10 May 2023

What can affect your blood test results?

What can affect your blood test results?
Medically reviewed by Dr Anojan Arulananthan, MBBS, BSC

There’s a lot that doctors can tell from a blood test, but some factors affect the accuracy of your results.

In this article, we’ll go through 7 things that can impact your blood test results.

If you’re about to take a test, this will help you plan ahead and avoid anything that can interfere with your results.

1. Not cleaning your finger properly

Unclean hands can affect the accuracy of your finger-prick blood test results.

Before your test, wash your hands with warm water and soap, making sure your hands are completely dry.

Any leftover contaminants like water droplets, soap or moisturisers can affect your readings. 

2. Time of day

Some blood tests, such as our testosterone test, are affected by the time of day you take your sample.

For example, testosterone levels peak in the morning, so you need to take your sample between 7 a.m. and 10 a.m. or your results will seem too low.

In general, blood tests are best done first thing in the morning, just after you wake up.

3. Medications, vitamins or supplements

If you’re taking any regular medication or supplements, these can affect your results.

For example, some labs use a chemical that interacts with biotin (vitamin B7) when they analyse your blood sample. This interaction can skew your results.

Luckily, our partner lab doesn't use this solution – so you don't have to stop taking biotin supplements before using H&B&Me blood tests.

Chat to your GP before you do your test if you have any concerns – and don’t stop taking any prescription medicine without speaking to your doctor.

4. Exercise

A strenuous fitness session may increase a type of protein called creatine kinase in your blood.

Raised creatine kinase levels are a normal part of the muscle-building process, and are to be expected after a workout.

However, doctors often look for elevated creatine kinase levels as a sign of underlying issues. So to avoid concern, don’t do your test straight after the gym!

5. Squeezing your finger too hard

Squeezing your finger with too much pressure can cause your sample to haemolyse.

This means your red blood cells rupture, so your sample can’t be tested properly.

Instead, massage your finger gently in a milking motion to allow the droplets to fall gently into the tube.

6. Clotting

If collecting your sample takes a while, your blood can clot. To stop this from happening, ensure you’re ready with everything set up before you start.

Have a spare lancet ready, and make sure you’ve read the instructions a few times.

If you’ve exhausted all blood from one finger, get another lancet and try the next finger.

After filling each tube, replace the lid and gently tip each sample back and forth to mix it well and stop it from clotting. 

7. Amount of blood

We ask for one or two tubes of blood for a reason!

Some tests don't require much blood, but a lot can happen to your blood sample on the way to the lab before it gets analysed.

Having more blood to work with improves the chance that your sample will be analysed successfully.

The final word

Remember all this when you’re prepping for your at-home blood test. It’ll give you the best chance of getting accurate results.

And, as a rule of thumb, do your at-home blood test first thing in the morning, with clean hands, and when you’re feeling relaxed – so, not straight after your weekly HIIT session!

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