Free Thyroxine (Free T4)

For children under 1 year, do not feed for 30-40 minutes before the test. Do not eat for 2-3 hours before the test; still (non-carbonated) water is allowed. Avoid thyroid hormones and iodine preparations (as agreed with your doctor) for 72 hours before the test. Avoid steroid hormones (as agreed with your doctor) for 48 hours before the test. Avoid physical and emotional stress for 24 hours before the test. Do not smoke for 3 hours before the test.