Why does the doctor want me to get bloods taken before 9am?

[bananabanona]

I had a private consultation late on Thursday of last week and the doctor asked me to get bloods and an ultrasound scan done when I'm on my period. I thought my period would probably start at the weekend or early this week so Friday was a mad scramble to try and find someone to do the bloods ultrasound so I don't have to wait another month (my period can be over in a day or two).

Long story short I booked a slot to get my bloods done at my GPs but tomorrow afternoon. I was more focused on the ultrasound as I had to find someone to do that privately so I missed that the doctor asked me to get the bloods done before 9 and have just realised after checking today. I'm supposed to fast overnight.

Is there a reason the bloods have to be done so early or is it just for the patient's convenience to make fasting easier? I can easily fast until the afternoon if it won't mess up the results? Or do I really need to try and rebook?

Also, how long does the overnight fast have to last? And can I have diet drinks? I like the no sugar Tesco lime cordial stuff but is that forbidden?

I thought it was to make fasting easier and would just stick to plain water

Generally it's to make fasting easier and the patient more likely to stick to it and if the doctor wants the sample sent off asap then they try to get you booked in ahead of the first delivery/pick-up for that day.

In my doctors they ask people to come earlier if they are fasting or just to get the bloods off the same day.

In my GPs, all bloods are done in the morning as the samples are picked up by noon and brought for same day testing.

Thyroid testing?

If you are fasting then it is nothing but water.

Thanks Gancanny and toomanyspiderplants - that sounds hopeful if they can still get it sent off in time.

it's to try to rule out a range of things, Polnm .

Only water for how long before Whatthebloodyell? He didn't give a time frame which makes me hope it's not crazily strict. I had a low calorie sweetie within the 12 hour window before I realised I might have to change to 9am if they can do it.

That's usually how it works at my GP's too Elasticate - I was surprised but happy to get something in the afternoon before I realised I'd made the mistake...

I think there are certain bloods that should be done as soon as possible after waking but my memory is failing me re which ones. Cortisol?

It’s my job to analyse blood samples and I would have thought it’s the fasting issue. Also some GP’s only have one pick up and a day old sample is rubbish unless it’s spun down. The fresher the better! Things like Hba1c are fine for up to a week however.

Like whiplashy says, I think some blood tests are more accurate in the mornings. Not quite sure why. Hopefully someone can come along to explain it more.

Could be for a number of reasons but if its blood sugar or cholesterol/lipids that are fasting its probably just to make sure you are fasted but don't suffer too much. Cortisol levels fluctuate during the day so that's often done first thing, to make the results easier to interpret and more reproducable. There was something else I had done once that had to be measured at a particular time but I can't for the life of me remember what sorry! Or it might just be a logistical thing, to catch a transport going to the lab or something. Or possibly a combination of all those things if you are having a lot of tests.
Whatever it is, I hope you get the answers you need and you get well soon.

It's also so that you're not too dehydrated to test, and so that they can get a more "accurate" (average) baseline reading than if you have been starving yourself for longer periods. Your blood sugars would be in your boots if you have been starving for 30 hours, for example.... Hormone levels vary greatly at certain periods of the day, etc. It depends entirely what they're testing for as well.