Table 2.
Definition of Subclinical Hypothyroidism and Atrial Fibrillation Events
Study | Cohort TSH and fT4 Reference Range |
Definition of Subclinical Hypothyroidism in IPD Analysis | AF Events – Methods of Ascertainment |
---|---|---|---|
| |||
United States | |||
Cardiovascular Health Study | TSH 0.45–4.50 mIU/L, fT4 9–22 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.7–1.7 ng/dL (9–22 pmol/L) or missing fT4 (0/436, 0%) | Self-report, annual ECGs, ICD-9 coded AF on hospital discharge |
Health ABC Study | TSH 0.1–4.4 mIU/L, fT4 10.3–23.2 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.8–1.8 ng/dL (10.3–23.2 pmol/L) or missing fT4 (195/270, 72%) * | Minnesota-coded ECGs at baseline and at year 4 follow-up, ICD-9 coded ambulatory and inpatient AF diagnoses from CMS data |
Osteoporotic Fractures in Men (MrOS) Study | TSH 0.55–4.78 mIU/L, fT4 9–24 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.7–1.85ng/dL (9–24pmol/L) or missing fT4 (0/46, 0%) | ECG at baseline, self-report, AF diagnoses from medical records every 4 months |
Europe | |||
Bari Study | TSH 0.35–5.50 mIU/L, fT4 9–23.2 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal FT4 0.7–1.8 ng/dL (9–23.2 pmol/L) or missing fT4 (0/23, 0%) | ICD-9 coded AF on hospital discharge |
Leiden 85+ Study | TSH 0.3–4.8 mIU/L, fT4 13–23 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 1.0–1.8ng/dL (13–23 pmol/L) or missing fT4 (1/27, 3.7%) | Minnesota-coded annual ECGs |
Study of Health in Pomerania | TSH 0.25–2.12 mIU/L, fT4 8.3–18.9 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.64–1.47ng/dL (8.3–18.9 pmol/L) or missing fT4 (0/12, 0%) | Minnesota-coded ECGs at baseline, year 5 and year 10 follow-up |
Invecchiare in Chianti Study | TSH 0.46–4.68 mIU/l, fT4 9.9–28.2 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.77–2.19ng/dL (9.9–28.2pmol/L) or missing fT4 (0/26, 0%) | ECGs at baseline, 3 year, 6 year and 9 year follow-up |
Rotterdam Study | TSH 0.4–4.0 mIU/L, fT4 11–25 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.9–1.9ng/dL (11–25pmol/L) or missing fT4 (29/91, 31.9%) | ECGs at baseline, year 2 and year 7 follow-up, ICD-10 coded AF diagnoses from GP records and hospital discharge |
PROSPER Study | TSH 0.45–4.50 mIU/L, fT4 12–18 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.9–1.4 ng/dL (12–18pmol/L) or missing fT4 (211/384, 54.9%) † | Minnesota-coded annual ECGs |
EPIC-Norfolk | TSH 0.4–4.0 mIU/L, fT4 9–20 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.7–1.6ng/dL (9–20 pmol/L) or missing fT4 (0/607, 0%) | Self reported intake of drugs used for AF treatment at baseline (digitalis and VKAs), ICD-10 coded AF on hospital discharge |
Australia | |||
Busselton Health Study | TSH 0.4–4.0 mIU/L, fT4 9–23 pmol/L | TSH ≥4.5 mIU/L & TSH <20mIU/L, normal fT4 0.7–1.8ng/dL (9–23 pmol/L) or missing fT4 (1/ 37, 2.7%) | Minnesota-coded ECGs at baseline and at year 14 follow-up |
Abbreviations: AF, atrial fibrillation; ECG, electrocardiogram; EPIC, European Prospective Investigation of Cancer; fT4, free thyroxine; GP, general practitioner; ICD, International Statistical Classification of Diseases and Related Health Problems; IPD, individual participant data; PROSPER, Prospective Study of Pravastatin in the Elderly at Risk; TSH, thyroid stimulating hormone, VKA, vitamin K antagonist.
fT4 was measured only in participants with TSH ≥ 7.0 mIU/L or TSH in this cohort
fT4 was measured only in participants with TSH ≥4.5mIU/l in this cohort