Fasting Blood Test Explained – What to Expect
Fasting blood tests happen if your doctor requires you to fast before a blood test. The number of hours you need to fast will depend on the kind of tests that will be carried out.
Fasting glucose, for example, recommends fasting for 8 hours, while fasting for cholesterol/lipid testing recommends fasting for 12 hours.
Whichever is the case, it is important not to eat or drink, other than water, for the prescribed fasting hours.
Why fast before a blood test?
This will help ensure that your test results are accurate.
Food and beverage contain proteins, carbohydrates, minerals, vitamins, and fats that can have an impact on the blood-level readings and cloud the test results.
Why is water allowed and not other beverages?
This is because water hydrates your veins and make them easier to find and draw blood from. This is why you need to stay hydrated and drink plenty of water before a blood test, whether fasting is required or not.
However, it is also important not to fast longer than 12 hours as doing so can also affect the test results.
Smoking should also be avoided when fasting for a blood test.
If you are taking prescribed medications, your doctor will advise you whether to continue or discontinue using them while fasting. So make sure to consult your doctor.
Which blood test requires fasting?
Blood Glucose Test
This measures the amount of glucose in your blood and is primarily done to check for type 1 and type 2 diabetes and gestational diabetes. An increase in blood glucose levels could mean you have diabetes.
Blood glucose test is also done to test for hypoglycemia, the opposite of a high blood glucose level.
Liver Function Test
Want to know how healthy or unhealthy your liver is? Have a liver function test performed to measure the levels of liver enzymes, proteins, or bilirubin in your blood.
This test is done to screen for liver infection, monitor side effects of certain medications, measure the degree of liver scarring, when experiencing symptoms or already have a liver disease, and when planning to get pregnant.
Complete Cholesterol Test
Also called lipid panel or lipid profile, this test is done to measure the amount of good and bad cholesterol and triglycerides present in your blood. This includes triglyceride level test, high-density lipoprotein (HDL) level test, and low-density lipoprotein (LDL) level test.
- Testing for triglyceride levels will help determine your risk of developing heart disease and atherosclerosis.
- Testing for high-density lipoprotein measures the level of your blood’s good cholesterol.
- Testing for low-density lipoprotein measures the level of bad cholesterol in your blood, increasing the risk for heart disease.
Basic Metabolic Panel
This is done to help assess your body’s important functions. It is made up of blood (serum) test for blood urea nitrogen (BUN), creatinine, glucose, albumin, carbon dioxide or bicarbonate, calcium, sodium, potassium, and chloride.
Renal Function Panel
This is performed to test for kidney function and is usually included as part of a general health screening. This is also ordered for someone that is showing symptoms of or is treated for kidney disease.
Lipoprotein Panel
This test is done to measure the levels of lipoprotein in your blood. If the levels are 31 – 50 mg/dL (75 – 125 nmol/l) or > 50 mg/dL (> 125 nmol/l), your risk for heart disease is high or very high, respectively.
