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Blood Test: Fasting Before a Blood Test

Blood Test: Fasting Before a Blood Test

Fasting for a blood test is necessary, if the blood work is primarily done for a diagnostic purpose. To understand more on the fasting period, and other preparation tips, read on...
HealthHearty Staff
Last Updated: Mar 19, 2018
When we say blood test, it refers to a method wherein a blood sample is collected from an individual's vein for laboratory testing. It is probably one of the most frequently conducted medical tests. The objective of performing a blood test may vary from one person to another. For a healthy and disease free individual, a blood test is performed to check the blood type, hemoglobin, and other blood components. On the contrary, a patient may require blood testing to determine cholesterol levels, glucose levels, or presence of pathogens in the blood sample. This is when fasting before a blood test is instructed to get accurate results.

What is the Connection?

There are various types of blood tests, depending upon the approach for which the essaying has been done. For example, biochemical analysis of the blood is done to check the concentration of sodium, potassium, magnesium, chloride, bicarbonate, creatine, urea, and glucose. The readings of the blood test are then compared with the normal ranges prescribed for proper functioning of the body metabolic processes. In this way, a blood test is used to predict the overall health of a person.

It is to be borne in mind that not all blood tests call for fasting prior to the procedure. Types of blood test that require fasting are glucose test, cholesterol test (also referred to as lipid profile), and lactose tolerance test. Whatever be the case, many of us have a doubt as to how is a blood test and fasting related to each other? And why we need to fast for a specific period before a blood test? In order to get the answers of these queries, we need to understand the food digestion process.

Food after breaking down in simpler forms (glucose) by the digestive system is released into the bloodstream, which then circulates and helps in providing energy to the body cells. So, the amount of glucose present in the blood sample after having a large meal will be higher than any time of the day. Likewise, blood cholesterol and triglyceride levels measured before a meal is lower than the readings taken after a meal. In brief, consuming food before a blood work gives inaccurate results, which are influenced by the food type and amount of serving. Thus, a specific fasting period is recommended to get reliable results.

Fasting Guidelines

Apart from the doctor's expertise in conducting blood work, the responsibility of a candidate also plays a major role in getting correct blood test results. He/she should strictly follow the fasting guidelines as instructed by the physician or laboratory technician prior to drawing blood for examination. In most instances, the doctor performs the blood test procedure in the morning, so that it becomes easy for candidates to pass the fasting time. Some useful tips to be followed while fasting for a blood test are given below.
  • Usually, the period for fasting before blood test falls between 8 - 12 hours. However, the specific fasting duration may differ from one blood test to another.
  • Take a note of the things that may alter the test results. Some of these include tea, coffee, juice, chewing gum, soft drink, and smoking. As performing physical activities affects the test results, it may be wise to stop exercising during the said period.
  • Generally, drinking water during the fasting period is not restricted as it does not affect the blood test results. Also, for some fasting blood tests, the doctor may allow specific drinks, while restricting others.
  • As for taking regular prescription medication during the fasting time, one should discuss it with the concerned doctor. Most likely, the doctor will ask to continue taking it.
  • It is best to stick to the rules of blood test, fasting, and other tips, as recommended by the doctor. Any failure to abide the rules should be consulted with the doctor beforehand.
  • While speaking about fasting blood glucose test, the candidate should not consume anything (except water) for 12 hours before the blood test.
  • Blood work for triglyceride level testing may require 12 hours of fasting before the procedure. In some cases, 14 hours fasting is necessary.
  • In order to check cholesterol levels, the doctor may suggest a candidate to fast for 9 - 12 hours before the blood sample is drawn.
In a nutshell, fasting before blood test is crucial to get accurate results and diagnose the underlying medical problem correctly. If necessary, the doctor may suggest further treatment methods based on the blood test results to improve the health condition of the person.