Table 1.
Baseline patient demographics and clinical characteristics in the matched cohorts
| Demographic and clinical characteristics | Synthroid persistent users (n = 18,382) |
Generic levothyroxine persistent users (n = 18,382) |
Standardized differencea |
|---|---|---|---|
| n (%)/mean (SD) | n (%)/mean (SD) | ||
| Age at index (years), mean (SD) | 53.4 (12.13) | 53.4 (11.77) | 0.000 |
| Age categories, n (%) | |||
| 18–39 | 2100 (11.4) | 2046 (11.1) | 0.009 |
| 40–64 | 13,806 (75.1) | 14,152 (77.0) | –0.044 |
| 65–74 | 1629 (8.9) | 1407 (7.7) | 0.044 |
| 75 + | 847 (4.6) | 777 (4.2) | 0.019 |
| Female, n (%) | 15,083 (82.1) | 15,085 (82.1) | 0.000 |
| Health plan type, n (%) | |||
| PPO | 10,919 (59.4) | 10,270 (55.9) | 0.071 |
| HMO | 5769 (31.4) | 6154 (33.5) | –0.045 |
| CDHP | 1694 (9.2) | 1957 (10.6) | –0.048 |
| Medicare Advantage plan, n (%) | 1442 (7.8) | 1390 (7.6) | 0.011 |
| Geographic region of patientb, n (%) | |||
| Northeast | 5176 (28.2) | 5028 (27.4) | 0.018 |
| Midwest | 2313 (12.6) | 2291 (12.5) | 0.004 |
| South | 6835 (37.2) | 6937 (37.7) | –0.011 |
| West | 4056 (22.1) | 4125 (22.4) | –0.009 |
| Prescribing/treating physician specialtyc, n (%) | |||
| PCP | 10,104 (55.0) | 10,388 (56.5) | –0.031 |
| Endocrinologist | 4961 (27.0) | 4604 (25.0) | 0.044 |
| Others/unknown | 3317 (18.0) | 3390 (18.4) | –0.010 |
| Comorbidities | |||
| QCI, mean (SD) | 0.5 (1.10) | 0.5 (1.06) | 0.005 |
| Other comorbidities of interest, n (%) | |||
| Alopecia | 347 (1.9) | 335 (1.8) | 0.005 |
| Anemia | 1590 (8.6) | 1580 (8.6) | 0.002 |
| Celiac disease | 59 (0.3) | 41 (0.2) | 0.019 |
| Constipation | 363 (2.0) | 401 (2.2) | –0.014 |
| Goiter | 2497 (13.6) | 2353 (12.8) | 0.023 |
| Hyperlipidemia | 7292 (39.7) | 7373 (40.1) | –0.009 |
| Hypertension | 5763 (31.4) | 5761 (31.3) | 0.000 |
| Inflammatory bowel disease | 99 (0.5) | 116 (0.6) | –0.012 |
| Obesity | 1051 (5.7) | 1195 (6.5) | –0.033 |
| Psoriasis | 147 (0.8) | 140 (0.8) | 0.004 |
| Rheumatoid arthritis | 273 (1.5) | 288 (1.6) | –0.007 |
| Urticaria | 145 (0.8) | 147 (0.8) | –0.001 |
| Laboratory testing | |||
| Patients with TSH resultd, n (%) | 11,909 (64.8) | 11,795 (64.2) | 0.013 |
| TSH result, mean (SD) [median], mIU/L | 5.0 (11.82) [2.6] | 5.6 (13.01) [2.9] | –0.048 |
| TSH results between 0.3 and 4.12 mIU/L, n (%) | 6919 (37.6) | 6440 (35.0) | 0.054 |
CDHP consumer-driven health plan, HMO health maintenance organization, PCP primary care physician, PPO preferred provider organization, SD standard deviation, TSH thyroid-stimulating hormone, mIU/L milli-international units per liter
aStandardized difference = difference in means or proportions divided by the pooled standard deviation. An absolute value of the standardized difference < 0.1 was used to indicate balance in a variable across the cohorts
bFor the remainder, geographic region information was not available
cOn index prescription claim
dMost recent serum TSH result in the 6-month pre-index period