The Importance of Fasting Before a Blood Test: Key Facts You Should Know

Fasting before a blood test is often a common instruction given by a doctor in most cases. This means you should not drink or consume anything except water from at least 8 to 12 hours before the test. However, fasting is not a compulsory instruction for every test, only specific tests require fasting. Before undergoing a blood test in London, you must be aware of when fasting is necessary and how it affects the accuracy of some blood tests.

Fasting is not that easy, not even for medical purposes. This blog highlights the blood tests which require fasting, how to fast safely, and how fasting impacts specific blood tests.

Which blood tests need fasting?

Here are the blood tests that usually require fasting:

Blood cholesterol tests

Also known as lipid profiling, blood cholesterol tests determine the cholesterol and fatty acid levels in your body. High fatty acid levels in your blood suggest greater risks of developing heart conditions and other heart diseases. The fatty substances tested in the blood cholesterol test include looking at high density lipoprotein (HDL), low density lipoprotein (LDL), and triglyceride levels.

This test requires fasting from at least 9 to 12 hours before to achieve accurate results. If you consume anything before this test, it produces inaccurate results due to increased levels of these fatty substances in your blood. You must also strictly avoid alcohol at least 24 hours before from undertaking the test.

Some recent guidelines suggest that fasting is not essential for all types of cholesterol tests. Consult your doctor to find out if you should follow the new guideline or fast for your cholesterol test.

Fasting blood glucose test

The purpose of fasting blood glucose test is to measure the glucose or sugar level in the blood, both for diabetic as well as pre-diabetic patients. Diabetes suggests a condition of high sugar or glucose level in your blood. This test requires fasting at least 8 hours before to deliver accurate results which are important to diagnose diabetes.

Iron tests

Iron test is used to evaluate the level of the mineral, iron in the blood. It helps in diagnosing iron related conditions like anaemia. Iron test requires fasting from at least 12 hours before for accurate results.

A wide variety of foods contain iron, and it can get easily absorbed into blood. This is why eating anything prior to the test can increase your iron level, leading to inaccurate result. Not only food items, make sure to avoid any mineral or iron supplement from 24 hours before the test.

Gamma-glutamyltransferase (GGT)test

The level of the Gamma-Glutamyltransferase (GGT) enzyme in your blood is measured by a GGT test. Remember that high GGT levels indicate a liver disease, a bile duct problem, or alcohol abuse. Eating food, drinking alcohol, smoking or even your ongoing medications can impact your test results. Consult your healthcare provider of which medicines to avoid before undergoing the test.

Vitamin B12 test

This test measures the amount of vitamin B12 in the blood and is often used to diagnose specific types of anaemia. Fasting for at least 6 to 8 hours before the test is crucial for achieving accurate results. In fact, intaking certain medicines might also interfere with the results’ precision. Make sure to inform your doctor about any medication you are taking.

Renal function panel

This test helps checking the state of your kidneys. It requires fasting from at least 8 to 12 hours from before the test.

Comprehensive or basal metabolic tests

This test checks for the proper functioning of the liver and kidneys, and also determines your blood glucose or electrolyte level or fluid balance in the blood. You must fast from at least 10 to 12 hours prior to this test.

Why should I fast?

When you intake any kind of drink or food, digestion of that leads to assimilation of the nutrients in the bloodstream. As a result, your nutrient levels like amino acids, sugars, minerals such as iron, fatty substances including cholesterol, enzyme levels like GGT increase in the blood. Measuring the accurate levels of these substances helps in diagnosing conditions like diabetes, heart, kidney, or liver problems.

The accuracy of these blood test results is often affected by eating or drinking as these interfere with the nutrient balance in the body.

How to fast safely?

• Staying hydrated is extremely important. You must drink plenty of water for this. Water does not influence the test results in any way, and this is the only thing you can ingest while fasting.
• Next it is important to be aware of the number of hours you should fast for a specific blood test. This helps you easily evaluate the last time you can eat or drink anything. For example if you require 8 hour fasting before your test and your scheduled test time is at 8 am, you must not have anything after midnight.
• You must also inform your doctor about your every ongoing medication so that they can guide you the best regarding their effect on the test result. Consult your doctor to find out which medications you should avoid before taking a blood test.

Besides cutting down on foods and drinks you must also avoid the following to get accurate test results:

• Exercise and strenuous activities: Exercise or strenuous jobs can raise metabolic reactions in your body. A high metabolic activity speeds up absorption of nutrients and digestion process which affect your test results.
• Coffee: You must avoid coffee while fasting as it also affects digestion.
• Smoking: Consumption of tobacco also impacts the fasting process.
• Chewing gum: Chewing gums speed up digestion as well. Moreover, chewing gums contain sugar which alters the blood glucose level s well.
• Alcohol: Alcohol again affects the fat and sugar levels in your blood, disrupting the accuracy of the test results.

Conclusion

A wrong diagnosis might lead to health complications as the inaccurate blood tests results can misguide doctors. If you are looking forward to get a blood test in London and need to fast before it, the above information is there to guide you. Consider rescheduling your blood test appointment if you eat or drink anything while fasting.