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How to Prepare & Fast Before A Blood Test

Medically Approved by Dr. Edward Salko

Table of Contents

Morning. Attractive woman with glass of water

So, you’ve decided to get some blood work done.

First and foremost: Bravo!

This is probably one of the best decisions you can make to take control of your health and well-being – and is the first step in putting your health in your hands.

Most simply put, under normal circumstances, every element of our blood is present in a specific concentration, and maintaining the right proportions of all elements is critical for normal bodily function and well-being.

But before you know how to prepare for your blood test and understand its results, it’s important to know what, exactly, a blood test is.

What A Blood Test Is

Blood tests keep track of your blood chemistry and bodily functions. During a blood test, a trained lab technician will take a sample of your blood, with the quantity taken depending on the type of test and the number of assessments that have to be done. 

The blood sample is then taken to a lab and analyzed, either under a microscope to check the number and shape of the different blood cells or chemically to look for substances, like glucose or certain proteins and validate the person’s blood group, blood clotting time, blood cholesterol, and more.

To check for any infections, blood is tested for the presence of antibodies that are produced by the immune system to ward off bacterial or a viral infection.

Diseases, for example, can cause an imbalance in the blood’s chemistry. An infection promotes an increase in immune cells, while anemia can be observed with a decline in the number of red blood cells or lower hemoglobin levels. Even problems with other organs, like the liver and kidney, can cause the levels of certain enzymes or substances – like creatine – to increase and can be diagnosed by blood test.

More specifically, each type of disease-causing germ causes the body to release a particular antibody. By observing these antibodies in the blood, a diagnosis can be made on the exact type of infection.

Blood tests can also check for the presence of certain hormones and growth factors, like in those of a pregnancy test that can confirm whether or not a woman is pregnant.

But listen: We understand that even if you’re not afraid of blood or needles, having your blood drawn may not be nestled snugly at the top of your ‘Things I Love To Do’ list. So here are some tips to make it a teeny bit easier.

Preparing For A Blood Test: The Details

Depending on what blood test you’re getting done, you will be given instructions beforehand. And the most important way to prepare for a blood test? Keep calm and have someone for moral support if you think you’ll need it.

Here are additional common considerations, requirements and things to consider:


Many blood tests, such as cholesterol tests, require fasting for accurate results. This means no food or drink (besides water) for 8-12 hours before the test (including chewing gum and even breath mints!). So nothing after dinner, and no breakfast in the morning before you go to the lab.

Fasting is also required when your glucose levels are being tested. Usually, your blood is drawn twice – once when you’re on an empty stomach and a second time about two hours after eating. However, it is important to remember that fasting only means not consuming food or drinks with any calorific value; you can still drink water.

A simple guide is to use 12 hours as your measurement. If your plan to go to the lab at 8 a.m., start fasting at 8 p.m. the night before.


Even if you’ve been instructed to fast, drinking water at regular intervals before a blood test is recommended. When you are well-hydrated, it makes it a lot easier for your veins to be located and the blood to be drawn. But at the same time, don’t go overboard with your water intake as that could affect the electrolyte balance in your blood and interfere with the test results.

So drink water before you go to bed and then before you have your blood drawn is a good idea so that you’re not dehydrated. Then, have another glass or two after you’ve had your blood taken to replace your fluids.


For a few tests, you will also be required to stop taking certain medications for some time before the test. For example, if you are on a hormonal pill, you might have to avoid taking the pill for 24 to 48 hours before the blood test so your natural hormonal levels may be checked without any interference from the changes caused by the medication.

Also, be sure to inform the prescribing doctor or technician about any medication you are currently taking to be safe.

Medical Conditions:

You will also need to inform the prescribing doctor or technician about any conditions you might have. In some cases, an ongoing chronic disorder can affect the test results for another condition, giving you a false positive or negative.

And no matter how small or insignificant you might think a problem is, it’s always better to inform the person administering the test about it. If you have any questions, be sure to ask them before your blood is drawn. 


Especially for a fasting blood test, try to get to the lab first thing in the morning. Some labs open at 7 a.m. or even earlier. If you wake up hungry or normally feel weak before you eat breakfast, bring juice or a snack with you to the lab to enjoy after your blood has been drawn.


If you’ve already ordered and paid for your test through Personalabs, you’ve completed all of the paperwork. Bring your confirmation lab order and your photo ID with you. The lab will verify your information for your protection.


Your phlebotomist is a lab technician specifically trained to draw blood. They will usually ask you which arm you prefer for the venipuncture. A tourniquet will be applied to your arm, and they will feel your arm for a vein – which for some people may be hard to find. But don’t worry – phlebotomists know what they’re doing.


Once your phlebotomist has found a vein, they will tell you what they need you to do. They’ll insert a needle – which will pinch or sting a bit – and then give you instructions. Be sure to follow them.


It may be hard to relax while you’re having your blood taken, but try not to pull away or move around. If you’re squeamish, don’t watch as your blood is drawn. And if you start to feel nervous or light-headed, focus on just one thing: breathing.


Many times a phlebotomist will fill more than one tube of blood – but the tubes only hold about a teaspoon each, so there’s no need for concern. You won’t be bled dry! Promise.


After the needle is removed, a bandage will be applied to your arm. Again, follow the phlebotomist’s instructions. Even if you think you’ve stopped bleeding, removing the bandage too soon could result in bruising.


You’re done! Congratulations. The whole process probably only took a few minutes. Now – especially if you’re rushing off to work – don’t forget to enjoy a nice breakfast and lunch to give you energy.

After The Blood Test: Understanding Your Results

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The Language:

How’s your albumin level? What is your BUN/creatinine ratio? Your routine blood tests can seem cryptic so deciphering them can prove daunting. As such, it’s important to learn what those numbers and abbreviations really mean. Learning to understand these complicated shorthanded abbreviations can yield both insights into your health and help you spot and fix issues or deficiencies.

The Time:

Your results can take time – up to 2-3 days in many cases. If you haven’t heard back from the lab in the first 24 hours, it could be because your tests need more time to complete. This is especially true when checking for bacterial cultures. Usually, the lab will inform you about when you can expect your results at the time of taking your blood. So if you don’t hear back immediately, that isn’t necessarily reason to panic.

The Doctor:

If your test results show your values to be outside of the normal range, then we suggest talking to your doctor. While we encourage you to be informed about your test results, you should never draw any conclusions or make any assumptions if you’re not a physician.

The Panic:

Any number of circumstances must be considered before any conclusions are drawn from your blood test results. So it’s best to not panic, even if something doesn’t look quite right. Your doctor is the best person to explain your results and interpret them for you, discussing treatment options as needed.

The ‘Not Normal:’

An abnormal blood test result could mean any number of things. Medications you were taking for a cold could be a factor. A woman’s menstrual cycle might be the culprit. Any allergies or possible hereditary factors could skew the numbers. Again, when in doubt – or panic – talk to your doctor.

The Patient’s Age:

Your blood results today will likely not mirror those from 10 years ago – and this is totally normal. Age can play a role in altering blood chemistry, and some results may vary but still be ‘normal’ for your current age. 

The Mistakes:

While rare, you could potentially get an incorrect result. The two most common reasons are due to a mix up of blood samples and the contamination of a sample before testing. Again, while exceptionally rare, your doctor may order a retest if the test results are blatantly inconsistent with your symptoms.

The ‘Positive:’

While in real life a ‘positive’ is a good thing, the opposite is – confusingly – true in blood tests. A positive result could denote the presence of an infection or some type of disease. 

The ‘Negative:

Again, as opposed to real life, medically speaking, a ‘negative’ is usually a good thing – unless you were hoping to be pregnant and aren’t – or are ‘negative,’ of course. 

Blood Testings With Personalabs: With You Every Step of the Way

For more than 13 years, we’ve been committed to providing our patients with high-tech lab testing services that are convenient and easy to access. Our wide range of blood tests with highly accurate results through our partner labs are affordable and accessible – and all without a doctor’s assistance. 

With Personalabs, you get the lab tests, medications, and answers you want – when you want them, to put your health in your hands. Take control of your health today!

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