a
Clinician with office visit closest to the date of LT4 prescription.
b
Clinician specialty identified from all office visits within 30 days of the index TSH date based on the following hierarchy: endocrinology, obstetrics/gynecology (OB/GYN), primary care, and other.