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Why are my Thriva results different to my local GP's?
Why are my Thriva results different to my local GP's?

Have results from your NHS GP come back different to your Thriva results? There are several things that can explain this.

Bianca Crown avatar
Written by Bianca Crown
Updated over a week ago

There's variation in my results

Variation in results is common and can happen for a number of reasons. Here's why there could be differences – as well as specific information for vitamin B12, liver blood test, and cholesterol (lipid profile).

Fasting and medications

Some results can change if you've eaten or taken medications. For example, a high-fat meal close to when you took your sample could raise your triglycerides for a short time. Or if you take medication for a thyroid condition, it can cause your levels to change.

To be able to best compare results, it's important compare tests done in a fasting state. This means you haven't eaten for 8 hours beforehand.


If you collected your sample on different days and at different times, your results can be different. For example, your TSH and testosterone levels can change throughout the day. We recommend doing your test in the morning.

Also, your blood levels can change as you age. So if you're comparing results that were done far apart, there could be differences. 


Lifestyle changes you make even within a few days or hours can affect your results. For example, if you started exercising or taking a supplement in between doing both tests, there could be differences. 

Lab and testing devices

Not all laboratories in the UK use the same procedures or equipment in testing. Our labs maintain the highest standards, and they're used by the NHS themselves.

Our labs use a state of the art Roche Cobas 8000 testing platform. Unfortunately, the nature of the technology means not all platforms will agree with each other. But if two tests are analysed using the same platform, it should be consistent to a degree. 

Also, we only use UKAS compliant labs — UKAS is the international accrediting body for medical laboratory tests.

Units of measurement 

While we use standard UK units, sometimes the units of measurements we use are different to the NHS (for example pmol/L vs ng/ml). This means your results could look very different but are similar once converted.  

Unfortunately we don't offer a unit conversion service.

If you do want to convert these yourself we recommend this online calculator as a trusty source. Just remember to select the for the right test.

Validity of finger-prick vs venous

Multiple studies have validated finger-prick testing in comparison to venous testing.

Specific tests

  • Vitamin B12 

Your vitamin B12 might be different to your NHS result as our labs use the latest Roche analyser (Cobas 8000), while the NHS typically uses an older model. 

If a different analyser is used, then the result is likely to be somewhat different. For the purpose of tracking your vitamin B12 levels, it's important to use the same source for your tests each time. 

The time of day and whether you've fasted or not will also make a significant difference to your result. If you're retesting, try to recreate similar conditions for collecting your sample each time. 

Finally, total B12 levels are very sensitive to supplementing and diet changes. If you retest, keep lifestyle adjustments in mind.

  • Liver blood test

Liver blood tests are known to fluctuate over time and can vary for a number of reasons.

For example, ALT can increase with exercise. And gamma GT can be raised even if alcohol is ingested up to four days prior. It can also fall if taken after a meal. 

We recommend always testing first thing in the morning before eating to avoid these variations.

  • Cholesterol (lipid profile)

Cholesterol tests will vary depending on whether you fasted or not before collecting your sample.  They can also vary within a couple of weeks depending on things like stress, physical activity, and diet. Check out this study if you would like to read some more detailed research about why cholesterol results can vary within a short period of time.

Further questions?

You can provide us with a copy of the results you are comparing your Thriva results to. And we can see what further explanation might be possible.

Email us at 

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