Can A Cold Mess Up A Blood Test?

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If aggravated, the common cold may affect your white blood cell count and render your blood test results inaccurate. Your blood test results can also be impacted by natural or artificial causes such as menstruation and alcohol consumption, respectively. 

Your dos and don’ts before a blood test will largely depend on which kind of blood test you’ll be taking since tests involving cholesterol will need fasting, while liver-function tests don’t need fasting. 

However, precautions such as staying away from alcohol and tobacco may apply to any blood test. If you’re going through a difficult cold, you can try out various home remedies like staying hydrated with warm liquid foods and getting as much rest as possible. If your cold has aggravated symptoms of the flu, then you might need the assistance of a doctor to recover completely.

Blood tests are widely practiced to diagnose various potential disorders, possible deficiencies, or complications in your health. Your blood is drawn from your vein and is then processed in the laboratory for any such complications.

Since we’re talking about the intricacies of our inner body, even the simplest factor that you’re not so concerned about may potentially impact and mess with the blood test results that you expect.

So, it’s crucial to know the proper procedures and precautions involved with blood tests, especially if you’re going through even the mildest of all illnesses like the common cold before taking part in the blood test.

Can a cold mess up the results of your blood test? What other significant aspects can cause a blunder in your blood test results? What are the dos and the don’t involved in preparation for a blood test? What can you do about your cold before taking part in a blood test? How can you know if you’re cold is developing into the flu?

Can a cold mess up a blood test?

You need to know that when you’re suffering from a cold as a result of a virus or bacterial infection, your white blood count increases to fight off the illness.

A woman with the common cold is blowing her nose to get rid of mucus

This might be why you notice that your blood test doesn’t come out as accurate due to the sudden change in your white blood count. It’s always advised not to do a blood test when you’re having a temporary ailment of some sort.

What can mess with your lab test results?

Apart from a cold, there are other aspects that you should consider which may mess with your blood test results, as given below.

  1. Caffeine – Caffeine-included beverages could definitely affect your blood test results, depending on the quantity that you have consumed. This is mainly because such beverages like black tea and coffee are well-known diuretics, which would mean that they impact the speed of your digestion process.
  2. Alcohol & Tobacco – Alcohol increases liver enzymes and blood sugar levels in your body, and if your blood test involves the need for fasting, it will most surely affect your results. Tobacco too elevates your blood sugar, cortisol, and triglycerides; and should therefore be avoided.
  3. Medications – Various over-the-counter medicine can impact the accuracy of your blood test results, which is why you should always ask for permission from your doctor about the medications that you take before a blood test. The common types of medications that you may need to stay away from would be antibiotics, antidepressants, steroids, and Acetaminophen.
  4. Physical exercise – Your average intense workout may stress your body and induce changes in your glucose production that could stay up for a few hours even post-workout. Your red blood count, creatine kinase levels could also be increased and affect your blood test results.
  5. Dehydration – If you’re not hydrated enough, it might cause potassium imbalances in your blood test results.
  6. Natural biological causes – If you’re going through a pregnancy, puberty, menstruation, or even menopause, it might affect the results of your blood test due to the changes in hormonal activities in your body. However, doctors do take these natural factors into account before conducting the test.

Dos and don’ts before a blood test

It’s best to take extra measures to ensure a smooth blood test process and accurate results.

For this, you may need to impose restrictions on yourself to strictly adhere to the rules given to you by your doctor.

The DosThe Don’ts
Stay hydrated. Some blood tests even require you to drink more water to maintain more fluids in your veins.Avoiding cooked meats, caffeine, alcohol
Some blood tests specifically need fasting as a preparation, like blood glucose, cholesterol, liver function tests.Preventing from smoking, including second-hand smoke
Unless fasting is needed, make sure you eat a healthy breakfast to keep your blood sugar raisedAvoiding strenuous exercise or sexual activity
Right after your blood test, have a snack if you’ve engaged in fasting.Temporarily pausing over-the-counter medications and supplements.

If you want to avoid running the risk of getting a cold at all before a blood test, a Cochrane Systematic review reveals that hand-washing, use of alcohol-based disinfectants have significantly reduced the risk of developing common cold infections.

What can you do about your cold before a blood test?

A woman with the cold is resting on the sofa after taking medicine to relieve her symptoms.

The best thing that you could do is to postpone your blood test so that you can permanently heal from your common cold.

According to a 2014 study conducted by the US National Library of Medicine, a cold may peak at 3 to 4 days and last for a total duration of 7 to 10 days. Various home remedies can help soothe away your cold within a few days.

  1. Rest – This is the most crucial thing to do since most often your body just needs enough rest to fight off a cold.
  2. Hydration – Try and drink a lot of warm fluids which will help treat your cold. Even if you’re drinking water, drink warm water.
  3. Moisture the air – A moist vaporizer or even a humidifier will help in this task. The purpose of this is to loosen up your nasal congestion so that you can breathe easier during a nose block.
  4. Over-the-counter medicine and cough syrups – These will be useful if you’re cold doesn’t seem to go down in a few days and if you develop a cough out of the cold as well.
  5. Appropriate foods – Sometimes you might not feel like eating at all when you’re ill, but foods like warm soups, yogurt, and hot tea will boost your recovery.
  6. Warm baths – If you’re experiencing mild fever, you’ll benefit a lot from having a simple warm bath as it helps to soothe your body aches involved with fever.
  7. Saltwater gargling – This will help you out a lot if you’re experiencing a sore throat from your cold. Warm salt water gargling will give you almost immediate relief. A 2014 study conducted among cold patients revealed that gargling water proved to reduce the risk of upper respiratory tract infection by 40%.

How can you know if your cold is developing into the flu?

Unlike the common cold, the flu is somewhat an aggravated cold caused by a virus. Since both are known respiratory illnesses, it might be difficult to differentiate the two at first.

Both these ailments share fundamental symptoms like body aches, stuffy or runny noses, and sneezing.

However, the main factor distinguishing the two is that flu symptoms seem far more aggravated than common cold symptoms.

The common cold doesn’t really lead to more additional health conditions, while the flu can often end up with sinus infections, sepsis and can even develop to the stage of pneumonia. The best way to properly distinguish the two is by seeking medical tests from your doctor to confirm your suspicions.

While the cold can be easily treated by home remedies, as mentioned, you’ll have to take various prescribed medications when it comes to the flu.


Blood tests are the most efficient ways that doctors evaluate how well your essential organs such as kidneys, heart, liver, thyroid are functioning.

This makes it all the more important to take precautionary measures before taking a blood test to ensure its accurate result.

If you don’t follow the direct instructions of your doctor, your blood test will have to be set aside and retaken. So it’s always best to be honest with your doctor when or if you have derailed from your direct instructions to avoid confusion with the test results.

Since your doctor’s evaluation of the results will determine your diagnosis, you’ll need to do your part of the task quite diligently.

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Kavisha Rodrigo
I'm a sports person that enjoys researching into pushing the limitations of the human body. When it comes to health, I'm a big fan of working out and staying healthy. For hobbies, I'm a big fan of Pokemon and Coldplay.

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