One day or the other, we are all bound to take a blood test – as part of a general check-up, an employment-based medical test, screening based on certain symptoms, evaluation of organs and their performance, pregnancy, infections, deficiencies, genetic mutations etc. Fundamentally, a blood test reveals specific conditions of the body that may not be easily accessible otherwise.

Blood tests are usually recommended from a form in which almost all kinds of tests have been pre-listed, generally without instructions on how to prepare for the specified test. A majority of us end up calling the laboratory to find out, and the famous question is “can I have tea or coffee before coming for my test”. This comes mostly from patients who take the morning blood test.

There is a certain percentage of patients almost every day who have their appointments rescheduled for not following the prerequisites of a blood test. Let’s explore the basics.

Taking A Blood Sample

The person who collects a blood sample from a patient as part of a medical test is known as a phlebotomist.

The phlebotomist draws blood, usually from the arm, by fastening a band just above the site of puncture, inserting a needle into the vein and drawing the required quantity of blood. He labels it separately according to the type of tests opted for and sends the blood samples for testing.

Some Blood Tests Need Preparation

Fasting and suspension of certain medications are the two main prerequisites for particular blood tests to facilitate accurate results. Food and medicine can interfere with nutrient levels, making it difficult for the physician to detect abnormalities if any.

Fasting is the abstinence of food and drink for about 8-12 hours, depending on the type of test recommended.  Early morning tests are taken after the patient has fasted, and sleeping time is calculated as fasting hours. However, drinking water is allowed.

Suspension of Certain Medication is advised as some medicines can alter results and hence compromise on accuracy.

Which Blood Tests Require Fasting?

S #	Test	Intention	Required Fasting Hours
1	Blood Glucose Test.	Checks if blood sugar levels are at a healthy level.	8-10
2	Gamma Glutamyl Transferase (GGT).	Evaluates liver health.	8-10
3	Glucose Tolerance Test.	Checks how the body mobilizes sugar to the tissues.	8-12
4	Liver Function Test.	Evaluates enzymes and substances made by the liver.	8-12
5	Renal Function Test.	Assesses kidney function.	8-12
6	Vitamin B12 Test.	Checks the overall vitamin B12 store.	8-12
7	Lactose Tolerance Test.	Determines a person’s tolerance level of dairy products.	8-12
8	Lipid Profile.	Assesses the amount of cholesterol and triglycerides in the blood.	12
9	Thyroid Function Test.	Measures the functioning of the thyroid glands.	12
10	Iron Test.	Measures iron level and deficiency.	12

Points To Remember When You Are Scheduled For A Blood Test

Water is allowed for a blood test on fast. Juice, tea and coffee, though fluids are not allowed.

Being hydrated by drinking water makes the drawing of blood easier.

Chewing gum or betel leaves, smoking, popping multivitamins or supplements and doing strenuous exercise should be avoided.

Get good sleep the previous night as lack of sleep can affect a blood test.

Remaining calm helps a lot.  The phlebotomist knows his job.