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Original poster

Can someone talk to me about "fasting" blood tests please?

33 replies

sumsumsum · 24/03/2018 00:13

I'm meant to go in and have a range of blood tests done. I need to be fasting, which the GP said is nothing except water for 12 hours beforehand. Thing is, I'm an insomniac and spend the night quelling anxious thoughts with tea and snacks : is the fasting essential, please? Is 12 hours negotiable? I can obvs avoid snacks but hot drinks are more difficult. Apologies in advance for being a wimp - insomnia is the very devil. If I'd had one cup of tea, and no more than that, would it completely skew the results?

OP posts:
theeyeofthestormchaser · 24/03/2018 00:15

Yes! That’s why they ask you to fast!

Or else they’d say ‘eat whatever you want’ ... Hmm

Original poster
sumsumsum · 24/03/2018 00:16

Haha, I knew I'd be mocked...

Why? Why does it skew them?

OP posts:
adayatthebeach · 24/03/2018 00:17

ONLY water.

JollyGiraffe · 24/03/2018 00:18

Depends what the blood tests are.

Because it affects your blood sugar levels and/or hormone levels. But you haven't said what blood tests they are so can't say exactly.

Original poster
sumsumsum · 24/03/2018 00:23

It's a vast range. I think they want to put me on statins.

OP posts:
nerofire63 · 24/03/2018 00:49

Yeah you need to only stick to water. I can easily do this 12 hours without realizing it but the second someone tells me I have to, I want to eat everything in sight!

TwitterQueen1 · 24/03/2018 11:00

There is absolutely no point at all in having the test if you don't stick to the rule - which is there for a reason. Anything else that you eat or drink will skew your bloods so they will not be able to diagnose you.

Read books, listen to music, download an anxiety app and listen to that.

Hypermice · 24/03/2018 11:02

Only water. Even a sip of tea will throw it. Fasting means fasting.

We regularly have to make people re do it - they insist they’ve been fasting, and on closer questioning they ‘only’ had...

travailtotravel · 24/03/2018 11:03

I have hot water...

Hypermice · 24/03/2018 11:18

Hot water is fine, as long as you were told you could drink water, the temperature is irreverent

But no cheeky squeezes of lemon or anything in it. Honestly, anything else will skew the tests

JollyGiraffe · 24/03/2018 13:17

It seems common sense is really not that common.......

TenancyTroublesAgain · 24/03/2018 13:55

You're having a range of tests done. Anything other than water will skew them.

" Nutrients in the foods you eat and beverages you drink can influence test results. For some tests, even the stimulation of digestion enzymes interferes with test results. The amount of time you need to fast can vary between eight and 12 hours. Glucose and cholesterol tests are examples of blood tests that require fasting."

Chienrouge · 24/03/2018 13:58

Do you think they just tell you these things for fun? Why would they say ‘fast for 12 hours beforehand or it’ll skew the results’ if actually you didn’t have to fast for 12 hours beforehand and it wouldn’t skew the results? For shits and giggles?

SandyShoresMissingShoes · 24/03/2018 16:19

You are making a bit of a song and dance over this OP!

If you eat your last meal at 8pm and your drs appt is between 8-10 am next day you aren't going to starve to death.

To be honest, eating snacks all night long, or at all, is not doing your health any good.And tea surely keep syou awake longer as it's got caffeine in. If you are eating foods with fat and sugar in them overnight, it's not that surprising you may have high cholesterol. (Though it can be hereditary and not linked to diet or lifestyle.)

Elusiveone · 24/03/2018 20:05

I had a fasting blood test thursday and went from 7pm wednesday till 12.30pm thursday and only had water. You will be fine i got over the hunger side of it. Its important to stick to the rules as you would only have to redo it again if you didnt

Original poster
sumsumsum · 24/03/2018 23:33

I did previously have blood tests for cholesterol and blood sugar done by a private GP without fasting.

So why was that?

Thanks for all your lovely empathy, those of you who work in the NHS. I don't just blindly obey - do you? Never ask questions when given an instruction? No?

I don't mind doing what I'm told if it's necessary. Dunno why a private GP would have a different opinion.

OP posts:
Pippioddstocking · 24/03/2018 23:36

The private GP did your tests incorrectly .

Sugarhunnyicedtea · 24/03/2018 23:38

Some blood tests require you to fast. In this instance you are being tested for something that requires a fasting blood test. Unless the tests you had with the private gp were identical you can't compare them. If you can't or don't want to fast you need to speak to the doctor who requested the test

negomi90 · 24/03/2018 23:42

Random blood sugar is not the same as a fasting blood sugar. A random blood sugar which is really really high can be helpful. A random blood sugar which is really really (hypoglycaemic low) can be helpful.
A middling random sugar is useless.

Likewise in terms of cholesterol - some bits can be done without fasting - HDL & total cholesterol. Other bits need fasting (LDL & tryglyceride).

The private tests you had would have provided some information, but not as accurate or as good as if you had fasted.

If they are thinking about statins, they are thinking about your cardiovascular risk profile. Knowing an accurate fasting blood sugar and the different forms of cholesterol are vital for this. So that you can be offered appropriate treatment.
Your health vs a hard night, the choice is yours.
But please be honest, if you don't fast then tell them when you have the test. Lying about fasting will result in your results being misinterpreted which will be dangerous.

Original poster
sumsumsum · 24/03/2018 23:45

At last! An explanation! Thank, Giraffe. It's not actually common sense for the lay person, tis a tad more complicated than that, being science and all, and doctors having different views.

OP posts:
ShakeVigorously · 24/03/2018 23:48

I did previously have blood tests for cholesterol and blood sugar done by a private GP without fasting.

So why was that?

Thanks for all your lovely empathy, those of you who work in the NHS. I don't just blindly obey - do you? Never ask questions when given an instruction? No?

I don't mind doing what I'm told if it's necessary. Dunno why a private GP would have a different opinion.

In that case you probably should have asked the actual GP who ordered the tests Hmm

TooManyWIPs · 24/03/2018 23:49

They can now (within past 5 years or so I think) do an initial diabetes test without fasting as I think they check for a hormone marker rather than actual blood sugar reading, as I have this every 2 years due to being high risk for the condition due to already having other endochrine disorder. I used to have to do the fasting one.
Obviously if the non-fasting test brought up a result that was concerning I assume my gp would then send me for the fasting blood glucose test.
As others have said for the fasting one: only water allowed and if you have the appointment at 9/10am it's easily doable with last cuppa/snack at 7pm
Good luck!

Original poster
sumsumsum · 24/03/2018 23:49

They're thinking about statins because of their QOFs. I can't imagine anyone would lie about not fasting, fgs.

OP posts:
SandyShoresMissingShoes · 25/03/2018 08:04

There was some new research not that long ago which said that for cholesterol tests, fasting didn't make much difference but the NHS is notoriously slow to make changes when new research comes out.

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