do you need to fast for thyroid blood test?
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Generally, you don't need to fast before doing a thyroid function test. However, not fasting is sometimes linked to a lower TSH level. This means your results might not pick up on mild (subclinical) hypothyroidism — where your TSH levels are only mildly elevated.
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For example, measurements of kidney, liver, and thyroid function, as well as blood counts, are not influenced by fasting. However, fasting is required before commonly ordered tests for glucose (blood sugar) and triglycerides (part of the cholesterol, or lipid, panel) for accurate results.
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Fasting before certain blood tests is important to help make sure that your test results are accurate. The vitamins, minerals, fats, carbohydrates, and proteins that make up all food and beverages can impact blood-level readings, clouding the results of your test.
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Fasting before blood tests Fasting means that you eat and drink nothing except water for 8 –16 hours before your blood test (12 hours optimal).
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Fasting before a blood draw means you don't eat or drink anything except water. Don't wait until the day of your blood draw to ask if you should fast. That could cause your appointment to be rescheduled. If at any point you're unsure if fasting is required, contact your doctor.
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How often and when should I test? You may need to test your blood several times a day. Generally, these times are fasting (first thing in the morning before you eat) and 2 hours after each meal. Occasionally, you may be asked to test more frequently during the day or at night.
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Typically, fasting for 9-12 hours (drinking water only) before having your blood drawn is required, but some healthcare practitioners allow non-fasting lipid testing. In particular, children, teens and young adults (ages 2 to 24) may have testing done without fasting.
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If your blood sample is being tested only for a complete blood count, you can eat and drink normally before the test. If your blood sample will be used for additional tests, you may need to fast for a certain amount of time before the test.
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So a blood test can be used to determine the amounts of hormones produced by the thyroid gland. The blood test measures the levels of TSH and the thyroid hormones triiodothyronine (T3) and thyroxine (T4). A change in the TSH level can be an early sign of a thyroid problem.
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With certain blood tests, you may be instructed to fast for up to eight hours before your appointment. Fasting before a blood draw means you don't eat or drink anything except water. Don't wait until the day of your blood draw to ask if you should fast.
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You can eat and drink as normal before some blood tests. But if you're having a "fasting blood test", you will be told not to eat or drink anything (other than water) beforehand.
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Determine When Taking Levothyroxine is Best for You “For that reason, it's recommended to wait 30-60 minutes after taking the thyroid hormone before you have breakfast, particularly for those with thyroid cancer, pregnant women, and those sensitive to thyroid fluctuations.”
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Common fasting blood tests an iron blood test (used to diagnose conditions such as iron deficiency anaemia) – you fast for 12 hours before the test.
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The RF test doesn't require any food, drink, or medication restrictions, nor do the other tests you may have with it. If you have different blood tests than those mentioned here, you may need to fast before the test.
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Studies have shown that early morning fasting causes higher TSH levels compared to tests taken in the afternoon on patients that did not fast. Since fasting affect TSH levels, fasting might make it difficult to diagnose subclinical hypothyroidism, as the condition is diagnosed by specifically looking at TSH levels.
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an iron blood test (used to diagnose conditions such as iron deficiency anaemia) – you fast for 12 hours before the test.
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Your doctor may recommend fasting before having your cholesterol checked. If they say you should fast, they'll likely suggest that you avoid eating for 9 to 12 hours before your test. For this reason, cholesterol tests are often scheduled in the morning.