Do I need to fast before my blood test?
Most blood tests did not require fasting. For example, kidney, liver, and thyroid function; blood counts, hormones, and infection blood tests are not affected by food.
What blood tests require fasting, and why?
- Glucose test, which measure blood sugar, to test for diabetes.
- Lipid test, which measure cholesterol, triglyceride, LDL and HDL. This is because after a meal, your glucose and triglyceride level will be higher, and not ideal to use as a reference point of your health.
- Iron test, which relate to some type of anemia. (Food tend to decrease iron level for some time)
How long, and how to do fasting?
- You should not take anything except water for 8-10 hours before a test.
- You should also avoid other beverages, gum, smoking, and exercise.
- You should ask a doctor if you need to stop your current medication. But most of the time, it is okay to take your usual medicines, unless they have to take with food, or need food afterward such as diabetic medicines.
Should blood tests be done in the morning?
Most blood tests can be done anytime of the day, except for some that benefit from testing in the morning.
- Hormone tests (especially cortisol and testosterone). Because many hormones fluctuate throughout the day, and usually peak in the morning.
- Some urine and sputum test. First morning urine and sputum are most concentrated, which is good for detecting things such as pregnancy, protein leakage in urine, and infection like tuberculosis and STD
When can you stop fasting?
As soon as your blood is taken, then you can eat or drink again. Some people find it useful to bring snacks so they have something to eat right after the test procedure is done.